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STABILITY OF TERRESTRIAL ECOSYSTEMS AS TO PEST ORGANISMS: AN AXIOMATIC APPROACH

G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH. PART II

G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.

PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I

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AXIOM 8(1) FACTORS of DISTURBANCE of ECOSYSTEM STABILITYto PLANT PESTS and their EFFECTS

To keep ESPPs in any ecosystem on the admissible level as long as possible, it should know the factors, which disturb it. A meaning of the term "disturbance" needs in some sidelight. It should pay attention on the difference between life strategy of biocenoses and destination of articenoses.

The life strategy of biocenoses is directed on keeping ESPPs biomass of the category D‑I on the level 3.1. "Proper control." The decrease ESPPs in this category of biomass under diverse stressors to the level 3.2. "Lag control" endangers biocenoses by a change of composition of dominants. The decrease ESPPs of it on the level 3.3."Late control" results in destruction of biocenoses.

Contrary, on the biomass of the category D‑II, a decrease ESPPs on the levels 3.2. and 3.3. has no a destructive character. In some environmental conditions, it takes place an often decrease ESPPs to the level 3.3. "Late control." The advanced Tolerance of dominants allows biocenoses to survive in spite of the common affection by herbivores. It is necessary, however, a periodic suppression of herbivores by CESPPs 2.5. "Effects of crowding", which provides a reprieve for restoring of vitality of dominants. Therefore, on biomass of the category D‑I, a disturbance changes a character of an ecosystem, and it is undesirable, whereas on biomass of the category D‑II due to advanced Tolerance the term a "disturbance" has no obligatory a negative sense.

The destination of articenoses, which is determined by people, is directed on keeping the level ESPPs 3.1. "Proper control" both in biomass of the categories D‑I and D‑II. When signs of a decrease of ESPPs from the level ESPPs 3.1. "Proper control" appear, CESPPs 2.6. "Human control measures" usually need to be entered in an operation. This is necessary in agricultural crops, where decrease of yielding and keeping of quality of production are the main concern of ecosystems. In ecosystems of other concern, the need of application CESPPs 2.6. "Human control measures" depends on local circumstances.

All the stressors, which decrease ESPPs from the level 3.1. "Proper control", will be referred to as factors disturbing ecosystem stability to plant pests (FDESPPs). Further, it will be considered the conditions, at which diverse FDESPPs are active, and their effects on dominants will be shown.

It has been declared the skepticism as to the durability (persistence) of plant resistance to PPs, which is implied as Antibiosis, due to arising of new pathotypes of phytopathogens and new biotypes of herbivores, which would capable to overcome the resistance.

Indeed, frequency of hereditary changes in PPs is much greater than that in their host-plants. The microevolutionary process that leads to a lost of the resistance in the system of interrelations " a host-plant - a consumer" has been considered by D. Pimental (1961 and other publications), and has got the special term the "genetic feed-back mechanism." Beside the mathematical proof, D. Pimental has given a number of examples, which illustrate the action of this mechanism in nature. It is known a row of cases, at which plant cultivars loss their resistance to PPs in innumerous years after wide-scale growing of these cultivars as field crops.

However, a lot of facts demonstrate the presence of an opposite trend. In this connection, it should mention the words by R.L. Gallun and G.S. Khush (1980, pp. 82‑83), namely: "The breakdown of resistance may occur after few years although in some cultivars resistance remains for the last 50 years."

Consider prospects of keeping of plant resistance to PPs taking into account of FDESPPs and the circumstances, at which they are active, as well as the ways to counteract losses of the resistance.

8.1. Anthropic-1

8.1.1. Growing of cultivars in the range of exotic herbivores r-strategists

Breakage of the prerequisites:

2.1.1.P.1. A hereditary ability of a plant taxon (species, subspecies, phenological forms, varieties strains, hybrids, lines) to resist against a given taxon of PPs

2.2.1.P.2. Adaptation of parasites and pathogens to overcome resistance of their hosts

2.2.1.P.9. Presence of effective vectors of pathogens

8.1.1.1. CESPPs A.2.1.1.2.1. , 2.2.1., and 2.2.3. failed

8.1.1.1.1. Repeated arising of aggressive biotypes inducing outbreaks of the herbivores

As examples of this category, it can be used the cases offered by M.D. Pathak (1970). This is a list of pest insects, including the Hessian fly, Mayetiola destructor and five species of aphids, which overcome Antibiosis of their host-plants repeatedly by producing aggressive biotypes. They are the raspberry aphid, Amphoraphora rubi, the spotted alfalfa aphid, Theriophis maculata, the greenbug, Schizaphis graminum, the corn leaf aphid, Rhopalosiphum maidis, and the pea aphid, Acyrthosiphon pisum.

All the above species are r-strategists. The fly produces up to five generations per season, whereas the aphids have to ten ones or even more. The more number of generations of a herbivore per year, the more hereditary changes in its population, the more probability of arising of mutants with genes, which are able to overcome host-plant Antibiosis, rather that Antibiosis in host-plants to the above herbivores is not well-developed, if any.

These species feed on plant’s parts, which related to biomass of the category D- II. In native lands of the herbivores, these parts are protected by CESPPs A.2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues" in cooperation with CESPPs 2.2.1. "Natural enemies of invertebrate herbivores", A.2.1.2.1.1. "Superevasion from herbivores." or 2.1.1.4.1. "Evasion from herbivores." Being exotic species in North America, they hardly to suffer seriously on the part of natural enemies. At such circumstances, Tolerance is insufficient for self-protection of host-plants. If breeding of varieties having Antibiosis to the herbivores was conducted, the Antibiosis, however, occurred to be not potent, when to take into account specificity of tissues under the affection - young tillers, juvenile parts of stems, and foliage. There are the grounds, therefore, to consider the hereditary prerequisites of CESPPs Antibiosis in the given case as failed ones. In literature, such Antibiosis is characterized as monogenic one or the vertical resistance.

A combination of the above factors: advanced capacity of the herbivores - r-strategists to produce aggressive biotypes, low activity, if any, of resident natural enemies of these exotic herbivores, and weak expression of CESPPs A.2.1.1.2.1. "Antibiosis to herbivores" in the crops results in the loss of Antibiosis. Hereditary prerequisites of this Antibiosis in the above conditions failed.

In this context, it should paid attention that in exotic herbivores K-strategists, an arising of aggressive biotypes has not been traced. This fact was reported again by M.D. Pathnak (1970), in particular, in the wheat stem sawfly, Cephus cinctus and the European corn borer, Ostrinia nubilalis. Further, the plant’s parts, which are affected by these species, might by provided more developed Antibiosis than that in the above herbivore r-strategists. So that, hereditary prerequisites of CESPPs A.2.1.1.2.1. "Antibiosis to herbivores" in the K-strategists are rather durable ones.

Consider the ways to withstand an activity of FDESPPs 8.1.1. "Growing of cultivars in the range of exotic herbivores r-strategists." These ways are practicing of CESPPs A.2.1.2.1.1. "Superevasion from herbivores", A.2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues", and 2.2.1. "Natural enemies of invertebrate herbivores" by means of introducing of them.

The Hessian fly is known in North America from XVIII century, and it continues to be a serious pest mainly of the spring wheat until now. It has been bred a number of cultivars with Antibiosis to this pest, but duration of efficacy of this trait is limited due to arising of aggressive biotypes of the pest. The author has not found in literature reports about introducing of natural enemies of the Hessian fly. Probably, such attempts were been conducted, but they were not insistent.

The aggressiveness of the Hessian fly in America is more expressed than that in Europe. That fact might be explained by difference in activity of natural enemies of the Hessian fly in the compared continents.

Considering of the well-documented situation with the Hessian fly in Russia is able to bring clearness in the issue. This pest probably invaded in this country in the middle of XIX century or its aggressiveness was a result of mutation of a native species, as A.F. Kryshtal (1950) supposed. Over nearly a century, it was very dangerous, when its outbreaks arose with short intervals.

The first outbreak was recorded in Russia in 1847. Since the outbreaks were reported to be in 1879‑1885, 1890, 1896‑1898, 1906‑1908, 1911‑1913, 1923‑1925, 1937‑1938, 1948‑1955, 1961‑1963 (Pavlov, 1967, pp. 47‑48). The level of affection becomes clear from the report by A.Ph. Kryshtal (1947, p. 12). According to this scholar, in 1938, the fly's outbreak was the most sever over 40‑50 preceding years. On 1,621,731 hectares of the surveyed area in Ukraine, density of the fly (the number of larvae or pupae per square meter of the soil surface) reached in the spring wheat 300 individuals on 34.8% of the area and 1000 individuals on 8.6% of the area. In the winter wheat, the affection with the rate over 300 individuals was on 12.8% of the crop's area

Eventually, in USSR, the damage due to the Hessian fly has become less. After 1960-ies, outbreaks of the Hessian fly were recorded and forecasted in 1979‑1980, 1991‑1992 and in 2000‑2001 (Biletsky, 1994). However, any general increase of density of this species in 1987‑2001 in Ukraine was not recorded (G.A. Posylayeva, pers. comm. and author's observations). Over last decades, in the Forest-Steppe biome in Ukraine, it is known only one case of significant damage due to this species, namely: in 1972 several hectares of the winter wheat were damaged seriously by the fly in a breeding center (L.A. Burdenyuk, pers. comm.).

