Persistence and regeneration mechanisms in forage...

Persistence and regeneration mechanisms in forage legumes

Sulas L., Franca A., Caredda S.

in

Sulas L. (ed.). Legumes for Mediterranean forage crops, pastures and alternative uses

Zaragoza : CIHEAMCahiers Options Méditerranéennes; n. 45

2000pages 331-342

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Sulas L., Franca A., Caredda S. Persistence and regeneration mechanisms in forage legumes.

In : Sulas L. (ed.). Legumes for Mediterranean forage crops, pastures and alternative uses . Zaragoza :

CIHEAM, 2000. p. 331-342 (Cahiers Options Méditerranéennes; n. 45)

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Persistence and regeneration mechanisms in forage legumes

Sulas', A. Franca' and S. Caredda2 di Studio sui Scienze e

Genetica vegetale via E. Nicola, 07100

Summary - an of legumes, is influenced by climate, management, pests, and by in a given The main mechanisms of in the

of annual legumes, its Seed ability, seed and pod and seed and with animal

ingestion and of is typically based on the vegetative even though seed can be also involved. and ecological adaptation of to one of the following 1) of a deep system and woody due to the of the plants; 2)

of stolons which can the plant has died and 3) by the of can affect the legume such as

management, adaptation capacity of species and its simbionts, to fungi and insects. the legumes potential has not been fully exploited new such as the

legumes" available. being made in developing legumes.

annuals, seed vegetative

- La pérennité, attribut essentiel chez les légumineuses fourragères dépend du climat, de la gestion, des maladies et de leur interaction au sein de l'environnement. Les principaux mécanismes de la reproduction sexuée des légumineuse annuelles sont ceux qui contrôlent la germination: la dynamique de la banque de graines, le tallx de graines dures et les modalités de levée de la dormance. La capacité d'enterrer ses graines, de les disperser et les caractéristiques de la gousse et des graines par rapport au mécanisme d'ingestion et d'excrétion des animaux sont aussi très importants. La pérennité des légumineuses vivaces est basée sur les mécanismes de reproduction végétative même si certaines se régénèrent également par graines. Trois stratégies d'adaptation ont été développées: présence d'une racine pivotante profonde et d'une structure ligneuse persistante, 2) production de drageons capables de swvivre h la mortalité du pied-mère, 3) formation de rhizomes. D'autres facteurs tels que la gestion, la qualité de l'association symbiotique, la résistance aux maladies influent sur la pérennité des légumineuses. le potentiel des légurnineuses n 'a pas encore été pleinement exploité et de nouvelles sources de fourrage à partir de légumineuses sont régulièrement proposées. De gros efforts doivent être entrepris pour développer des pâturages durables à base de légumineuses.

légumineuses, banque de graine, graines dures, dispersion, régénération

absence of all of success of legumes, such as quality, etc., meaningless (Cm, to Smith (1989),

is "the of plant against specific unique to the existing definitions include also the aspect of time in

a given in addition to the maintenance of of seedlings (annuals) viable at the end of the

of white is defined as the the and fifth

33 1

CIHEAM - Options Mediterraneennes

seasons and yield of evaluation and 1995). In addition the legume content in the and the also as stand indices. legumes is influenced by plant genotype, climate, pests, management, ecological situation and especially by Since these among is a complex and highly specific

this some of the main aspects and affecting discussed with emphasis on the most annual and legumes.

Seed constitutes both the and the end of the life cycle of annual legumes and its is an obligate mechanism. The key of

annual legumes that sufficient seed must be and that of should adequate seedling at the onset of the

following wet season, and that these seedlings to and set seed. addition, a of seed must than one because unsuitable

conditions (e.g. absence of etc.) management may seed set in one an ecological point of view, seed

seed seed and seedling the key the adaptation of species to any climatic (Cocks, 1997a).

Time to jlowering and maturity a given the phase should take place enough

adequate seed set to advent of of the climatic and among the of annual legume species

the and even in 1993). aspects of of to obtainment of viable seed,

of of and of seed of Trifolizim subterranean and annual medics in to daylength

and but in to these addition can delay initiation and annual medics than

time is the most of all to changes as shown by the in of the same in

instance, in of is delayed to and the in time between the same

and Seaton is less than 10 days with about 30 days in 1993). and Gladstones (1974) found that and

of T. subterranezm seeds than long and in the basin, ecotypes that a have an advantage in the season ends 1993). with in and seed yield of a

may be a may again conditions. to and (1997), within

with date), a by and seed is in with a and seed because the stage when climatic conditions

so allowing seed yields. in with a good soil content the vegetative cycle, the pathogen and attacks on the seeds of while late able to escape

damages and to exploit late Selection time has allowed to extend cultivation of annual legumes.

