igo DISEASES OF CROP-PLANTS 



an affection widespread in Ceylon in which the emergence of a 

 viscid liquid from one or more cracks leads to the formation on 

 the surface of the stem of black streaks and patches, which may 

 be small or may extend for several feet, and are found to be 

 connected with strands or cylinders of rotted interior tissue 

 which in some cases run nearly the whole length of the trunk. 

 In old and hardened trees the external patches are small and the 

 internal decayed part is usually not more than lo centimetres 

 in diameter. The disease was found to be due to infection of the 

 cortical tissue through surface cracks with the fungus Thielaviop- 

 sis paradoxa. The decay is slow and no effect on the health and 

 bearing of the tree is usually apparent. S^Tnptoms of this type 

 have not been observed by the present writer. 



A condition more nearly resembling the Trmidad affection 

 described above is also mentioned by Petch and regarded as 

 distinct, being attributed to the effects of injury by root disease 

 root asphyxiation, fire, or lightning. 



In Jamaica, according to observations made by S. F. Ashby, 

 natural cracks an inch or more long tend to form on the trunks of 

 trees when rain sets in following a dry period. Thielaviopsis 

 has been found, not infrequently, to start a brown rot at these 

 wounds which may penetrate deeply if neglected. 



Extensive yellowish or reddish sodden discoloration of the 

 outer tissues of the tnink at or near the base with exudation of 

 rusty fluid and gum also occurs, and may be followed by the 

 death of the trees. The affected tissues are soaked with gum, 

 but no definite parasite has been detected unless it be a small 

 yeast in the intercellular spaces, not always to be found, however. 

 It will be noted that the description closely resembles that of the 

 Trinidad affection. 



The treatment adopted in Trinidad consists of the paring 

 away of the discoloured tissues, an operation which, owing to the 

 confluence of numerous patches, often involves the removal of 

 large areas of the rind, and the application of a coating of crude 

 oil or distillate. This, if thoroughly carried out, has the effect 

 of arresting the progress of the rot, and in most cases the tree 

 withstands even severe cutting very well. It is obviously 

 desirable, however, that the treatment should be applied early, 

 and the site occasionally re-examined. 



Leaf-Dwindling or Little-Leaf Disease. 



This affection occurs in Grenada and Tobago and is at the 

 present time quite common in Trinidad, where it is particularly 

 conspicuous on the wayside trees seen in the neighbourhood of 

 villages. A similar affection described by S. F. Ashby under the 

 name Hard or Little Leaf-bitten Disease is reported to be widely 

 distributed in coconut cultivations in Jamaica. 