Even in the Steppe zone, where activity of the fly is usually more expressed, it has not been recorded over 1990-ies the decrease of grain yield in the winter wheat at the highest of the revealed values of the density - affection of 46% of tillers in fall and presence of cocoons in 14% in sheaths of stems in summer (Krut, 1992; 1998, pp. 51‑52).

In the past, aggressiveness of the Hessian fly in the Steppe zone was higher. This problem was studied by P.I. Susidko (1969), who reported the following terms of Hessian fly outbreaks in the south of Ukraine (Ibid., pp. 19, 27): 1881, 1884‑1885, 1890, 1892, 1896‑1897, 1907‑1908, 1910‑1911, 1922‑1924, 1930‑1932, 1937‑1938, 1947‑1948, 1951‑1952, 1959, 1966. In 1959, on irrigated wheat fields, the density of the Hessian fly exceeded 1000 larvae per square meter of the soil surface, so that one affected stem contained in average more than three larvae (Ibid.).

This species has developed SP – up to five generations per year that allows it to give a quick rise of density.

P.I. Susidko (1969, p. 19) stressed that outbreaks of the Hessian fly did not demonstrate any periodicity. Its High density continued one-two years. Since then, it took place a depression, which continued from one to ten years.

This view contradicts one keeping by Eu.S. Biletsky (1994), who attempts to connect arising of Hessian fly outbreaks with the periodicity of the solar activity.

As a cause of fluctuation of fly’s density, it might be diversity of weather situations. The role of weather has been stressed by A.F. Kryshtal (1972, pp. 504‑506). He has noted that sharp change weather situation in spring from cold to continual warm one promotes to growth of the density. Contrary, a return of cold weather in spring after short warm weather induces mortality of the neonate larvae. The stable wet weather during summer does not promote an increase of the density, because the flies are active, but they unable find host-plants in the vulnerable stage – with young tillers, which are absent. On the other hand, at droughty summer, the flies stay in diapause. In fall, they become active and find abundant young tillers on winter wheat fields. In addition, wet weather over summer promotes activity of chalcidid parasites of the Hessian fly, whereas droughty summer suppresses them (Rubtsov, 1938).

As an explanation of the trend to decrease of aggressiveness of the Hessian fly, it can be proposed an adaptation of resident natural enemies to use this species as a host. For substantiation of this proposition, it can serve the data offered by A.V. Znamensky (1926, p. 213). These data allow comparing mortality of a fall generation of the Hessian fly in Poltava (Ukraine) in 1923 at the early sowing date, and in Lafayette, Ind. (USA). The observations in Lafayette were conducted between September 11 and October 16, 1921. As to Poltava, the data are obviously original ones by A.V. Znamensky. A source of the data for Lafayette was not noted. In the Table 38, it is shown the comparative mortality of a fall generation of the Hessian fly in the stages of egg, larva, and pupa.

Table 38. The comparative mortality of the Hessian fly in Poltava (Ukraine) in 1923, and in Lafayette, Ind. (USA) in 1921

Location

Crop

The number of studied objects

Percentage of plantlets with eggs

Percentage of objects with larvae and pupae

The number of eggs per plantlet

The overall number of eggs

The overall number of larvae and pupae

Survivorship, percentage

Plantlets

Tillers

The number of tillers per plantlet

Plantlets

Tillers

1

2

3

4

5

6

7

8

9

10

11

12

Poltava

The winter wheat

212

1695

8

100

44

52

56

11872

28

0.23

The winter rye

189

1701

9

87

7

6

19

3116

7

0.22

Lafayette

The winter wheat

50

135

2.7

100

69

44

36

1796

284

15.8

The winter rye

50

410

8

90

6

0.7

12

580

7

1.3

The Table 38 demonstrates the great difference in survivorship of the Hessian fly between the areas. In Lafayette, Ind. (USA), the survivorship was much higher than that in Poltava (Ukraine). The difference can be due to the better adaptation of natural enemies (probably parasites and pathogens) to this insect host in Poltava comparing with that in Lafayette.

Why does the activity of natural enemies of the Hessian fly in Poltava is greater than that in Lafayette? The answer is the rich fauna of relatives of the Hessian fly in Ukraine. In Europe, including Ukraine, it was recorded a number of species of the genus Mayetiola: M. avenae March., M. dactylidis Kieff., M. destructor Say, M. joannisi Kieff., M. schoberi Barnes, and M. poae Bosc. (Mamayeva and Mamayev, 1981).

In Ukraine, on the Hessian fly, it has been recorded twenty species of parasites (Bilanovs’ky, 1940, cited in A.F. Kryshtal, 1974, p. 505). From them, the most numerous are Eupteromalus micropterus, Merisus destructor, Platigaster minutula, and Eupelmella vesicularis.

As an example of potency of the parasites, it can serve the wasp Platygaster minutula Lind., Proctotrupidae, which oviposites in eggs of the Hessian fly, and the progeny finishes development in larvae or pupae; due to polyembriony, 15‑20 larvae of the parasite develop from one of its egg (Shchegolev et al., 1949, p. 389).

An activity of the parasites is high in vicinity of forest plots and shelterbelts (Kryshtal, 1974, p. 505).

In wild vegetation, important role in SES is played by CESPPs 2.1.1.4.1. "Evasion from herbivores" operating on the level of separate plants. In crops, it is very effective of CESPPs A.2.1.2.1.1. "Superevasion from herbivores." Sowing of winter wheat in the optimal dates, which have been determined for diversity of States, prevents exposition of plants in vulnerable stage on the flies (Fernald, 1926, p. 316).

The Superevasion is prospective concerning the spring wheat. In fact, "In the spring-wheat section late seeding will not apply. It seems likely, on the contrary, that the earlier it is sown in spring the less it will suffer from the Hessian fly" (Fernald, 1926, p. 317).

The trait A.2.1.1.3.1.2. ''Tolerance to herbivores, Repair or compensation of losses of host-plant tissues'' allows the crops to survive in spite of significant activity of the Hessian fly.

Turning to the Table 38, it is noticable high general tillering of the crops – eight tillers in the winter wheat and nine tillers in the winter rye. Abundant tillering allows to plants to tolerate losses of their tillers due to affection by the fly in fall, and to restore tillers in spring. To overwinter succesfully, a plant needs in only two tillers.

Nevertheless, CESPPs A.2.1.2.1.1. "Superevasion from herbivores" is insufficient for reliable protection of the spring wheat and in the winter wheat on condition that it grows in southern areas, where the fly can be active over winter. In such a situation, it is need cultivation of the varieties possessing the trait of expressed Antibiosis to the Hessian fly.

The Antibiosis is prospective, particularly in North Kazakhstan. Here, Mayetiola destructor is a tiresome pest (Yevdokimov et al., 1986). In these climatic conditions, it is possible to grow only the spring wheat, so that Superevasion is insufficient for the protection. Arid climate does not promote abundant general tillering, so that Tolerance is also insufficient. Further, areas of natural woody ecosystems and shelterbelts, where pest's parasites and predators find favorable conditions for overwintering and additional (imaginal) feeding, are actually absent. At last, here it is practiced the soil treatments without digging up. In this area, it is necessary the surface tillage - sharing for protection of the soil from wind erosion. That is why the fly overwinters successfully into shready stalks, whereas the wheat is grown as a monoculture.

At growing of wheat cultivars with Antibiosis to the Hessian fly, recurrence of outbreaks takes place at arising of aggressive biotypes of the pest. Contrary, growing of the winter wheat in the conditions, where Superevasion is effective, Tolerance is developed, and natural enemies of the fly are prosperous, results in unlimited keeping of its density on the Insignificant level.

Population dynamics of the exotic species of aphids is similar to that of the Hessian fly. This suggesion is concerned to the above-cited species Amphoraphora rubi on the raspberry, Theriophis maculata on the alfalfa, Schizaphis graminum on the wheat and the sorgum, Rhopalosiphum maidis on the sorgum and the corn, and Acyrthosiphon pisum on the pea, rather that Antibiosis against them is not expressed well. In their EEs in the native land, the role of Tolerance and activity of natural enemies is supposedly great one, so that there is no need in developed Antibiosis. A cooperation of all the above CESPPs provides admissible suppression of their density. Contrary, in the recently invaded area, low activity of natural enemies results in rather soon loss of Antibiosis. On the other hand, Tolerance is insufficient for self-protection in the conditions of high activity of herbivores – r-strategists.

Causes of outbreaks of the Russian wheat aphid, Diuraphis noxia Mordv. (in the contemporary Russian literature, this species is known as Brachycolus noxius Mordv.) can be included in this category of FDESPPs. In Russia, this species was described at the end of XIX century, when it occurred to be very abundant. In fact, N.A. Kholodkovsky (1912, p. 488) reported that this species (at that time, it was used the name the barley aphid, Brachycolus korotnevi Mordv.) was appeared sometimes in huge masses in south of Russia, and its imagoes composed vast clouds. Probably, this species penetrated into this country shortly before the outbreak. Eventually, density of this species has become Low although breeding of resistance cultivars has not been conducted.

Contemporary literature does not report about outbreaks of this species in the areas of its former abundance in East Europe. Diuraphis noxia is mentioned as a satellite of more important pest - Sitobion avenae in south Ukraine (Nikolenko and Omel'chenko, 1974). In the Forest-Steppe zone, the role of the aphid is considered as insignificant. In fact, the studies in 1976-1979 showed the presence of four species of aphids on the winter wheat, including Diuraphis noxia, however, the occurrence of Sitobion avenae equaled 92.4% (Dudnik, 1983, p. 6).

