Phacidiella discolor (Mout. & Sacc.) Potebnia in England 8r

to Miss E. M. Wakefield, MissL. Solberg, Dr G. H. Pethybridge,Dr R. M. Nattrass and Mr W. C. Moore for cultures and forassistance with literature.

SUMMARY.

The occurrence of Phacidiella discolor (Mout. & Sacc.)Potebnia in England is recorded, associated with a die-backand canker of apple trees, as described in a recent paper on thepycnidial stage of this fungus by Southee and Brooks o). Thefungus also causes a black rot of apples in storage.

Cultural work has shown that F. conspicua Marchal, andprobably also" Pyrenochaeta furfuracea" (Fr.) Rostr., is identicalwith the pycnidial stage of Ph. discolor.

Further information is given about the growth of the funguson culture media.

The synonomy of the fungus is considered.

REFERENCES.(1) SOUTHEE, E. A. and BROOKS, F. T. Notes on a pycnidial fungus associated

with a dying-back of apple branches. Trans. Brit. Mycol. Soc. XI (1926),213.

(2) POTEBNIA, A. Ein neuer Krebserreger des Apfelbaumes Phacidielladiscolor (Mout. et Sacc.) A. Pot., seine Morphologie und Entwickelungs­geschiehte. Zeit f. Pflanzenkrank. XXII (1912), 129.

(3) MARCHAL, E. and E. Contribution a l'etude des ehampignons de Belgique.Bull. Soc. Bot. Belg. LIV (1921), I.

(4) OSTERWALDER, A. Phacidiella discolor (Mout. & Sace.) A. Pot. als Faulnis­pilz beim Kernobst. Centralbl. f. Bakt. II, LII, 374.

(5) RosTRuP, E. Plantepatologi, p. 571. 1902.(6) VON HOEHNEL, F. Fragmente zur Mykologie, XIX Mittheilung, Nr 1001

bis 1030. Sitzungsber. K. Akad. Wiss. Wien (Math.-Nat. Kl.), CXXVI(1917), 283.

SUCCESSIONAL DISEASE IN THESCOTS PINE.

By Malcolm Wilson, D.Sc., F.R.S.E., F.L.S.Reader in Mycology, University of Edinburgh.

IT is now generally recognised that in combating disease,investigation of the predisposing conditions is of great import­ance, and may even be of as much value as the study of a causalorganism, especially so when the diseased plants cannot bereadily treated with fungicides either on account of their sizeor situation or because the cost involved would be greater thanthe increased value of the crop resulting from such treatment.For the latter reason treatment of diseased trees in the forestwith fungicides is rarely or never carried out on a large scale,

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82 Transactions British Mycological Society

although it may be resorted to when it is desired to save alimited number of trees. When it is necessary to check thespread of the disease, destruction of the diseased tree togetherwith the causal fungus is usually the only method possible.

The fact that the predisposing condition for the developmentof a given disease may be brought about by the previous attackof some other organism is well known, and numerous instanceshave been described in plant pathology. As an instance of fungaldisease following previous attack by another fungus, the infec­tion by N ectria galligena of scab wounds produced by Fusi­cladium dendriticum as described by Wiltshire (9) is a particularlyinteresting example and numerous cases of fungal diseaseconsequent on insect attack have been investigated.

Attacks by a series of parasites in which each organismcreates the necessary predisposing conditions for the followingone have not been described so frequently, although they areof great interest and often of considerable importance. Theexpression" successional disease" may be used to describe casesof this kind. Finally, cultural operations, especially if badlycarried out, sometimes predispose to certain diseases and here,if disease is to be avoided, the operations must be corrected ormodified. It is well known that pruning, especially whenperformed carelessly, may lead to infection by wound parasites,but it is not generally recognised that bad planting may resultin serious disease.

An example of successional disease in Scots pine was recentlyobtained from Roxburgh in Scotland. The tree, seven yearsold, is still living, although obviously unhealthy. Some of thecurrent year's needles were green but others were brown anddead and many of the older ones had fallen. On examinationit became evident that the tree had been very badly plantedfor the main root and some of the larger laterals were bent anddirected slightly upwards. Even when planting is carefullycarried out no doubt some of the roots are killed or injured buthere the number affected must have been larger than usual.

