Morphological and pathogenic diversity among grain sorghum isolates of Colletotrichum graminicola in India
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Authors
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V.P. RAO, R.P. THAKUR and KUSUM MATHUR*
Genetic Resources and Enhancement Program, International Crops Research Institute for the Semi-Arid Tropics
(ICRISAT), Patancheru 502 324
Keywords:
Sorghum bicolor, Colletotrichum graminicola, Pathogenic diversity, Virulence index, Pathotypes.Abstract
Thirty-three isolates of sorghum anthracnose pathogen Colletotrichum graminicoia, collected during 1990-1994 from eight states of India were evaluated for morphological and pathogenic diversity. Colony morphology and growth rate of single-spore cultures of the isolates were compared by growing them on oat-meal agar (OMA) plates and incubating at 25°C for 10 days. The isolates showed considerable variation in colony morphology and significant (P <0.05) variations in growth rate. Pathogenic diversity of the isolates was evaluated by spray-inoculating (1 x 105 conidia ml') on six differential sorghum lines in a greenhouse (25±2°C and r h >90%). The isolates significantly (P <0.001) varied in pathogenicity (latent period, virulence, and aggressiveness). "Virulence index" calculated as (virulence x aggressiveness) x latent period:' was derived to compare the pathogenic potential of the isolates. Hierarchical clustering of the isolates based on mean virulence index grouped the 33 isolates into 6 distinct clusters. Implication of these results in further virulence analysis and anthracnose management through host plant resistance is discussed.
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