In East Germany, participation of Sitobion avenae in a total aphid stock on the winter wheat was about 90% (Assman and Wetzel, 1990) that also suggested the minor role of Diuraphis noxia.

It was reported that Diuraphis noxia is a species of the Central Asia origin (Schliephake et al., 1998). It spreads westward beginning with XIX century. The Low density of this species in Europe in nowadays might be explained by adaptation of resident natural enemies to suppress it.

FDESPPs 8.1.1. cooperates with FDESPPs 8.6.1. "Invasion of exotic taxa of phytopathogens or herbivores, which are able to overcome 2.1.1.2."

8.1. Anthropic-1

8.1.2. Growing of a single cultivar on vast areas



8.1.2.1. CESPPs A.2.1.1.2.2. failed

8.1.2.1.1. Arising of high virulent pathotypes in resident phytopathogens r-strategists inducing epiphytoties

The more an area of growing of a cultivar, the greater a probability of a contact of its plants with virulent pathotypes existing in nature, the more abundant agents of phytopathogens contact with these plants, the greater a danger of arising of new virulent pathotypes. That is why a trait of Antibiosis to phytopathogens can be lost over innumerous years after beginning of growing of a resistant cultivar on vast areas. This factor is of big importance in the present time. Modern agriculture practiced in developed countries is characterized by the growing of a few cultivars of a crop on vast area. This is a general trend of the progress, when the best cultivars quickly get recognition of numerous growers.

Resistant cultivars growing on minute areas, for examples in nurseries of breeding centers stay out of above threats. Here, a trait of the resistance remains much longer than that in the situation described above.

This FDESPPs is potent in phytopathogens r‑strategists such as the rust and mildew species having numerous generations per year and high mobility of their spores. As consequencies of r‑strategy, it is great hereditary variability. Within a species of the phytopathogens, there exist hundreds of pathotypes. In them, it lacks the stage of saprophy, which are characteristic for K‑strategists, in particular for the root rots. A lack of saprophagy promotes a hereditary variability in a phytopathogen’s population.

The selection with the trend of an increase of virulence leads to extinction both of the pathotype and their host‑plants as well as to defeat of a high‑virulent pathotype in competition with pathotypes of less virulence. At this trend, the durability of host-plant Antibiosis is low, but this is a blind alley in microevolution of phytopathogens. This trend, which appears at growing of a single cultivar on vast areas, directs of a phytopathogen on the way of of high, but short-time virulence.

When growing a cultivar over vast areas, a loss of CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" is influenced by diversity in virulence of subspecies taxa of a phytopathogen depended on a locality. M.P. Lesovoy (1977, and subsequent publications) stated that composition of races (and pathotypes) within a species is diverse even on rather small distance. Thus, in Ukraine, there are twenty Regions. M.P. Lesovoy and co-workers reported that among these Regions, there are significant differences, in particular as to virulence of pathotypes. The occurrence of them (eigtheen pathotypes of the race 77 of the leaf rust) on seven wild gremineous species in some localities is so significant that growing in them of certain varieties of the winter wheat is took the risk (Lesovoy, 1977, p. 24). Notably, that presence of high virulent pathotypes does no preclude thriving of wild plant species.

The diversity yielding of crops depending on a locality is known long ago. In Soviet Union, it was organized a service of the Seed Testing Stations – test plots, where newly bred varieties were proved on diverse agronomic traits. In Ukraine, in every Region, it has operated such a Station. The differences in yielding indeed were recorded in spite of varieties were grown in favorable for a given crop habitats, and differences in climatic conditions sometimes were little. After advantages of a variety are proved, a recommendation to grow a variety in a given Region is given.

It is accepted that at growing of a variety with monogenic (vertical) resistance on vast areas, it will be overcome by r-strategists during few years at least in some localities.

When FDESPPs 8.1.2. "Growing of a single cultivar on vast areas" operates in a cooperation with FDESPPs 8.1.3. "Growing of cultivars in the conditions of a lack of operation of CESPPs A.2.1.2.4.1." loss of CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" gets more probable.

In phytopathogens K-strategists, the situation is different one. The fact is the potato varieties resistant over many years to the wart (cancer) disease, Synchytrium endobioticum Schild., whereas in the case of the potato leaf blight, Phytophthora infestans (Ment.) De Bary the trait of resistance is of short duration. Yu.T. D’yakov (pers. comm.) explains these facts by different strategies of these phytopathogens: the category "K" in the case of the cancer, and "r" in the case of the blight.

8.1. Anthropic-1

8.1.3. Growing of cultivars in the conditions of a lack of operation of CESPPs A.2.1.2.4.1.



A.2.1.2.P.2. In articenoses, a resemblance of a dominant stock to that in biocenoses or special cultural practices with the aim of effective operation of CESPPs 2.1.2.

8.1.3.1. CESPPs A.2.1.1.2.2. failed

8.1.3.1.1. Arising of high virulent pathotypes in resident phytopathogens r-strategists inducing epiphytoties

Host-plants select their phytopathogens on virulence. Only those pathotypes of them survive, which are able either to co-exist with host-plant Antibiosis or to overcome it. As to the latter, i.e. a loss of Antibiosis, the successful pathotypes produce agents, whose chance on survivorship is different depending on a character of a stock of host-plants within an ecosystem. If the stock consists of a single cultivar, its protective trait (Antibiosis) is the same in all the plants. Therefore, there are no obstacles for a successful pathotype to infest all the stock. Because the number of generations per year in r‑strategists is numerous, an infection spreads quickly over a stock. This capacity is called a high aggressiveness of a pathotype.

Further, in this situation, it increases virulence of a phytopathogen species due to an increase of participation of the most virulent pathotype. This is so because in the conditions of an unlimited spread of infection, it arises an intensive competition among micelia. In the competition, it survives the micelia, which have better possibility to suppress Antibiosis of host-plant, so that they force out less virulent pathotypes. Therefore, at the monotonous hereditary composition of a stock of host‑plants, it gives rise new pathotypes with ever‑increasing virulence. This trend, however, takes place on susceptible cultivars. Contrary, on the cultivars with Tolerance, take place an opposite trend. Then, less-virulent pahotypes force out high-virulent pathotypes.

From ancient times, humans have known consequences of the above process. Therefore, they bred and used so called land races of crops. Now, it is known that a land race is composed by a number of hereditary very different entries, which, however, are identical in their agronomical, phenological, and morphological traits.

This problem was considered above in this text at characteristic of CESPPs of the category A.2.1.2.4.1. "Hereditary heterogeneity of a stock of host-plants." In the same Section, it mentioned the ways to counteract the process of increasing agressiveness and virulence of phytopathogens. The ways consist in development of methods as to increase of hereditary diversity in a stock of crops. In other words, this is the concept of intrafield diversification, which concerns growing of divers cultivars in mixture. In such conditions, both virulence and aggressiveness of phytopathogens are dumped; it survives the pathotypes, which are able to coexist with their host-plants, so that Tolerance thrives.

In the case of operation of CESPPs 2.1.1.3.2. "Tolerance to phytopathogens" and intrafield heterogeneity, the more virulent pathotypes have no advantages comparing with less virulent ones. Therefore, the above mentioned trend of forcing out of high-virulent cultivars by less-vitulent ones becomes especially expressed.

The FDESPPs 8.1.3. operates usually jointly with FDESPPs 8.1.2. "Growing of a single cultivar on vast areas" that redouble the negative effect of such cultural practices.

8.1. Anthropic-1

8.1.4. Growing of cultivars in the conditions unfavorable for expression of

CESPPs A.2.1.1.2.



2.3.P.2. Limitation of aggressiveness of PPs

8.1.4.1. CESPPs A.2.1.1.2.1. and A.2.1.1.2.2. failed

8.1.4.1.1. Affection by phytopatogens and herbivores

It was recorded a phenomenon, which considering by scholars as an evidence of dependence of expression of Antibiosis genes on ambient temperatures. The case stories were considered above at characteristic of CESPPs 2.3. "Routine weather suppression."

In short words, affection of some wheat varieties by the Hessian fly occurred to be equals 3% at 15°C and 97% at 27°C (Painter, 1958). The similar results were obtained in another study (Sosa and Foster, 1976).

In phytopathogens, it was recorded a sudden loss of Antibiosis to the leaf rust on the winter wheat at a sharp skip of the weather situation from cold spring to hot summer (Gorlach, 1958, p. 147). The loss took place two seasons. At other weather situations, these varieties were resistant to the leaf rust over many years.

At last, significant fluctuations of Antibiosis depending on weather situation were recorded in species of the cabbage to Plasmodiophora brassicae Wor. (Tyuterev, 1981).

These cases show that Antibiosis to PPs can be lost in some seasons at specific weather situation or even continually if a variety is grown in the climatic conditions, where destructive weather situation is common.

8.1. Anthropic-1

8.1.5. Growing of cultivars in the conditions intensifying SP of PPs




2.4.P.1. Keeping of severity of the season of an year when activity of PPs is suppressed

8.1.5.1. CESPPs A.2.1.1.2.1., A.2.1.1.2.2., and A.2.1.2.1. failed

8.1.5.1.1. Affection by phytopathogens and herbivores

In tropical and subtropical climates, PPs are able do not stop their development over entire year. Application of irrigation leads to the same situation even if climate of an area includes a dry season. The factor of a seasonal limitation does not operate, when growing of agricultural crops in greenhouses independently to climate of an area, if summer interval in growing does not practiced. In such conditions, it increases both the number of generations of PPs and velocity of completion of life cycle. In so doing, an increase of populations becomes maximal.