332


in subterraneurn was less than seedling density at the of the season obtaining high availability in autumn (Carroni et al., 1995). On the

some of as in fast establishment and life cycle to that of the also

uses, such as lines, etc. et al., 1995). Seed bank

Seed bank is defined as "a of viable seeds in the soil and on its et al., 1992a). The

of seeds in the soil is by seed and depleted and which seed the bank: in situ, a (ii) plants displaced in time space so that the the soil seed bank by a of mechanisms, and (iii) sowing by man to meet objectives, even though the also apply to these they have been established 1987).

with annual annual legumes can have a seed individual seeds may live fact, these species

seed in and only a of that seed in the following autumn. This allows the species to escape and high

to occasional failed to still maintain seed viability.

The size of a soil seed bank and its changes to inputs and past of plants and also to season and management (Loi et al. 1999). In these changes depend also on the seed consumed by animals. the seed bank has an ecological because its

of plant density, which affects the its botanical composition et al., 1992a; 1992b). Hardseededness an.d other mechanisms regulating germination

to in the soil, seeds must not only also not to is a physical exogenous caused by the

of the seed coat that maintains the quiescence of the seed imbibition with Seed coat is to the of a

the the of this thickening is influenced by genotype, conditions the season of the 1993; 1993).

due to both and genetic is of significance legume Ewing, 1988). is the most "long

in legumes because it maintains the seed bank to may may not of The level

od widely among species. instance, in seeds the soil 2 it about 90% in Biserrula pelecinus and Ornithopus compressus to about 10% in T. subterranezm (Loi et al., 1999) negligible values in O. sativus whose seeds completely soft. the the use of species with and soft seeds can to legume stability time.

To the of softening is than the initial level of seeds. The evolution of the same

accessions of polym,orpha changed to to the conditions et al., 1996).

wide fluctuations play an in (softening) of species adapted to

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mediates seed (i) the heating effect of on the of soils (insolation) coupled with night-time cooling, and (ii) the but intense heating of the soil caused by manmade 1992).

to (1981), softening of T. subterraneum seeds in two stages: a of high a of

(60/15 "C). met in soil and as a most of the seeds become soft by autumn, when false is still high.

this case, the is used. seed in slow than in pods: the softening in may fall if seed is

10 cm and Ewing, 1988). Cultivation may also affect seed softening. (1985) of in the following minimum tillage as with conventional tillage, although the of seed by conventional cultivation in of seed.

with T. subterraneum, the softening of O. compressus seed was when 2. cm below the soil than when left on the soil while in B. pelecinus was (Loi et al., 1999). These species have

seed softening: T. subterraneum high in the second stage of seed O. compressus and B. peleciuzus a high heat

input in the stage. Seed softening of annual medics in the vicinity of 35/10

"C these do not until late autumn, the loss of of these species is delayed in to T. subterraneum. In addition to seeds of exhibit: (i) a physiological

due to an and (ii) a physiological due to unsuitable ambient that that would be insufficient to the of seedlings (Quinlivan, 1971) to the

of an seedcoat and 1995). fact, seeds can in the soil 14 days without loss of

viability. is not as as in of at high in many

(T. resupirzatum, T. subterranean, T. michelianum), due to the maintenance of (Cocks, 1997b), while can continue at

mechanism is slow until effective soil is (e.g. T. clypeatum). point of view, it can be useful to seed the

objective of the establishment of legumes seed in Seed of ciliaris and rugosa exposed to mechanical, physical and chemical

to identify the which and the actions to it and 1993). in liquid

the most effective in The two species to the same due to in thickness of

the cell of the seed coat, as by using an Seed burial, dispersal and predation

Some species seeds, so limiting the to the base of the plant The success of T. subterraneum, as a species, is linked to its ability to

pods, escaping the effects on seed bank size et al., 1985). The ability of the same may to soil and

the viable seeds. peduncles and thick in T. subterraneum, they and less in T. brachycalycinum; the does not any lines of T. subterraneum and T.

