Intra-population Variability in Colletotrichum sublineolum Infecting Sorghum

Twelve monoconidial isolates were derived from a single-spore culture of C. sublineolum (isolate Cs 048) obtained from a local sorghum cultivar at Kovilpatti, Andhra Pradesh, India. The 12 isolates were evaluated for colony characteristics, spore morphology and pathogenicity on 6 sorghum genotypes in the greenhouse. The isolates differed significantly in colony growth and morphology, and spore size within themselves and compared with the parental isolate. Variation in colony growth ranged from 0.1% (Cs 048-7b-1) to 66.6% (Cs 048-1-2) relative to the parental isolate. Two of the 12 isolates showed distinct sectorial mycelial growth. Pathogenicity studies showed significant differences (P< 0.001) between isolates for latent period, virulence, aggressiveness and virulence index. Isolate Cs 048-2 was most virulent infecting all 6 sorghum lines. Five other isolates were equally virulent infecting only 2 sorghum lines each. The parental isolate infected 5 sorghum lines. Cs 048-2 was the most aggressive isolate, while the parental isolate was moderately aggressive compared with the other isolates. The most virulent and aggressive isolates generally had the highest virulence index (virulence X aggressiveness X latent period). The results indicated the inherent genetic variability between monoconidial isolates of C. sublineolum