Because CESPPs 2.4. "Periodic (bottle-neck) suppression" does not operate, CESPPs A.2.1.2.1. "Superevasion" does not operate also. Further, an amount of agents of phytopathogens becomes so large that they can overcome even advanced Antibiosis.

The same might be true for herbivores, especially sap-sucking ones. This is an increase of their aggressiveness.

A virulence of phytopathogens grows also. This is so because at competition of overcrowded micelia, the most virulent mutants obtain selective advantage. The stages of saprophagy and dormancy, which retard selection on the best parasitism, are absent. This is an additional factor of increase of virulence. Thus, CESPPs A.2.1.1.2. "Antibiosis" is ineffective.

The above conditions are very valuable for estimation of CESPPs A.2.1. "Plant resistance to PPs." If an entry occurs to be resistant in such a severe pressing on the part PPs, its resistance would be durable in less severe conditions.

8.1. Anthropic-1

8.1.6. Growing of cultivars with spontaneous decrease of CESPPs A.2.1.1.2.2. especially at specific weather situations




8.1.6.1. CESPPs A.2.1.1.2.2. failed

8.1.6.1.1. Affection by phytopathogens

This category of losses of CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" has not been described in literature yet. Therefore, it deserves a consideration in detail, rather that the counteraction to this FDESPPs seems to be prospective to bring clearness in the principal issues of plant resistance to PPs.

The widely accepted concept assumes that plant resistance to PPs is durable if it has the polygenic character, whereas a durability of the monogenic resistance occurs is a rare event. However, it is not easily to gain an understanding, which kind of character (monogenic or polygenic) a resistance has in a concrete case.

To illustrate this statement, consider the case of a loss of resistance of the winter wheat varieties Avrora and Kavkaz to the leaf rust, Puccinia recondita Rob. ex Desm. f. sp. tritici Erikss.

In the North Caucasus Area of Russia after 1960, the winter wheat variety Bezostaya-1 got a wide spread ensuring highest grain yield for that time – 4-5 metric tons per hectare in the best environmental conditions. With the aim to shift this variety by more productive ones, in 1968, it was bred the varieties Avrora and Kavkaz, which produced 5-6 metric tons of grain per hectare. High resistance to the leaf rust, which was a serious disease in that region, was a valuable trait of these varieties.

M.P. Lisovyi (2001, p. 17) reported that "Any known in that time race of the leaf rust did not affect them. The author of these varieties Academician P.P. Luk’yanenko supposed that their resistance to the phytopathogen would be not never lost."

The valuable traits of these varieties resulted in the rush increase of areas of cultivation of them. In the North Caucasus and Ukraine, the areas reached such values: in 1971 – 19,000 ha, in 1972 – 337,000 ha, and in 1973 – 1,367,000 ha. In 1973, it came a crash. M.P. Lisovyi (2001, p. 18) wrote: "The fact of a loss of the resistance by the varieties so affected of health state of the breeder Academician P.P. Luk’yanenko that he died due to a heart infarction on a field of the wheat got brown in result of affection with the rust."

What is the cause of such sudden loss of the resistance? M.P. Lisovyi (1977) supposed that the cause consisted in an arising of new high virulent pathotypes of the race 77 of the leaf rust. They were marked 16, 20, 22, 23, 25, 26, and 28. Further, he considered this case as a didactic example of a failure of the monogenic (vertical) resistance (Lisovyi, 2001, p. 18).

But there exists a doubt as to validity of this statement. The resistance was considered as monogenic one, despite these varieties had been bred as resistant to all the races of the leaf rust as it was noted above. Further, it is rather strange that new-arisen high virulent pathotypes of the race 77 so quickly (during one growing season) spread over the vast areas. It needs an additional information to explain the above questions.

First of all, the studies in the North Caucasus in 1973 at the epiphytoty of the leaf rust did not find out any new high virulent pathotypes of the race 77 (Rudnev et al., 1975). The main pathotype that induced this epiphytoty was the well-known 103 of the race 77. Further, this pathotype affected not only the varieties Avrora and Kavkaz, but all the varieties grown in this region, including Bezostaya‑1, as well as the wild gramineous species – Agropyrum dereshrum Fisch., Aegilops sp., Bromus squarrosus L., B. arvensis L. ,and B. scoparius L. As to the wild species, it is difficult to suppose that they also have the monogenic type of the resistance.

The report by E.D. Rudnev et al (1975) suggests an impact of the factor unconnected with the increase of virulence of the phytopathogen, which has induced this general epiphytoty of cereals. As to the case of Avrora and Kavkaz, another line of reports indicates on operation of inapparent processes in heredity of these varieties.

In 1969‑1970, resistance of these varieties to the leaf rust was studied by means of artificial inoculation by diverse pathotypes of the leaf rust (Shopina et al., 1972; Krayeva and Alekseyeva, 1972). These studies showed that most part of plants in Avrora and Kavkaz were resistant to all the rust pathotypes, but a few plants were susceptible to the race 143; some plants were susceptible to the races 77 and 122. In addition, the percentage of susceptible plants depended on a provenance of seeds ("lines" according to these scholars’ words). Those from the L’vov Region (Ukraine) were affected by the leaf rust on the level 60-80% –much more than the plants from seeds grown in other Regions.

The similar results were obtained in studies in Ukraine also before the epiphytoty (Lesovoy and Fyodorova, 1974). In that time, nearly 95% of plants within Avrora and Kavkaz were resistant to all the pathotypes of the leaf rust, whereas the rest were susceptible to a number pathotypes including the wide-spread races 21, 57, 77, 92, 130, 149, as well as the new, but unidentifined races marked X1, X3, X8, X9. The proportion of the unindentified races was only 2-8% in various experiments.

Further, the studies by V.F. Peressypkin et al. (1975) revealed a decrease of resistance of Avrora and Kavkaz over several years in succession, and an influence of ecological conditions on the rate of the resistance loss.

What is the factor, which has caused this epiphytoty? In literature, there is a legible answer to this question. Here are the words by P.S. Udintsov (1974, p. 39): "In last year (in 1973), in the period of vegetation in North Caucasus, in the Regions of the Center (the Forest‑Steppe), the Central Chernozem Area, and the Volga River Basin, in many Regions of Ukraine, it occurred to be very favorable weather conditions for activity of the leaf rust on the wheat. The widest spread of this disease was recorded in the Krasnodar Region. Here, in the preceding fall, it was accumulated a great many infection on voluntary wheat. After a good overwintering and exclusively favorable conditions for the phytopathogen in spring and summer, it arose an epiphytoty of the disease. In some fields, the wheat varieties Avrora and Kavkaz, which formerly were considered as resistant to this phytopathogen, were affected on 80‑95% especially on areas with early sowing dates and a high rate of fertilization by nitrogen comparing with the rate of fertilization by phosphorus and potassium."

E.D. Rudnev et al. (1975) also supposed that the epiphytoty was provoked by weather conditions favorable for activity of the leaf rust, rather than by arising of a high virulent pathotype.

The provocative role of weather situation favorable for the leaf rust was noted in the previous literature. Here is the report by M.V. Gorlenko (1973, p. 217): "According to the data by A.A. Gorlach (1954), a sharp change of outer conditions led to weakening and subsequent loss of wheat resistance to the leaf rust. In 1951 and 1953, in the Belaya Tserkov District (Ukrainian SSR) after prolonged cool in spring, it came suddenly hot weather. This led to serious affection of resistant varieties of the wheat by the leaf rust. Bad overwintering also can increase susceptibility of resistant varieties. Therefore, to be resistant to the leaf rust, varieties need to be provided by traits of winter-hardness and drought-hardness."

In The V.M. Remeslo Myronivka Institute of Wheat, in 1999 it was observed the mass affection by the leaf rust of all the wheat entries with the exception of the variety Kryzhynka. Here, in 2001 at uncommonly wet weather in spring and summer, nearly all the entries were affected by the root rots and the saprophagous fungi on spikes. The only exception was the variety Remeslivna.

Nevertheless, in above cases, a decrease of the resistance took place only over a season with the peculiar weather situation. On the other hand, the epiphytoty of 1973 showed the continual fail of the resistance in the Avrora and Kavkar. In a result, these varieties disappeared from grower’s fields.

An irrigation of wheat fields practiced in areas of arid (warm) climate enhances affection of the wheat with the leaf rust, so that a decrease of grain yield reaches 4‑5% (Chumakov, 1963, cited in J. Lilley, 1976). This finding might be explained by setting up optimal conditions for vital activity of the leaf rust at combination of high humidity of air and favorable ambient temperatures. These data suggest heavy affection by the leaf rust, because irrigation increases grain yield if it does not accompanied by disease. This is another example of greater importance of weather situation than hereditary grounds of resistance to a phytopathogen.

The similarity of such effects might be seen at considering the data of laboratory studies, where the resistance was evaluated at optimum for vital activity of phytopathogen agents. In fact, the varieties of winter wheat Myronivs’ka‑33 and Myronivs’ka‑34 were nearly immune to the leaf rust at evaluating in conventional breeding nurseries. However, when they were evaluated being inoculated by this phytopathogen in the laboratory conditions, a significant part of their plants (32‑67%) was susceptible or had low resistance (Rudenko, 1997).