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brachycalycinum examined to assess the and depth of the the amount of developed 21 days anthesis. The high

between species seem to which associated to distinct edaphic specializations. subterralzeum has a

ability, which is the development of its and is common in sandy and soil; T. brachycalycinum instead is in and clay soils. As the

ability 1995a). an complete of seed by the soil with a plastic film, caused a

of seed yield in both species, the effect was slightly in T. brachycalycinum 1995b). in ability within species is also against insect pests. Bruchidius trijolii a in the

basin but not in 50 to 100% of T. braclzycalycinum seeds (not in field et al., 1993). This

both the seed bank and, consequently, the legume capacity, despite a seed of 4,500 seeds m-2 in the the

seed damage to of T. yanninicum was negligible. Amphicqy is the of and and pods in the

same plant (e.g. Vicia sativa anzphicarpa, vetch; Lathyrus ciliolatus). vetch is common in of West Asia with 250 mm of

et aZ., 1996). This species both pods, containing 5-7 seeds, that seeds the plants, 1-2 plant. These and being maintained in the same place they

seed by insects plant type and habitats. example it 2-6% in Vicia sativa to 39% in Ovzobvychis viciaefolia In

seed by insects. The movement of seeds a plant to the seed

seed and mechanisms by the by elements to the coat of animal, (ii) ingestion

by and by such as ants. The significance of elements in seed depends on the species

climate and of the site. When seed comes into contact with the soil, can continue with of

in the lodgement of seeds. Light can be by wind, but this kind of is less

because the legume seed is dense and usually without appendages such of Spiny pods and seeds of annual legumes can be to

hooves, hides and wool, and by ingestion and subsequent in thefaeces of animals. characteristics, seed size and ingestion by ruminants

Legume is affected by both and to should management

should the of seeds. it is to define a of by which is

small pods less easily selected sheep than pods. At the same time, even though the ones in the soil, they subjected to

by ants, which an example of causing losses seed into the seed bank the soil seed bank.

to is the single most significant weakness in annual medics whose high quality pods, with about 20% of feed the

335


sheep stubble the season (Sitzia and Fois, 1999). The ability to of small, seeds, to the ecological success of legumes

in 1997); than seed weight, but seed species will depths. Seeds eaten by livestock mostly digested. a of seeds ingested by small

is able to escape and is thus to the seed bank. The of ingested legume seeds that passes undigested has been with the animal species, seed size,

intake, digestibility of the associated diet, amount of the seed consumed etc. Small seeds likely to avoid mastication and because the the seed size is, the the of the passage the digestive of animal is. to Thomson (1990), seeds than 2 mg unlikely to in while up to 60 % of seeds than 1 mg will seed ingestion is in sheep, which a of ingested seed, than in cattle, but likely to most space of seedlings.

1993) have shown that the fate of the seed in a T. subterranezun follows: ingested and digested, depending on

and animal species; 3-18% ingested and viable to the soil; 14- 20% stocked in the seed bank seed; seedlings at the following

and 2-5% lost. The passage of legume seeds the digestive of cattle and in faeces was studied a ingestion by

et al. (1993). of the legume seeds was dependent on the of seed in the sample. Wide in sekd time to be due to

specific (density), of seeds and seed size. the digestibility of legume seeds was to

Small seed size is, at the same time, a potent method of and an efficient mean of seed by faeces. by livestock has been suggested

some as a way to species inaccessible Sixteen native legumes belonging to Trifolium, and Scorpiurus

in passage the animal; the of sheep in legume seeds one the same legumes to an un-

was also studied (Ghassali et al., 1997). seed ingestion 72 and it 70% T. campestre and T.

tomentosum, 20% medic species and 2% H. unsiliquosa. The to the seed by sheep to the was the small seed species

(i.e. Trifolium).

Vegetative regeneration and persistence of legumes

and ecological adaptation of legumes to development and is typically based on the vegetative

of the plant, but seed can also on legumes can be divided in

classes: l ) Species with a deep system depends on

of L. is based on its deep system in plants and soil types. The is by at

the base of the plant, just above the and the main of defoliation. Although defoliation is followed by a the

the of the plants.

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subsequent build-up of is slow. defoliation in depletion of and eventual plant death. and quality,

accumulation and of affected by management and 1987) and by susceptibility to diseases. Usually is cultivated

may photoassimilates and less in than and

could be susceptible to with of et al., 1992).

