206 



THE AGRICULTURAL NEWS. 



June 25, 1910. 



FUNGUS NOTES. 



THREAD AND HORSE-HAIR BLIGHTS. 



Thread blights have been known to occur on cacao in 

 the West Indies since 190-5, when they were first found in 

 Trinidad. They have been observed since, on the same host, 

 in St. Liicin, Dominica, Tobiigo and Britisli Guiana. Horse- 

 hair blight (Miiiiisiiiuis fquicriiu's) also occurs on cacao in 

 Trinidad. Earlier references to this subject will be found in 

 (he Ayrkultural A'eivs, Vols. Ill, p. 281; IV, p. 117 .and 

 VII, p. 237; also in the West Indian Bulletin, Vols. VI, 

 p. 87, and IX, p. 179. 



EXTERNAL SYMPTOMS. — An outbreak of the thread blight 

 disease has been reported recently as occurring on nutmegs 

 in Grenada. The description of the disease, as given by 

 Mr. G. G. Auehinleck, B.Sc, Superintendent of Agriculture 

 in Grenada, is as follows: — 



Running up, and closely adherent to, the shoots, could 

 be seen a thin filament made up of interwoven hyphae, the 

 filament being generally dark-brown or black, from the 

 presence of a cementing substance. A branch of the filament 

 is given off at every petiole, and, on reaching the leaf blade, 

 ramifies on its undersurface into a netwoi'k of closely 

 adpressed silky web. The finer branches of the filament are 

 almost invariably white. None of the specimens e.>iamined 

 showed fructifications. 



The thread blight was somewhat difficult to discover, 

 owing to the thickness of foliage, but once the symptoms 

 were discovered, it w^as found that practically every tree 

 examined was attacked in a greater or less degree. Infected 

 leaves were dry and papery, but seldom fell, and as a rule 

 could only be detached by a sharp jerk. No cases of large 

 branches having died back were noted, the disease at present 

 being confined to suiall twigs and leaves. Numerous cases 

 were seen of an infected leaf coming in contact with a twig 

 or leaf of a neighbouring tree, adhering thereto, and finally 

 becoming closely attached by the growing mycelium; this 

 affords an index as to the rapidity with which the disease 

 might spread, wind or birds acting as distributing agents. 



It need only be added that, on the younger twigs and 

 leaves, the threads are distinctly light-coloured, almost white: 

 while on the harder parts, where they are older, they are very 

 dark. On some lea\'es, soft pads of mycelium may he formed. 

 These, when young, are of a white, woolly appearance; when 

 older they become covered with some waxy secretion, as do 

 the threads, and form small, dark, somewhat waxy lumps here 

 and there on the leaf surface, usually on an angle between 

 two branches of the thread, which is also dark and waxy in 

 appearance. 



MicEoscoi'ic (jHARACTEKs — The threads are composed of 

 long, thick-walled, intertwined hyphae, rarely septate, and 

 not anastomosing, showing very little branching. These 

 hyphae become even thicker-walled when old, and their walls 

 are brown in colour. There are also, in the threads and in 

 the leave.s, much finer-walled hyphae, quite hyaline and 

 colourless, with numerous .septa, freely branching and exhibit- 

 ing the clamp connexions said to be characteristic of the 

 Basidiomycetes. The two forms appear to belong to the 

 same fungus. The hyphae can penetrate the leaves, and 

 possibly the buds; they are unable to pierce the bark of woody 

 tw-igs, but may [lossibly penetrate young green ones, though 

 this was not definitely observed. 



GENERAL. — A thread blight fungus, identified by Massee 



as Stilbiim nannin (Kew Bulletin, 189S, p. 112), occurs on 

 tea in India. This is supposed to be capable of spreading up 

 the plant from the ground by way of the roots, as well as of 

 attacking it from above. Both the identity of the fungus and 

 its power of spreading underground are, however, uncertain; 

 though this last point is worthy of attention, and careful 

 examination should be made of the stems of all plants 

 attacked by thread blight, to determine if the brown strands 

 can be traced back to the roots. The fungus, in India, does not 

 seem to be quite the same as that in the AVest Indies, as it 

 appears from the descriptions to remain white and to form 

 in some cases a white felt on the leaves. Horse-hair blight, 

 attributed to Mamsmius sarnientosus, also occurs on tea in 

 India, as well as on jungle plants. (See Watt and Mann, 

 Pests and Blvjhts of the Tea Plant.) 



In Ceylon, a thread blight resembling that found in 

 India occurs on tea and on nutmegs, as well as on some jungle 

 plants. It is, however, unidentified. It has been found in 

 some ca.ses, associated with horse-hair blight on tea, possibly 

 due to Marasmius sannentosus, and with the same blight on 

 nutmegs, due to Marasmius Totalis. (Fetch. Trojncal 

 Ai/riculturixf, Vols. X.WI p. 224, and XXIV, p. 2.5.) 



In Java, and the Dutch Indies generally, another form of 

 thread blight has been found on tea. This is described by 

 Bernard (Bnlletin du De2}nrtment de T Aiirieidture anx 

 Indes Neerlandaises, Nos. VI, XI and XXIII). It is white, 

 or delicate pink, easily detachable, and forms a soft pinkish 

 felt on the underside of the leaves. The pink colour on the 

 leaves is due to numerous spores formed from free basidia 

 arising from the hyphae. The fungus has been named 

 Coftirium theae, and is related to Corticiuin lilnco-fuscvni, 

 causing pink disease of cacao in the West Indies. Bernard 

 thinks Corticiuin theae is very nearly related to the fungus 

 identified as Stilhuni naituni in India; this may be so, but it 

 certainly differs in many ways from the fungus found on 

 nutmegs in Grenada. One important point is that the Java 

 fungus is unable to penetrate the host, even on the leaves. 

 A fungus, closely allied to Corticium theae, occurs on nutmegs 

 in Java, and according to Zimmermann, another species 

 of (Jorticiurr- causes thread blight of coffee in the same island. 

 Examination of specimens of thread blights in the Mycolog- 

 ical Laboratory at the Head Office of the Department would 

 appear to indicate that they may be due to different fungi in 

 different cases; it did, however, seem that the fungus on 

 nutmegs in ( irenada is the .same as one of the forms found on 

 cacao in Trinidad. 



The question of the identity of the fungi has been gone 

 into at some length for this reason. If the mycelium is in 

 general sterile, infection can only take place from the ground, 

 as is po.ssibly the case with StiUiuni »««»»i; or from pieces of 

 diseased leaves or twigs being brought by the wind or birds 

 into contact with healthy plants. But if it is due to a species 

 of Corticiuin forming spores on the leaves, another serious 

 source of infection must be taken into consideration. Fructi- 

 fications will mo.st probably be found on old diseased material, 

 and should be looked for. They may take the form 

 of toadstools, as do those of the horse-hair blights, or they 

 may appear as pink or lilac colouring on the under side of 

 diseased leaves, if the fungus is a species of Corticium. 



To summarize, there appear to be several forms of fungi 

 capable of forming thread blights, some of which belong to 

 the genus Corticium, some probably to other genera, while 

 others may be related to, or identical with, horse hair blights 

 {Jfarasniius spp.'). They are of very general distribution 

 throughout the .tropics, and occur on several host plants, 

 among which may be mentioned, tea, coffee, cacao, nutmegs, 