In the environmental conditions favorable for a given phytopathogen species, it grows infectious loading by its agents and their vitality, i.e. its aggressiveness. This brings danger for any its host-plant. In addition, these conditions are able to decrease protective response of host-plants, because for expression of resistance trait, it needs staying of environmental factors in some range.

In fact, there are the data about the important role of air temperature for expression of resistance in the wheat against the stem rust. N.H. Luig and S. Rajaram (1972) showed that genes of resistance to the stem rust, Puccinia graminis Pers. f. tritici Erikss et Henn. are inactivated at temperatures 27‑30°C. The same might be true for the resistance to the leaf rust in the varieties Avrora and Kavkaz. High percentage of susceptible plants in populations of them from the L’vov Region according to G.A. Krayeva and T.P. Alekseyeva (1972) suggests validity of this idea. The climate of the L’vov Region differs significantly from the above-mentioned territories (the Kiev Region, and especially the Krasnodar Region). This resistance can be fixed in heredity of the varieties being temperature-depended or moisture-depended.

Turning to the question of the character of rust resistance in the varieties Avrora and Kavkaz, it should note that the supposition as to the monogenic type is based on the only experiment. In the experiment, it was obtained F1B1 of the first backcross with Avrora and Kavkaz as donors of the resistance, and the variety Mironovskaya-808 as a recipient. In this generation, the number of plants resistant and susceptible to the race 77 corresponded the ratio 1:1 at rather low index of validity (P) – 0.95+/-0.25 (Lesovoy, 1977, p. 40).

The conclusion from this experiment that the resistance of Avrora and Kavkaz has a monogenic character is dubious, rather that exactly M.P. Lisovyi (2001, p. 17), has spoken the words: "Any known in that time race of the leaf rust did not affect them." This is charateristic just for polygenic resistance.

How do to explain above data from concepts of genetics? It has been known the patterns of gene activity within a taxon, which was defined by N.V. Timofeyeff-Ressovsky as the penentrance and the expressiveness of a gene (cited in M.E. Lobashov, 1967, pp. 567‑568). The penentrance is determined by percentage of organisms with a certain trait, when the organisms stay in the same conditions. This index shows a uniformity of a taxon’s population. The expressiveness is determined by percentage of organisms with a certain trait, when they stay in diverse conditions. Thus, the latter shows the response of a gene on factors of the environment.

The varieties Avrora and Kavkaz had the high penentrance of gene resistance to the leaf rust in the conditions far from optimum for this phytopathogen, but their expressiveness occurred to be low, when the conditions become optimal. In subsequent years, this defect took place at any conditions, i.e. the trait of the high penentrance can be lost entirely.

The capacity of the variety Bezostaya-1 to produce good yielding in the conditions favorable for aggressiveness of the leaf rust implies advanced expressiveness of this variety.

In the field evaluation of resistance of wheat varieties to the leaf rust, the Myronivs’ka‑33 and Myronivs’ka‑34 had high penentrance in the non-optimal conditions to the rust, and the low indices of expessiveness in the optimal for the rust conditions in a laboratory.

Above consideration allows drawing some conclusions as to causes of loss of resistance on the example of well-studies interrelations – the wheat and the leaf rust as follows:

i) The speculations as to resistance to the leaf rust is determined exceptionally by the number of relevant genes are not convincing.

ii) There exist the factors, which induce a progressive decrease of the resistance in successive generations with participation of destructive effect of some weather factors.

iii) The loss of resistance might be induced by an operation of FDESPPs 8.1.6. "Growing of cultivars with spontaneous decrease of CESPPs A.2.1.1.2.2. especially at specific weather situations."

iv) The loss of resistance might be induced by an operation of FDESPPs 8.1.4. "Growing of cultivars in the conditions unfavorable for expression of CESPPs A.2.1.1.2."

v) It might be the effect of FDESPPs 8.1.6. in successive generations proceeds as follows. The plants within a stem stock compete with each other. In so doing, they undergo natural selection on the part of diverse stressors (capacity to utilize resources, to withstand frost, resistance to other phytopathogens, etc.). Plants with the better capacity can have advantages comparing with plants having resistance to the leaf rust. Percentage of the latter decreases, i.e. penentrance of the gene of resistance in successive generations becomes lower.

DISCUSSION

The data on FDESPPs of the category 8.1. "Anthropic (hereditary imperfection of cultivars at certain circumstances") inspire to consider the issue of durability of plant resistance to PPs in the context of microevolutionary processes in the system "a host-plant – a consumer." In so doing, it will be used the data for both in agricultural crops and wild species, as to phytopathogens and herbivores.

The epiphytoty of 1973 allows understanding a sense of plant resistance to phytopathogens in crops. The sense consists in a holding of grain yield, rather than in low values of affection indices. This becomes clear, when comparing the yielding and affection of various wheat varieties.

In 1973 in North Caucasus, the losses of grain yield were the following: Avrora – 20%, Kavkaz – 16%, Bezostaya‑1 – 9% (A.A. Morozova, 1974, cited in N.M. Stepanov et al., 1976). The less loss in Bezostaya-1 is of a special interest. The matter of fact that before the epiphytoty, this variety was known as susceptible to the leaf rust in contrast to the resistant Avrora and Kavkaz. All the plants of Bezostaya‑1 were susceptible to most of pathotypes of the leaf rust (Krayeva and Alekseyeva, 1972).

In the the study by A.M. Dymchenko et al. (1990), it was evaluated of resistance of sixty-seven wheat varieties at heavy doses of inoculum by eight pathotypes of the leaf rust. In it, Bezostaya-1 occurred to be the first as to rate of affection (75‑100% of a leaf surface) and the least as to yield loss – 0.6‑0.8 metric tons per hectare.

The capacity of Bezostaya‑1 to maintain high grain yielding at heavy loading of pathogen’s agents is a good example of supremacy of CESPPs A.2.1.1.3.2."Tolerance to phytopathogens" comparing with CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" as a means of self-protection.

The data of studies cited above show that an inoculation by actually all the pathotypes including those known as high virulent on Bezostaya‑1 occurs to be successful. Hence, this variety is able to enter in compatible interrelations with every of them. According to the classification of the present report, this is CESPPs A.2.1.1.3.2.2.1. "Tolerance to phytopathogens, Symbiosis with former parasites, Compatibility."

The gene sources, which determine such traits of Bezostaya-1 are shown by M.E. Lobashov (1967, pp. 639‑640). In this book, it is presented the pedigree of this variety. Among its ancestors, there are twenty-one varieties including well-known foreign and resident ones close to land races. The former includes Squarehead, Spyk, Lancaster, Fulz, Klein‑33, Kanred, Rieti and others. The resident varieties are presented by Ukrainka, Krymka, Yefimovka, Mestnaya (this Russian word means "local"). One of the nearest ancestors is the variety Skorospelka-2. (this Russian word means an "early matured crop"). This implies that Bezostaya‑1 has one more trait – CESPPs A.2.1.2.1.2. "Superevasion from phytopathogens."

In subsequent years, to replace Bezostaya‑1, it has been growing the more productive varieties with significant A.2.1.1.3.2. "Tolerance to phytopathogens" to the leaf rust. One of them, it was the variety Myronivs’ka‑61, which having a moderate numeric score of the resistance - 5 (the maximal score in the scale is 9), had been a leader in Ukraine as to grain yielding over 10 years until 2000.

In 1990, this variety was aworded with the Golden medal in All-Union Exhibition of Achievements of Soviet Economics in Moscow. Such an awordment occurred to be the last in history. In 1991, Soviet Union underwent a collaps.

Yu.T. D’yakov (1985, p. 168) has reported that the Tolerance is accepted as most prospective factor of resistance of the wheat and the oat against the mildew, Erysiphe graminis D.C., f. tritici March. At breeding on the resistance, it is practiced to cull both heavy affected plants and immune ones, whereas plants with the moderate level of the affection are selected. The mildew has exclusive capacity to produce new pathotypes, so that its capacity to overcome Antibiosis is well developed. The immune plants have less productivity than those with the moderate level of affection, because the former spend more resources for self-protection.

The heredity of wild plant species has not been changed by breeding. Therefore, it should suppose that the hereditary base of their resistance to phytopathogens is quite potent. That is why, it is interesting to consider these interrelations. The study have been conducted by M.P. Lesovoy (1977, p. 24) on seven species of wild cereal species showed that they year after year have signs of affection by eighteen biotypes of the 77 race of the leaf rust. The wild species are considered by this scholar as a source of high virulent infection for cultivated cereals, and as a cause of significant losses of grain yield.

The effect of the leaf rust on productivity or vitality of wild species has not been studied. But simple speculations suggest that the negative effect is negligible, if any. Otherwise, vitality of plants in these species would be suppressed, and they would be replaced by healthy competitors. Thus, the considered interrelations are concerned to the Tolerance. Most probably this is CESPPs 2.1.1.3.2.2.1. "Tolerance to phytopathogens, Symbiosis with former parasites, Compatibility" or CESPPs 2.1.1.2.3.2.2.2. "Tolerance to phytopathogens, Symbiosis with former parasites, Mutualism."

The durability of the CESPPs 2.1.1.3.2. "Tolerance to phytopathogens" has the theoretical grounds. In this case, microevolution of phytopathogens is directed on success in competition with pathotypes, which co-exist with their host-plants, rather than on growth of virulence. This fact has been noted by J.F. Schafer (1971, p. 248) in the following words: "The lack of selective pressure on the pathogen, making tolerance more stable than true resistance (M.D. Simons) is the one big advantage of tolerance over resistance which provides equal protection."

