246 DISEASES OF CROP-PLANTS 



Control. 



The most successful form of control against Fusarium diseases 

 has been found to be the adoption of resistant varieties, and it is 

 in the search for a resistant variety with the necessary commercial 

 qualities that most hope for the control of Panama disease 

 appears to lie. The breeding of such a variety by the usual means 

 is made difficult by the partial or entire sterility of the edible 

 species of banana, but in a group with such a wealth of forms 

 it seems obvious that some type of variation must be liable to 

 occur. It should be noted that the seriousness of the disease is 

 mainly in connection with production for export. Varieties 

 adequate for local use, grown in a less systematic way, generally 

 exist undamaged. 



An enormous range of materials has been tried for the dis- 

 infection of the soil, but in this, as in other soil infections, no 

 commercially applicable method has been found. 



Rigid quarantine should be maintained against infected areas, 

 and some other crop substituted on infected land. There is no 

 guarantee that even an extended rotation will free the soil from 

 the fungus. Whether it will lessen its amount sufficiently to 

 allow for paying crops to be again obtained can only be deter- 

 mined by trial. 



Marasmius Root Disease and Stem-Rot. 



A root disease of banana, accompanied to some extent by 

 rotting of the leaf-sheaths which combine to form the pseudo- 

 stem, associated with Marasmius spp., usually, it would appear, 

 with M. semiustus Berk. & Curt. {M. stenophyllus Mont.), seems 

 to occur throughout the Antilles on bananas when grown under 

 conditions which are in some respect unfavourable. It closely 

 resembles in its nature the Marasmius root disease of sugar-cane, 

 and the same species has been recorded from the latter host. 

 The disease was investigated to some extent by F. W. South, 

 to whom the following account is mainly due, in Barbados and 

 St. Lucia, and has been the subject of notes from Jamaica (S. F. 

 Ashby) and from Trinidad. 



Symptoms. 



The outer leaves dry up more rapidly than they are replaced 

 by new growth, so that the amount of green top is reduced ; 

 in extreme cases to only two or three leaves. The drying of the 

 leaves extends to the outer layers of the pseudo-stem, which 

 turn brown or grey, and adhere closely to the layers beneath, 

 so that they are difficult to strip, or are so rotted that 

 they come away piecemeal. On and between the dead 

 leaf-sheaths are layers or patches of white Marasmius myceliiun. 

 The inner living leaf-sheaths when exposed exhibit at various 



