DISEASES OF BANANA 245 



from others which operate in a similar manner. They occur in 

 a very similar way, for example, in the nematode disease later 

 described. 



The internal sjnnptoms are more specific. A section near the 

 base of the pseudo-stem of a diseased plant shows the cut surface, 

 which in healthy plants is a uniform white, with rows of yellow, 

 orange, red, or red-brown spots marking the position of the 

 diseased vascular bundles. The discoloration thus revealed can 

 be traced into the rootstock, where it is exhibited very plainly, 

 especially towards the centre. It may often be followed further 

 into the central strand of the roots. In advanced cases the 

 rootstock is frequently rotted and may be putrid. The occurrence 

 of a central rot associated with the massed vascular bundles in 

 that region is of value in distinguishing Panama disease from 

 diseases in which the rot extends from the periphery. There 

 may however, even in Panama disease, be no development 

 beyond a diffused yellowing and softening of the upper part of 

 the bulb. 



Influence of External Conditions. 



The disease is destructive on all types of land, though there 

 are indications that physical differences may to some extent 

 influence the existence of the fungus in the soil. Favourable 

 conditions for the plants, as produced by rich soil, good cultiva- 

 tion and manuring, are stated to produce a greater capacity for 

 disease endurance, but there is no evidence of increased resistance 

 being obtained in this way. It would appear from the general 

 evidence that the destructiveness of the disease is mainly governed 

 in extent by the accumulation of the fungus in the planting 

 material and in the soil, so that when the disease once appears 

 in a cultivation it is only a matter of time for it to render the 

 growing of susceptible varieties impossible. The time required 

 depends on the natural factors influencing infection and on the 

 sanitary precautions taken. Wet weather has considerable 

 influence in the rapid dissemination of the disease, and it has 

 been frequently observed that extension is particularly liable to 

 occur in the direction of the flow of drainage water. In arid 

 regions or situations where banana fields are watered by irrigation 

 the disease is unknown. 



Inherent Resistance. 



The Gros Michel as stated is highly susceptible. The red or 

 claret banana is somewhat more resistant, but does not maintain 

 itself for more than a few years on infected ground. The 

 " Chinese" {Musa cavendishii) and " Congo " bananas are highly 

 resistant, the former at least, it would appear, to an extent 

 approaching immunity. The plantain [M Varadisaica) is believed 

 to be quite immune. 