Further, low virulent pathotypes at an operation of Tolerance protect their host-plants from high virulent ones gaining a victory in competition, when infesting of host-plants.

In this context, it should quote D.R. Marshal (1977, p. 10): "…there is a strong negative correlation between the number of genes for virulence carried by a pathogen biotype and its fitness, it is by no means universally true."

Thus, the potent hereditary base of plants resistance in wild grassy plants to phytopathogens – r‑strategists consists in operation CESPPs 2.1.1.3.2. "Tolerance to phytopathogens", and 2.1.1.4.2. "Evasion from phytopathogens." When cultivars have such traits, they are close in their self-protection to wild species that do not decrease agronomic traits of the former.

There is the trend to consider the resistance to phytopathogens as Antibiosis, i.e. to record signs of the affection, and do not notice the traits of Tolerance and Evasion, which manifest themseves by capacity to keep productivity in time and space. For example, M.P. Lisovyi (2001, pp. 22‑23) characterizes the variety Mironovskaya-808 as having no significant resistance to the leaf rust, because numeric score of affection by this phytopathogen is rather low. This variety, however, might be considered as having advanced Tolerance to the leaf rust, because it keeps productivity over a number of decades in diverse environmental conditions.

V.V. Shelepov et al. (2004, p. 432) characterize the variety Myronovs’ka 61 and Myronovs’ka 65 as ones, which “are affected by the diseases in medium level” (to the leaf rust and the mildue), although their grain yield is highest within a list of the shown varieties – 10. 24 and 10.30 metric tons per hectare correspondently. This is a case, when Tolerance is concidered as signs of affection. To the point, both the varieties were bred by V.V. Shelepov.

Wild woody plants also have their heredity untouched by humans. The prerequisite of their resistance to PPs 2.2.2.P.1. "A hereditary ability of a plant taxa (species, subspecies, phenological forms, varieties strains, hybrids, lines) to resist against a given taxon of PPs" is supposed to be proper. It is relevant to compare means of maintenance of their resistance to PPs with those in grassy plants.

In wild woody plants, the durability of resistance to phytopathogens is obviously the same as that in grassy species. In trees, it is known the cases of increase of damage on the part of resident species, and the cases of catastrophic mortality of trees on vast areas up to extinction. The causes of the mass mortality consist in penetrating into the range of a tree species the phytopathogens, which have not been factors of natural selection for this species. The same take place at growing of a tree species in an areas isolated from its natural range, where it is attacked by resident phytopathogens. The latter, again, have not been a factor of the selection.

The examples of such events are well known. The epiphytoties induced by species-invaders are those of the Dutch elm disease, Cerastocystis ulmi (Buismen) C. Moreau, the East American chestnut disease, Endotia parasitica (Murr.) A & A, and the European stem rust, Cronartium ribicola Diet.

Heavy epiphytoties in trees grown outside of their natural range in isolated areas are known for the rust fungus on the coffee tree in Ceylon, West Africa and Brazil, the virus disease on the cocoa-tree in Africa.

In nature, there exist, however, the obstacles to extinction under impact of the high virulent phytopathogens. First of all, this is CESPPs 2.1.2.4.1. "Hereditary heterogeneity of a stock of host-plants." The second obstacle is CESPPs 2.2.3. "Natural enemies of phytopathogens." They suppress virulence of phytopathogens, so that the diseases induced by them get a chronic character, rather than acute one.

Consider some facts, which might be supposed as an impact of indeed natural enemies of phytopathogens. The discourse is given according to Yu.T. D’yakov (1985, pp. 58‑62 and 205‑209).

The Dutch elm disease appeared in Europe in 1918, and over the period more that 30 years killed millions of elm trees. In 1950‑ies, its virulence began to decrease. Newly affected trees ceased to appear, and formerly effected trees recovered. It seemed that the disease became similar to resident phytopathogens, which affected exclusively weakened trees. However, in 1967, it began the second epiphytoty of the disease the same as severe as the first one. The studies showed that this epiphytoty was caused by a new pathotype penetrated from Canada, whereas the first epiphytoty was induced by a pathotype penetrated from China.

What is the cause of the decrease of virulence in the first epiphytoty? The answer has not been found by the author in literature. Nevertheless, the explanation of this phenomenon might be inspired by studies of other diseases. The case is the East American chestnut disease. In these studies, it was found out pathotypes of the phytopathogen of low virulence. When they were inoculated on trees affected by common pathotypes, i.e. of high virulence, these trees began to recover. Further studies showed that the pathotypes of low virulence contained own parasites – virus-like particles, and the recovering of affected trees was a result of a spread of the virus-like infection on a micelium of the high virulent pathotype.

It is logical to suppose that if a hyperparasite appears in a population of phytopathogen, and spread within it, this leads to a decrease of its virulence. This is a hypothetical cause of the decrease of virulence at the first epiphytoty of the Dutch elm disease. The next step is to spread this hypothesis on other invading taxa of phytopathogens.

The chain composed by a phytopathogen (a rust fungus), its parasite (a bacterium) and hyperparasite (a bacteriophage) is known on the wheat and other cereal species (Klement and Kiraly, 1957).

G.E. Russel (1978) has paid attention on the fact that actually all the cases of losses of resistance to phytopathogens are concerned situation, when operate physiological (biochemical) mechanisms of this trait (in the present report, this is the CESPPs A.2.1.1.2.2.2.1.) Such a category of plant self-defense occurred to be less durable than other ones.

Contrary, the structural Antibiosis (in the present report, this is CESPPs A.2.1.1.2.2.1.1.) operates over unlimited time. Probably, the self-protection is especially durable if it consists of a combination of external structures and toxic factors. The protective means of such a principle has been developed by humans. This is the Beaurdeaux mixture consisting of solutions of cupric vitiriol and lime. It uses for spraying of plants before phytopathogen's agents come on plant surface. This preparation has been used over more one hundred years, but the resistance to it in phytopathogens has not been found out yet (Robinson, 1980). As to contemporary systemic fungicides, they become ineffective in not so many years after beginning of usage of them in a wide-scale due to acquired resistance of phytopathogens to the fungicides.

In a breeding process for selection the entries having the most expressed resistance to PPs, it has been used the method of evaluation of this trait in the conditions optimal for an affection. For example, it is practiced growing of wheat entries in areas of tropical climate optimal for activity of the rust phytopathogens. This allows selection of entries with the less affection. Naturally, they have the most potent hereditary base of resistance to these phytopathogens. These are the grounds to suppose that their resistance to them would be durable in less severe environmental conditions. Screening of crop’s entries on PPs resistance in the plots with increased loading by these organisms is bases on the same principle. These measures use the FDESPPs 8.1.5. "Growing of cultivars in the conditions enhancing of SP of PPs."

As to insect herbivores, the theoretical substantiation of durability of Tolerance also has been done. E. Horber (1974) has supposed that the Tolerance cannot be overcome by herbivores at all. This is so because the plants with this trait are not undergone selective pressure on the part of herbivores. The Tolerance neither kills herbivores, nor suppresses vitality of them. It allows to herbivores to reach significant density. In turn, it provokes an activity of their natural enemies, which suppress the hervivore hosts.

Insect defoliators and sap-sucking arthropods are exposed to suppressive effect of weather factors – CESPPs 2.3."Routine weather suppression." Therefore, the evolutionary evolving of herbivores in the case of operation of CESPPs 2.1.1.3.1."Tolerance to herbivores" moves in the direction to counteract these factors of mortality, and to decrease the negative effect on their host-plants. Further, presence of herbivores on plants in Moderate density exert even beneficial effect of these plants by means of enrichment of the soil. The sources of such enrichment are excrements of these herbivores and their predators, especially birds, and bodies of died herbivores. Honey dew of aphids enhances greatly activity of nitrogen-fixing organisms in the soil.

The durability of CESPPs A.2.1.2.1.1."Superevasion from herbivores" is based on the fact that vital activity of plants is possible at lower temperatures than that in arthropod herbivores. Moreover, they strengthen A.2.1.2.1.1. "Superevasion from herbivores" by culling the host-plants with less expression of this trait.

In this context, it should cite I.E. Pavlov (1967, pp. 170‑171), who has reported that many varieties of the barley (Nutans-187, Europeum, Winner, Nossovsky, and others) have been bred many years ago. Nevertheless, their resistance to the flies Oscinella frit L. and O. pusilla Mg. not only remains until now, but even it is increasing. These varieties grow quickly in spring, so that before the beginning of the flight period of the flies, their tillers become hardened. Therefore, the flies’ larvae cannot feed in them. Thus, the flies exert selection of most fast-growing plants of the barley.

The Hessian fly, Mayetiola destructor is an interesting case of sudden appearing as a pest, probably being a native species in the range of its heavy damage in Russia. A.F. Kryshtal (1950) showed that close relatives of the Hessian fly feed on cereal species in humid habitats, whereas the fly feeds mainly in mesophytic habitats on various varieties and species of the wheat, Triticum spp., the rye, Secale spp., the barley, Hordeum spp. and on the couch-grass, Agropyrum spp., in particular Agropyrum repens (L.) P.B.

The change of habitats by the fly and growing of host-plants favorable for ancestors of the fly has been accompanied by forming of species traits and capacity to inflict heavy damage. A.F. Kryshtal (1950) supposes that the family Itonididae (Cecidomyiidae) in the present time is in a stage of abundant species forming.