Trifolium pratense is used as an to because of its to low and acidic soils. has been as a which

its yield in the establishment. to obtain optimum and yield, T. pratense should be 3 times a when plants

between the bud and 20% bloom stage et al., 1998). Light medium defoliation intensities at the bud phenological stage allow an

acceptable stand of Olzobrych,is viciaefolia and 1991). The effective coexistence of a double mechanism in sulla (Hedysarum

coronariunz L.), a When sulla plants have not seed, due to hay cutting autumn will not only of

plants but also new seedlings, a soil seed bank is On the when sulla plants have seeds, the mobilisation of the

can cause weakening and death of leading to a in a low seed can be caused by the high amount of seeds in the

if is a lack of and seed. that sulla has a capacity to be exploited in to its plant

(Sulas et al., 1999). An management, aimed at a mininzum seed set in the sowing, seems to be the only effective way of the

of the sulla meadow. 2) Species clonal patches of stolons which can the

plant has died. T. repens (white the stolon is the basic unit of the plant; of

stolons involves adventitious development which allows these stolons an individual existence when the seminal system dies. the negatively of stolons and the ability of stolon apices to defoliation to the success of white as a legume. the capacity to develop independent systems each a the of white in intensively

systems, as it enables the species to and even following of plants by defoliation to the constant of nodes, white is

a species with a system and a low that affects negatively the and hence usefulness of white in

white is able to by maintaining an adequate of live stolons to the stand via stolon tips. that of the basal of the stolon die, while the end alive to new in the fall. fungal diseases may white

stolon and 1995). and its with studied in

populations and of "Ladino" white at Lodi and 1995). populations showed than The

of ecotypes was positively associated with stolon density, yield in the and length, while it was to seed yield and its components.

337


and of white is also possible via establishment seed. plant canopies open, white may as an annual 1966). The

and of T. repens seedlings deposited seed 3 management and sites in New Zealand (Chapman, 1987). Only

4.4% of the seedlings and established, plants, a mean of one seedling 5.5 Such a low indicates that seedling plays only a T. repens in that

the maintenance of genetic within the stolon populations occasional seedling establishment should be as having an

ecological 3) Species that both and by the of adventitious

The habit and the (development of new shoot of two mechanisms that allow its and its

et al., 1995). In fact is by the emission of which allow plant to and

and conditions than The and of to the

conventional one, to a climatic conditions so plant Chabaane and 1995). a quite stable

content and is in even if its and than those of the conventional one.

Trifolium ambiguzrm is a legume with a habit that an excellent to is to that of most

except of the stock may as much as l m in unusual of this species is its in (2.74 vs T. repens). T. ambigzkum is a new legume and, due to its extensive and development, has the potential to be a

most of the commonly used legumes non continuous in of heat and So T. ambiguum a novel legume to of due to lack of disease susceptibility, sensivity to close defoliation in USA and Smith, 1998). the of Caucasus, it has been in

of the succeeding also in such those in The of T. ambigztum is its longevity; in the high of Southeast it has up to 17 The extensive and systems of established stands

the ability to maintain an adequate of total a of defoliation

Galega orientalis Lam galega) is a quite new of excellent quality all kinds of domestic animals. galega is

a (up to 60-100 cm) which and also vegetatively with stolons (Nommasalu and 1996). These stolons in

soil up to 10-30 cm new shoots and developing additional Then, the young shoots become independent plants. these galega is a and species.

shoots system in addition to the initial

Other factors related with legume persistence and future perspectives

addition to the mentioned (e.g. tillage and etc), can affect legume The adaptation capacity of

33 8


legumes and its simbionts and to diseases and insects also fundamental in instance, the ability of to

in the absence of its legume host is a successful establishment and systems. The lack of nodulation in new

cultivation can legume legumes have developed adaptation mechanisms to and climates potential has not been fully exploited yet. fact, new species with potential, such as the legumes" in with and medics, being

These species have been successfully cultivated and New Zealand and could be used in edaphic and niches. some specific species such as the deep system of Lotus purhsianus, should be effectively exploited both in conventional and legumes.

legumes in even if, heavy annuals dominant and 1998). they have

not been extensively investigated yet. is a to exploit the genetic of legumes, of those species that able to escape

and to associate vegetative with ability. fact been made in developing legumes. Some example

of these the selection types of to to and cold specific time of

cultivation to seed yield and ability in T. subterraneum, seed level at the end of to diseases, etc.

Finally, cannot be taken into per se but only in of all success of legumes, and a knowledge of the mechanisms

and affecting (e.g. ingestion by of etc.) should be achieved and at level to set up an management of legumes.

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