Variability among Colletotrichum falcatum pathotypes used for screening red rot resistance in sugarcane

摘要

Variation in cultural, pathogenic and genetic characters were examined using nine major pathotypes of Colletotrichum falcatum from tropical and sub-tropical regions of India which are mainly used for screening red rot in sugarcane. Culturally they exhibited variation in mycelial growth, colour, texture, acervuli initiation, sporulation and conidial germination. Of these, acervuli initiation and sporulation had a relation with the virulence of the pathotypes. Differential interaction studies on pathogenicity with their parental cultivars revealed that the tropical pathotypes are comparatively more virulent than to the sub-tropical types although they were able to infect all the tested cultivars. In molecular analysis, sequence analysis and phylogenetic analysis of 5.8s rDNA-ITS region of 580bp clearly showed divergence of two groups among these 9 major pathotypes. Vegetative compatibility grouping (VCG) test was standardized based on successful heterokaryon formation with nitrate non-utilizing (nit) mutants. These mutants were grouped into five major groups based on their compatibility and this approach was able to distinguish C. falcatum from other species and also it recognizes different isolates of the same pathotype. Although pathogenicity, VCG and ITS studies have slight variation in grouping the pathotypes, all the results distinguished two major groups witii the incompatibility of Cf 1148 and Cf7717 which is congruent with those groups established earlier on RAPD, differentials pathogenicity and serological approach.