Screening sugarcane for red rot resistance caused by Colletotrichum falcatum went

摘要

Red rot (RR) of sugarcane is one of the main limiting factors in cane yield and quality. Sugarcane varieties exhibit variation with regard to resistance against RR. (Kalaimani and Natarajan, 1994). Due to development of new pathotypes in the RR flora, the commercial varieties like CoC 671, CoC 85061, CoC 86062, CoSi 86071, CoC 90063, CoC 91061, CoC 92061 and CoSi 98071 have become susceptible to RR (Kalaimani and Natarajan, 1994). Hence, evaluation process has to be continued without break so that resistant/moderately resistant clones are ready on the pipeline to replace susceptible ones. With this view, 80 genotypes found promising in other attributes were screened for red rot at the Sugarcane Research Station, Cuddalore during 1997-98. The entries were planted in a randomised block design with two replications along with the susceptible standards. Twenty five canes of each clone were inoculated by plug method (Srinivasan and Bhat, 1961) when the plants attained the age of seven months. A composite inoculum of C. falcatum was prepared by mixing the seven days old spore suspension of six profusely sporulating RR isolates. Inoculation was done in the middle of the third exposed internode from bottom. One mm bore holes were made with the help of IISR cane inoculator and one ml spore suspension @ 10~6 concentration was injected into the bore hole of each cane. The holes were immediately sealed with plastic clay to avoid aerial contamination. Sprinkler irrigation was provided to the crop for thirty, days to create humid condition for easy infection. After an incubation period of two months, the inoculated canes were split open longitudinally along the point of inoculation and graded as for the international scale of 0-9 as follows.