Several young fructifications of Fomes annosus are present onthe bark just at the collar of the tree and investigation of theroots shows that a number of them are infected by the fungus,the wood being discoloured and partially rotted while thetracheids contain numerous fine colourless hyphae. Examina­tion showed that the infection had passed up into the base ofthe stem but it does not extend much above ground level.

Although there is still some doubt about the exact methodof infection by F. annosus, Hiley has shown (4, p. IIZ) that itcan attack the tree through wounded and dead roots. It isprobable that uninjured living roots cannot become infected.

Successional Disease in the Scots Pine. Malcolm Wilson 83

Planting out, even when carefully performed, probably alwaysbrings into existence the necessary predisposing factors forinfection, i.e. the presence of injured or dead roots, but carelessplanting by adding to the number of injured roots considerablyincreases the chances of infection. It has been observed thata tree which becomes infected by F. annosus shortly afterplanting out frequently shows signs of careless planting whendug up. At the present time, when the disease caused by thisfungus is becoming increasingly prevalent, it is particularlyimportant that planting should be carried out carefully byskilled workmen. The specimen is also attacked by the beetlePityogenes bidentatus*. An account of the genus Pityogenes hasbeen given by Fraser (2) who describes the occurrence of P.bidentatus in a number of places in Scotland amongst whichRoxburgh is not included. The beetle normally occurs on Pinussylvestris but Fraser states that he has never found it on youngliving trees. Munro (7) states that "at times P. bidentatus isharmful in young plantations. The beetles attack the lessvigorous plants or young trees in the region of the branchwhorls and are able to work in comparatively green andresinous material." This agrees with the present specimenwhere the galleries extend up the stem to the level of the branchwhorls.

There is a general opinion that bark beetles are secondarypests and Hartig (3, p. 17) has pointed out that they oftenattack plants injured by parasitic fungi. The rather scantyliterature on this question has recently been discussed byMunro (7) who quotes the description given by Dufrenoym of anattack of Armillaria mellea on maritime pines which wasconstantly followed by bark beetle attack.

Bark beetles are known to attack trees in which the watercontent has been diminished. This may be brought about bysevere root pruning and late planting, as shown by Munro (7)

in an attack on elm by Scolytus destructor. The same author(p. 23) also refers to an instance where "Pityogenes beetles ...attacked some rather large-sized and recently planted Corsicanpine which were already weakened by a spell of droughtfollowing the planting."

In the present specimen it may be concluded that the attackof P. bidentatus has been rendered possible by the low watercontent of the plant brought about by bad planting and attackby F. annosus, as both these latter factors result in death ofsome of the roots and consequent lowered absorption ofwater.

* I wish to express my thanks to Dr R. Stewart MacDougall to whom I amindebted for the identification of this beetle.

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84 Transactions British Myc ological Society

The specimen has also been attacked by the fungus Cerato­stomella Pini Munch", which was previously included in C.pili/era, the name given to th e group of species which causeth e " blueing" of coniferous timber. The blue coloration isevident in th e wood when transverse cuts are made in the upperpart of the stem. C. Pini has been recorded in Britain byMacallum (5) but its life history has not been fully worked outin thi s country . Munch (6) has given a very full account of thespecies of Ceratostomella which cause " blueing " in Germany andhas investigat ed not only their morphological characters butalso the physiological conditions und er which infection of thewood occurs. Growth of the mycelium takes place only in woodwhich contains a certain amount of air; it will not go on inwood saturat ed with water but, if the amount of water presentis diminished, the air content is correspondingly increased anda point is soon reached at which infection will take place.C. Pini is often found in the wood of t rees which have onlyrecently died and are still standing but apparent ly has not beenfound in the wood of living trees under natural conditions.Munch has suggested that the fungus does not grow as aparasite because th e living tissues, owing to their high wat ercontent, do not contain sufficient oxygen to render the growthof the mycelium possible. He experimented with living treesand found that when the water content of the wood was diminishedby chopping through some of the roots, successful infectionscould be performed and "blueing" result ed in the older sap­wood. In another specimen the bark and sapwood were sawnthrough half way round the stem at two levels, one abouteighteen inches above the other, so th at the wood between thetwo cuts was completely isolated from its water supply and inthis, as a result of infection, the mycelium spread in th e wholeof th e wood between the cuts.

