156 RED ROT OF SUGARCANE. 



March 17tli, 1908, the experiment was repeated with 24 canes 

 sHghtly reddened at the base but apparently clean higher up. 

 Slabs were cut from above the limit of the discoloration. Of these 

 15 showed no marks even with a lens, while 9 had minute rod points. 

 The presence of CoUetotrichmn was demonstrated in 3 of the former 

 and 1 of the latter. Therefore, in an attack of the severity des- 

 cribed, nearly 17 per cent, of apparently clean slabs, taken from 

 canes slightly affected with red rot, were shown to contain the 

 fungus withhi their tissues. Under such circumstances it would 

 have been necessary to discard all canes, any part of which was 

 discoloured ; new infections were occurring right up to harvest time 

 and some would probably have escaped even such rigorous selection. 

 It would be cheaper and more satisfactory under ordinary estate 

 conditions to discard the whole crop and import healthy seed. 

 In Pusa, since the amount of seed ret^uired was small and questions 

 of cost and trouble did not arise, it was found possible to letain 

 some of the more valuable varieties and the 1908-09 crop had little 

 disease. The amount discarded was, however, very great and would 

 have been ruinous under estate conditions. 



All that can safely be stated, so far, is that planting setts from 

 obviously diseased canes leads to a considerable development of 

 disease in the resulting crop and that, provided the variety is fairly 

 free from disease to start with, sett selection keeps red rot within 

 reasonable limits, unless some untoward circumstance, such as tlie 

 epidemic of cane-fly at Pusa in 1907-08, intervenes. 



The infection of sorxi) setts. 



If there were no other method of perpctuatijig red rut than by 

 the use of diseased seed, one could, of course, stamp it out, even in 

 view of the above facts. This brings us to the consideration of the 

 parasitism of Colletotrichum falcation and of the means at its dis- 

 posal for obtaining an entry into previously healthy cane. We can 

 then more readily discuss the further measures for its control and 

 the influence of external conditions, such as the attack of cano-fly 

 at Pusa in 1907-08, on the prevalence of tlic disease. 



