8 



LEAF EOT OR THREAD BLIGHT (Pellicularia koleroga)} 



This is quite common in all plantations except those at higher alti- 

 tudes. Of all the coffee diseases it is perhaps the most conspicuous, 

 its presence being usually indicated by the blackened leaves which, 

 after having been attacked by the fungus, are held suspended for 

 some time by its threads (PL I). It has been reported from various 

 places in India and the East Indies and recently from Surinam, and 

 no doubt is found throughout the coffee-growing regions of the West 

 Indies. A disease similar in character has also been reported from 

 Venezuela, where it is known as " candelillo " ; the real leaf rot which 

 has been reported from that country is also known by that name. 



On examination, the threads of the fungus which cause the disease 

 will be found on the lower side of the twigs where at each pair of 

 leaves it branches to form a thin web covering their undersurfaces. 

 On the newly attacked leaves this web is white, but later it becomes 

 brown. The leaves on which the fungus has obtained a better foot- 

 hold and which have turned black often have a finely mottled ap- 

 pearance, due to the thickening of the web at the points where it is 

 attached to the leaf. A fvirther stage is represented by the develop- 

 ment of the web into a parchment-like membrane completely con- 

 cealing the lower side of the leaf. This may be removed with a 

 needle or knife point " like a piece of gold beater's skin." The webs 

 correspond to the feeding form of the fungus, serving to absorb food 

 material from the leaves ; the threads to the " traveling " form, by 

 the extension of which along the stems and branches in the course of* 

 growth it reaches fresh material on which to feed. The threads 

 which are at first white become brown after a time, break and fall 

 away, but fragments often remain, sometimes concealed by the bark, 

 which serve as new sources of infection. When examined micro- 

 scopically^ the dense places are seen to be made up of flattened, much 

 branched threads, which besides acting as holdfasts may also serve 

 to draw food material from the leaf, although the thread's which 

 penetrate the leaf soon after it is attacked are probably more impor- 

 tant in food absorption. No spores or reproductive bodies have been 

 found in the Porto Eican fungus. The vegetative hyphae of the 

 webs are much branched and interlaced, the branching being often 

 at right angles. (PL VII, C.) 



The fungus avoids the sunlight, never growing on those parts of the 

 tree which are exposed to the direct rays. Possibly this habit enables 

 it to live on and injure trees from which the shade has been removed. 

 It must have a moist atmosphere for active growth. During the 

 drier months it remains quiescent, the affected leaves drop off, and the 

 plantation may appear quite free from the disease, but enough of the 



1 See also U. S. Dept. Agr., Jour. Agr. Research, 2 (1914), No. 3, p. 231. 



