DISEASES OF CACAO 165 



is commonly a discharge, from cracks or borer holes in the 

 diseased bark, of a reddish fluid which dries to a rusty deposit. 



When the outer bark is shaved off the diseased tissue can be 

 detected by the difference of its colour from that of the healthy 

 tissue surrounding it, which further is commonly marked off by a 

 dark brown line. The colour of the affected tissue may be 

 brownish or claret-coloured. With the latter indication, which is 

 the one commonly referred to, the deep pink colour normally 

 present in some trees is liable to be confused. 



The adjacent outer layers of the wood are usually more or less 

 discoloured, and narrow dark lines may extend for a considerable 

 distance from the point of origin. 



The injury to the tree is consequent upon the killing of the 

 patches of bark, and its severity is determined by the size and 

 position of these. The main stem or a branch may be girdled and 

 killed outright above the situation of the lesion ; the interference 

 with the functions of the bark may cause either local defoliation 

 and death of twigs or a general sickly appearance ; or the effects 

 may remain localized in the bark and natural recovery occur. 



(3) Chupon Wilt. 



The affection on the suckers is thus described by Rorer : 

 " the chupon is generally first attacked in the soft tissue near the 

 tip. A small water-soaked area can be seen on the stem which 

 gradually becomes sunken and darker in colour and spreads up 

 and down the stem, frequently girdling the shoot and causing 

 the upper part to wilt. The same disease has been observed on 

 young shoots on the upper branches of the tree. The point 

 of attack is generally in the axil of a leaf, though the leaf blade 

 or petiole may be the first part affected, the disease afterwards 

 running down into the stem." 



The Fungus. 



The causative fungus is Phytophthora Faheri, Maublanc (1909) . 



According to the original description the conidiophores are 150-200 

 microns in length, non-septate, hyaline and terminated by an apical 

 conidium, more rarely branching and bearing two conidia ; conidia 

 (sporangia) of various forms, generally lemon-shaped, with a thin smooth 

 membrane, a little thickened at the apex, 30-80 x 25-42 microns ; oospores 

 rounded, smooth, with a thick membrane, 45 microns in diameter. Rorer 

 gives the most usual dimensions of the conidia as 30-50 X 25-27 microns, 

 the number of zoospores as 15—30, the diameter of chlamydospores as 

 30—50 microns, oospores 33-40 microns. There is no swelling of the 

 sporophores below the conidia. 



J. Rosenbaum concluded after study of the bodies classed as oospores 

 (from which antheridia are always absent) that they are properly to be 

 regarded as multinucleate vegetative bodies with the function of chlamy- 

 dospores. He found their greatest frequency of diameter to be 40 microns. 



The fructifications of the fungus as seen on the pods consist 

 of a whitish down appearing behind the margin of the brown 