Consider the issue: what is the cause of differencies in interelations of the Hessian fly with field crops, on the one hand, and the fly with the couch-grasses, on the other hand? In the European part of Russia, the Hessian fly was serious pest of cereal crops (mainly the wheat) over nearly a century. The couch-grasses are common host-plants for the fly. The couch-grasses are wide-spread and tiresome long-standing weeds. The question is why does being favorite host-plants of the fly, the couch-grasses have not been undergone a depression?

This fact implies that the couch-grasses has effective resistance probably of the categories of CESPPs 2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues" and/or 2.1.1.3.1.3. "Tolerance to herbivores, indifference to losses of host-plant tissues." The group of couch-grasses has the trait to store abundant resources in their root systems that allow it to produce seeds in spite of affection of some part of tillers, and to restore their tillers, when affection by grazing and insects colonization. In addition, it is probable the significant role of 2.1.1.4.1. "Evasion from herbivores."

In cereal cultivars, the traits serving as the above CESPPs are expressed less. Therefore, Mayetiola destructor endangers them more than the couch-grasses.

As an example of longevity of CESPPs A.2.1.2.1.1. "Superevasion from herbivores", it can serve the usage in North America until now the optimal (late) sowing dates of the winter wheat for protection against the Hessian fly. This measure is practiced over a hundred of years, but still is effective.

In woody plants, the CESPPs 2.1.1.2.1.2.1."Antibiosis to herbivores, Physiological (biochemical), Permanent" is quite durable. Long co-evolution of woody plants with their PPs has led to development of exclusively multilateral traits of self-protection of assimilative tissues in coniferous species and vascular tissues in all the woody species. The protective product of coniferous species – oleoresin consists of up to fifty toxic for PPs substances. Also eucalyptes are protected by great diversity of adequate substances. In volatiles of their foliage, it has been found out about 270 organic compounds probably of a protective concern (D’yakov, 1985, pp. 79‑80).

Nevertheless, it is necessary for self-protection of coniferous tree species something more than only the presence of toxic substances in tissues. In fact, in tissues of weakened trees, the content of oleoresin is the same as that in healthy ones. This does not provide an obstacle for numerous species consuming coniferous species. The difference between healthy and weakened coniferous trees consists in a capacity of the former to convey oleoresin to attacking herbivores or to wounds that protects them against phytopathogens. In a result, attacking PPs occur inside a toxic and viscous product, whose amount is much greater than a mass of herbivore bodies or agents of phytopathogens. On the air, oleoresin becomes solid. Under such a complex effect, even rather large beetles die. Killing of bark beetles in oleoresin on a stem surface (in pitch tubes) or in bark of their host-trees is a common event. The same takes place at attacks of healthy treea by other stem borers, For example, A.S. Rozhkov (1982) reported about mortality in exuding oleoresin up to 70% larvae of the longhorned beetle, Xylotrechus altaicus Gebl.

The great variety of protective substances in coniferous and eucalyptes species suggests that their resistance has indeed polygenic character. This is the case of the factor durability.

An additional obstacle for surviving of PPs in coniferous species consists in diversity of composition of turpentine within a species. Among samples of turpentine taken in trees a plot, there are no the trees having the same composition. Therefore, in such ecosystems, it operates CESPPs 2.1.2.4.1. "Hereditary heterogeneity of a stock of host-plants."

The complicated composition and peculiar physical properties of oleoresin hamper to consume this product. It is free of consumers with the exception of the little group of insects, which are called "resinocols" (Mamayev, 1971). They need to pay for feeding such an uncommon foodstuff by slow development and high mortality that result in Low density.

The ecosystems of coniferous tree species, where conductive and assimilative tissues concerned the biomass D‑I, they are propected from PPs by CESPPs 2.1.1.2. "Antibiosis."

In woody deciduous tree species, CESPPs 2.1.1.2. "Antibiosis" operates only in conductive tissues. This is the biomass of the category D‑I. In the biomass D‑II of these species, it operates CESPPs 2.1.1.3."Tolerance" and being in a cooperation with CESPPs 2.2."Natural enemies", 2.3."Routine weather suppression", and 2.4. "Periodic (bottle-neck) suppression." These CESPPs provide durability of ESPPs on the level 3.1. "Proper control" that is demonstrated by flourishing of these ecosystems, if they have not been disturbed by humans or natural force-majeur impacts.

As to the defoliators, which inflict insignificant damage for host-trees, it is tolerable a decrease ESPPs to the level 3.2. "Lag control" by CESPPs 2.1.2.1. "Superevasion" or 2.1.1.4. "Evasion" in a cooperation with other CESPPs, so that these categories of host-plant to PPs also provide ESPPs with durability.

The hereditary prerequisite of all the subcategories of the in wild woody plant species retains in all the circumstances, except the cases of invasion of species-strangers and growing of tree species outside of their natural range.

To summing up. The durability of ESPPs is provided by diverse CESPPs on condition that their hereditary prerequisite is proper. Depending on the category of biomass, these CESPPs are the following:

vi) On biomass of the category D‑II (assimilative tissues, tillers), CESPPs 2.1.1.3. (A.2.1.1.3.) "Tolerance" (diverse subcategories) and CESPPs 2.1.2.1. (A.2.1.2.1.) "Superevasion" or 2.1.1.4. "Evasion."

vii) On biomass of the category D‑I (vascular tissues, assimilative tissues in evergreen coniferous species and in the eucalyptes), 2.1.1.2. "Antibiosis", and 2.1.1.1. "Nonpreference."

These points correspond to understanding of the durability of plant resistance to PPs as having the polygenic (horizontal) character. The suggestion as to durability of monogenic (vertical) resistance needs to be proved. When operating with plant resistance to PPs, it should, however, follow the phenotypic display of this trait, rather than by speculations as to the number of the genes being engaged.

The practical implications from these speculations are the following:

viii) It needs to evaluate plant resistance to PPs (CESPPs A.2.1.) in the provocative for PPs environmental (laboratory and field) conditions. Importantly, it should take into account not only numeric scores of affection, but also values of crop’s yielding, practicing the pesticidal check.

ix) It needs to maintain CESPPs A.2.1. of a cultivar by artificial selection of resistance plants in conditions of increased infectious loading at seed farming.

It should recall that CESPPs 2.1. (A.2.1.) “Plant resistance to PPs” is durable on condition that the presence of the following prerequisites:

2.1.1.P.1. (A.2.1.1.P.1.) A hereditary ability of a plant taxa (species, subspecies, phenological forms, varieties strains, hybrids, lines) to resist against a given taxon of PPs,

2.1.1.P.2.(A. 2.1.1.P.2.) Level of physiological state of a host-plant, which is close to proper one.

2.1.2.P.1. In biocenoses, forming of a dominant stock at the natural conditions.

A.2.1.2.P.2. In articenoses, a resemblance of a dominant stock to that in biocenoses or special cultural practices with the aim of effective operation of CESPPs A.2.1.2.

8.2. Anthropic-2

8.2.1. Cultural practices disturbing physiological state of dominants and obstacles for host-plant superevasion


2.1.1.P.2. A level of physiological state of a host-plant, which is close to proper one

2.1.2.P.2. In articenoses, a resemblance of a dominant stock to that in biocenoses or special cultural practices with the aim of effective operation of CESPPs A. 2.1.2.

8.2.1.1. CESPPs 2.1.1.1.1.3, 2.1.1.2., A.2.1.1.2., 2.1.1.3.1.2., A.2.1.1.3.1.2., 2.1.2.1., and A.2.1.2.1. failed


R. Painter (1951) has considered the resistance of trees to pest insects as a special category of this trait – a physiological resistance. It might be this view is a reflection of the fact that the proper physiological state of trees as a prerequisite of resistance in forest trees occurs to be disturbed very often.

The causes, why silviculture concedes agriculture in maintenance of the proper physiological state of plants, consist in two realities. Firstly, it is difficult to control the state of perennual trees growing often in environmental conditions far from optimum for a given tree species. The second, in agriculture in field, defects of cultural practices become obvious in the same year or within few years. Therefore, the defects of cultural practices can be revealed easily.

Contrary, in silviculture, the improper cultural practices bring their fruits often through dozens of years. Obviously, it is difficult to reveal true causes of weakening of physiological state of these, if the grounds of that were laid many years ago. In this human activity, articenoses with improper composition of plants are often established, so that the prerequisites 2.1.2.P.. and 2.2.1.P. become disturbed that lays obstacles, in particular for operation of Superevasion and activity of natural enemies.

Due to above peculiarities of silviculture, the cultural practices in this province are characterized by the vast number of defects. It is necessary for growing of healthy forest to bring the defects on light. On the other hand, over centuries of its existence, forestry has developed measures, which allow establishing stable forest ecosystems even in severe environmental conditions. Unfortunately, the achievements of forestry often are not used in practice.

In silviculture, FDESPPs 8.2.1. "Cultural practices disturbing physiological state of dominants and obstacles for host-plant superevasion" includes a wide diversity of activities and operates in complexes with many other FDESPPs composing diverse combinations, in particular with 8.2.3., 8.2.4., 8.2.5., 8.2.6., 8.2.7., 8.3.1., 8.3.2., 8.3.3., 8.3.4., 8.3.5., 8.3.6., 8.4.1., 8.4.2. Therefore, later in this text, it will be numerous returns to this FDESPPs, when considering of a cooperation of FDESPPs and their complex effects.