In the specimen the hyphae of C. Pini are present in the woodof the main stem about half way up the tree, and it is suggest edthat the parasit ic habit of the fungus here can be explained bythe fact th at th e normal water supply, and consequently thewater cont ent , had been diminished firstly by th e bad plantingand consequent injury and death of some roots, and secondlyby the attack of F . annosus, whereby th e ascent of sap in theinfected roots and in the lower part of the st em was hindered.

* I wish to express my t ha nks to Mr ]. S. L. Waldie who isolated this fungusand grew it in pure cultu re upon seve ra l different media. No perithecia w.er.eobtained but numerous conidia of the Cladosporium t ype, t ypi cal of C. PI nt,were produced. No conidia of t he Graphium type were obtained in an y of thenumerous cultures made and , on account of this fact , together wit h the evidentcoloration of t he wood, it may be concluded that the fungus is CeratostomellaPini M unch ,

Successional Disease in Scots Pine. Malcolm Wilson 85

I t has been suggested by several investigators that infection ofthe wood of standing trees by C. pilifera may be brought aboutby the agency of bark beetles. Von Schrenkts). in the UnitedStates, has described trees in attacks of bark-boring beetlesassociated with the production of "blued" timber. In trees ofPinus ponderosa severely attacked by the beetle Dendroctonuspimderosae, the blue coloration of the wood seemed to spreadfrom the beetle holes, and it is suggested that the latter formchannels for the passage of the hyphae into the deeper layersof the sapwood. In this country, Macallum rs), in the paperalready referred to, has noted somewhat similar cases. In thesethe sapwood of dead but still standing trees of Pinus sylvestriswas found to be badly attacked by C. Pini and C. Piceae, andin all observed instances the bark of the trees was riddled byholes made by the pine beetle Hylesinus piniperda.

Both the conidia and ascospores of the various species intowhich C. pilifera has been split are more or less mucilaginousand in one of them, Endoconidiophora caerulescens, in whichthe conidia are especially sticky, Munch (6) has suggested thatthey may be carried by insects. Von Schrenk (8), however, failedto demonstrate the presence of spores of Ceratostomella on bark­boring beetles. In the present specimen the blue coloration ofthe wood is most marked in the vicinity of the galleries of thePityogenes and it appears probable that the infection has beenbrought about by the agency of the beetle.

In this specimen we have a succession of diseases probablyinitiated by bad planting. The attack of F. annosus was renderedpossible by the presence of injured or dead roots resulting fromplanting; the decrease in the normal water content of the tissuesconsequent on injury and death of some of the roots due to badplanting and attack by F. annosus rendered possible the attackby P. bidentatus and C. Pini and the infection by the latterfungus was probably brought about by the agency of the beetle.

REFERENCES.(I) DUFRENOY, J. Observations Biologiques sur les Xylophages du Pin Mari­

time. Bull. Soc. d'Etude et de Vulgarisation Zool. Agric. Bordeaux, 1920.(2) FRASER, J. Species of Pityogenes of Interest in Scottish Woodlands.

Trans. Roy. Scot. Abor. Soc. XXXIV (1920), 101.(3) HARTIG, R. The Diseases of Trees. Eng. Trans. 1894.(4) HILEY, W. E. The Fungal Diseases of the Common Larch. 1919.(5) MACALLUM. B. D. Some Wood-staining Fungi. Trans. Brit. Mycol. Soc.

VII (1922), 231.(6) MUNCH, E. Die Blaufaule des Nadelholzes. Naturwiss. Zeitschr. Forst­

und Landwirtsch. 1907-8.(7) MUNRO, J.W. British Bark Beetles. Forestry Commission, Bull. VIII. 1926.(8) SCHRENK, H. VON. The "Blueing" and Red Rot of Western Yellow Pine.

U.S. Dept. Agric. Bur. Plant Ind. Bull. XXXVI. 1923.(9) WILTSHIRE, S. P. Studies on the Apple Canker Fungus. II. Canker Infection

of Apple Trees through Scab Wounds. Ann. App. BioI. IX (1922), 275.