Variation in virulence and aggressiveness among pathotypes of Sclerospora graminicola on pearl millet
2002
V.P. RAO, R.P. THAKUR and
Five pathotypes of S. graminicola, specific to Pennisetum glaucum genotypes, were evaluated for virulence (a qualitative measure of the relative capacity of an isolate to infect a host genotype), aggressiveness (a quantitative measure of the infection causing potential of an isolate, calculated as disease incidence), and virulence index (a quantitative measure of virulence, measured as disease incidence Xlatent period-1) on a set of P. glaucum genotypes in a greenhouse. The pathotypes were selected from a field population of the pathogen through a number of successive asexual generations on specific host genotypes. These were named as pathotype, Path 1 (host NHB 3), Path 2 (BJ 104), Path 3 (MBH 110), Path 4 (852B) and Path 5 (a field population from a mixture of NHB 3 and 7042S). The pathotypes differed significantly in virulence, aggressiveness and virulence index on the host genotypes. Highly significant (P<0.001) pathotype X host genotype interaction effects for virulence, aggressiveness and virulence index suggested the existence of host-pathogen specificity in the P. glaucum-S. graminicola system. Differential interactions for virulence were evident on 8 of the 14 host genotypes. All 5 pathotypes were moderately virulent (3.75-7.03 virulence index) and less aggressive (28-46% incidence) on ICMP 85410 suggesting the presence of non-pathotype-specific resistance which could be more stable. It is concluded that the other P. glaucum genotypes (IP 18292, IP 18293, 7042R, P 7-4 and P 310-17), to which the pathotypes were either a virulent or less virulent, can serve as sources of stable resistance.
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