Because the management in agriculture is controlled much better than that in silviculture, the cases of improper cultural practices in the former are rather rare. Nevertheless, the affection of the winter wheat by the frit fly, Oscinella frit due to improper cultural practices have been demonstrated by G.I. Vasechko (2001). In the one case, the winter wheat was grown in the special test with the diverse practices. In plots with surface tillage instead of digging up and absence of fertilization, value to tillering occurred to be low, percentage of tillers colonized by Oscinella frit was much greater than that at proper cultural practices (normal digging up and fertilization).

In the other case, the winter wheat was sown the large delay and on the exhausted soil (after harvesting of the sugar beet). These circumstances resulted in the same effect as that in above example. It had to re-sow this field.

These examples suggest that in agriculture, maintanance of the level ESPPs A.3.1."Proper control" needs in strict providing an operation of prerequisites of CESPPs A.2.1.1.3. and A.2.1.2.1. "Superevasion" both against herbivores and phytopathogens. The usage of optimal sowing dates of winter and spring crops allows decreasing of density of herbivores and affection by phytopathogens to the Insignificant values.

8.2. Anthropic-2

8.2.2. Changes in the soil conditions unfavorable for dominants



8.2.2.1. CESPPs 2.1.1.1.1.3., and 2.1.1.2.1.2. failed

8.2.2.1.1. Outbreaks of stem borers

The disturbance of physiological state of plants is common at sharp change of water regime of the soil. The changes take place at building of large water reservoirs (storage lakes on rivers) and drainage of swamps. The reservoirs induce a lifting of the water table, which exerts destructive effects of forest sometimes on dozens kilometers outside of them. In a result, roots of the trees growing in depressions occur continually in the water and die off. The mortality of dominants takes place in riparian forest growing on banks above dams in river’s valleys. Below dams, riparian forest suffers due to cessation of flooding. Such causes of physiological state of trees operate, in particular in Ukraine in vicinity of the River Dnieper. On this river, it has been built several giants reservoirs, which established a number of problems of the above-mentioned character. After building of the grandiose Kakhovka storage lake on the River Dnieper, the water table on the level side of the Dnieper Valley rose on the distance thirty km for fifteen years (Skaballanovich et al., 1979, p. 163).

The dieback and decline of trees are common on edges of a forest with clear-cut areas in the humid habitats. Until integrity of a forest massif is not disturbed, the water table stays on admissible for tree vitality depth, because trees draw off water from the soil. Contrary, after clear cutting, a water table lifts on the soil surface, and a clear-cut area becomes a swamp. The latter spreads in a near by forest, and trees in the range of a swamp die off.

At drainage of territory, a water table brings down and stays continually on a low level. In Soviet Union, digging of trenches in swamps and humid forests was practiced often. The grounds of such activity consist in an intention of the powerful Ministry of Melioration to have objects, which prove necessity of existence of this monster.

At absence of drought over several years after digging of the trenches, the trees are able to spread their roots to the lowered level of the water table and to survive. Contrary, at drought in this period, the roots dry out and the trees die.

8.2. Anthropic-2

8.2.3. Damage of dominants by people or animals under human assistance



2.2.2.P.1. Proper activity of predators, which operates in cooperation with CESPPs of the category 2.4. Periodic (bottle-neck) suppression

2.2.2.P.2. A size of area of an ecosystem sufficient for providing of predators with vital requirements

8.2.3.1. CESPPs 2.1.1.2.2. ,2.1.1.1,1.3., 2.1.1.2.1.2. , and 2.2.2. failed


A mechanical control of weeds, which is conducted in afforested areas annually until closing of their canopy, it is common damage of young stems. Again, these wounds serve as an entrance for infection. Therefore, application of herbicides is prospective for control of weeds.

The heavy techniques, which are used for withdrawal of cut trees, exerts damage of roots of reserved trees and wounds their stems. The damage is most destrictive, when tree cutting is conducted in warm period of year. In Tsarist Russia, it was conventional to conduct all kinds of wood cutting in winter. In Soviet Union and Former Soviet Union, all kinds of wood cutting are conducted the whole year round. In so doing, timber becomes endurable to rots.

In forests, which are often visited by people, for example those of a recreative concern, it is common suppression of vitality of tree’s roots due to trampling down of the soil, that result in dieback or mortality of trees.

As to wild hoofed animals, a lack of their predators and insufficient hunting lead to heavy damage of young trees. In addition, the great damage is inflicted by cattle. Grazing of cattle in forest is practiced widely in this country. Protection of a young generation of forest from the grazing is limited by plantations until closing of their canopy. After that, cattle is able to penetrate into plantations freely. It is supposed to be this is the main cause of affection of oak stems with the stem cancer, which produces large tumors (Rudnev et al., 1975).

8.2. Anthropic-2

8.2.4. Affection by air pollution


2.1.1.P.2. and A. 2.1.1.P.2. A level of physiological state of a host-plant, which is close to proper one

8.2.4.1. CESPPs 2.1.1.1.1.3., 2.1.1.2.1., A. 2.1.1.2.1., and A.2.1.1.2.2. failed

8.2.4.1.1. Outbreaks of stem borers in forests and signs of diseases affecting agricultural crops

Now, it is not popular to explain the forest decline by weakening of forest at improper silvicultural practices. The main cause of the decline is supposed to be air pollution. This idea may be seen in the quotation from W. Baltensweiler (1985, p. 77): "The risk of outbreaks of bark beetles and forest defoliators is enhanced in polluted ecosystems, either due to the reduced vigor of the trees and/or altered characteristics of the host-plants. The long lived trees are at a selective disadvantage, therefore air pollution must be stopped and any insect impact, which generally accelerates the "Waldsterben" should be avoided" (p. 77, Summary).

The role of air pollution comparing with other stressors is, however, unclear that may be seen in the following quotation: "Since World War II repeated outbreaks, snow breakage and air pollution combined caused the destruction of more than 100 000 ha (Wentzel, 1982)" (Ibid., p. 81). This phrase suggests that "repeated outbreaks, snow breakage and air pollution" are independent phenomena."

As to conversion of mixed beech-silver fir forest into overstocked spruce monocultures and exhaust of soil resources at withdrawal of wood biomass, when cutting mentioned in the cited paper, this is an obvious cause of repeated outbreaks and snow breakage in Middle Europe. Contrary, the role of air pollution in the wide-scale forest decline is not obvious.

It seems air pollution has become idèe fixe at explanation of the forest decline. It should stress that effect of air pollution is well detected by its location in vicinity of large industrial enterprises. Further, it is characteristic for countries of the Former Communist Block, where authority ignores protection of the environment.

As an example of such a situation, it can serve the report by V.V. Fomin and S.A. Shovnin (2001). The studies were conducted in a region of a copper-melting plant in the Sverdlovsk Region (Russia). It was shown that the heavy affection of forest spread eastward the plant - up to 20 km as an entire area. Farther, signs of the affection were recorded in separate plots of fewer areas. This disposition of the affected areas was due to the direction from the west of the prevailing winds in this area. Westward the plant, the affection spread only on 5 km.

This report is consistent with the view by W.H. Smith (1981). He has supposed that "Severe impact of air pollutants on forests are dramatic, but judged relatively unimportant because of their extremely localized nature" (cited in W. Baltensweiler, 1985, p. 77).

In the publication, which probably expresses the view of United Nations Organization, the pollution, although of another kind, is considered as the only cause of Waldsterben in the industrial countries (Horstkotte, 1995). This pollution is of the kinds of exhaust gases and spoiled subsoil waters. Such pollution is important as to human health, but its concern to Waldsterben is dubious. If this view would true, mortality of trees would affect first of all shade trees in settlements and road-side plantings. However, Waldsterben takes place just in exploiting forests, whose state is determined by silvicultural practices independently on distance from the exhaust gases and spoiled subsoil waters. The polluted subsoil waters cannot penetrate in mountain forest, which often undergoes the decline, in particular in Germany. The exhaust gases are hardly are able to kill the trees in remote mountain forest. Being such poisonous, the gases would depopulate all the settlements.

Again, the measures, which have been proposed in the above article to counteract the forest decline, are wrong. The measures are limited by a decrease of output of carbon dioxide (Ibid., p. 2). Firstly, the issue of carbon dioxide output is neither air pollution, nor subsoil water pollution. Secondly, the dependence of severity of droughts on output of carbon dioxide is very dubious. Here are examples of a lack of the dependence. In IX‑XI centuries, the technology was too weak to effect on climate. Nevertheless, climate in the region of North Atlantic was warmer than that now. Contrary, XVI‑XVIII centuries are known as the Little Ice Age. In the peak of the cold and wet period, when size of glaciers in Switzerland reached maximum, and the Rhone River is south France was caught many times by ice (1556‑1595). In the same period, the western areas of North America suffered due to the severest drought. It continued over twenty years (1570‑1590), and the values of precipitation composed over 20% of those typical for XX century (Le Roy Laburie, 1971, pp. 213‑215). Notably, that the sequoia trees, which at present time are close to 1000 years old, have survived this stress, as well as the forest biome as a whole.

Further, air pollutants can serve as nutrients for plants. Here is the citation from D.P. Ormrod (1978, p. 22): "White pine seedling productivity increases with decrease in pH of simulated acid rain from 5.6 to 2.3. in spite of near depletion of available K, Mg and Ca ions in the soil at pH 2.3. (Wood and Bormann 1977). Additions of HNO3 to the simulated rain are associated with increased foliar N concentration."

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