Aug. 2, 1920.] Agricultural Gazette of N.S.W. 583 



^^ Bunchy Top ^^ in Bananas* 



G. P. DARNELL-SMITH, D.Sc, F.LC, F.C.S. 



The external signs of " bunchy top " are well known, but it may be advisable 

 to call attention to some internal signs. 



Healthy banana tissue, both of the corm and of the pseudo-stem, is almost 

 dead white when first cut across. It may, of course, turn to purplish c(51our 

 on the outside soon after it has been cut with a steel knife, owing to the 

 action of tannin and the formation of a sort of ink. 



The unhealthy tissue of a bunchy top corm is pink or reddish brown. In 

 bananas in the incipient stages of the disease in the lower part of the corm, 

 irregular threads, yellowish red or light brown in colour, are seen. In more 

 advanced stages of the disease these threads are darker and I'each the base of 

 the pseudo-stem, and they may run up the stem for a considerable distance. 



From these unhealthy corms, cultures of bacteria have been obtained under 

 suitable conditions, which form white, circular, moist, glistening colonies. 

 These colonies must consequently be regarded with suspicion. 



Growers are recommended, therefore, 



1. Not to plant any bulbs showing the internal symptoms referred to. 



2. To dig out and destroy completely all bunchy top plants. 



3. To keep one set of tools for dealing with bunchy top plants, and to 



use them for no other purposes. 



Colonies of bacteria somewhat similar to those from banana corms have 

 been obtained from the roots of sugarcane showing signs of bunchy top. 



The reddish sap that collects in the hollowed out rhizome of a bunchy top 

 plant has been found to have an extraordinarily rapid withering effect upon 

 young shoots placed in it. 



The presence of the reddish threads (diseased vascular bundles) is not 

 peculiar to the bunchy top disease ; they are found in other banana diseases, 

 including the Panama disease. Dr. Brandes has given a very detailed 

 account of Panama disease in PJiytoj)atJiology, vol. 9, No. 9. Several of the 

 symptoms of this disease are found upon bunchy top plants. The Cavendish 

 banana is not supposed to be susceptible tcT the disease, which is caused by a 

 fungus, Fusarium cubense. A Fusarium fungus has occasionally been found 

 upon bunchy top nlants. 



A bunchy top plant must therefore be regarded as possibly infectious, and 

 the object of the present note is to inform growers of the advisability of 

 destroying bunchy top plants completely (to dig them out and leave them on 

 the ground is of no advantage), and to keep one set of tools for dealing with 

 affected plants and to use them for no other purpose. 



