Selection for host-specific virulence in asexual populations of Sclerospora graminicola

Thakur, R P and Shetty, K G and King, S B (1992) Selection for host-specific virulence in asexual populations of Sclerospora graminicola. Plant Pathology, 41 (5). pp. 626-632.

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The response to host genotype-directed selection for specific virulence in S. graminicola was studied in the pearl millet (Pennisetum glaucum)-downy mildew system. In greenhouse experiments seedlings of resistant pearl millet genotypes MBH 110 and 852B were inoculated with sporangia of a field population of S. graminicola maintained on susceptible genotypes NHB 3 and 7042. Sporangia from infected seedlings of MBH 110 and 852B were used to inoculate seedlings of MBH 110 and 852B, respectively, in succeeding generations. Within 12 generations of selection on MBH 110 and 5 generations of selection on 852B, respective host-specific virulences were identified. Selection for 852B-specific virulence was much faster than that for MBH 110-specific virulence. Symptom type, and pathogenic fitness parameters such as latent period, infection index, sporangial and oospore production were measured, and composite fitness index (CFI) was calculated for each selection generation. In general, CFI and individual fitness parameters were positively correlated with selection generation. Virulences of the host-specific pathotypes artificially selected through asexual generations were comparable to the naturally selected host-specific pathotypes AB, an MBH 110-specific pathotype from Aurangabad, and MYS, an 852B-specific pathotype from Mysore, India. The host genotype × pathogen population interaction was highly significant (P ≤0.001). The results indicate that genetic variation for host genotype-specific virulence exists within field populations of the pathogen, and that selection through asexual pathogen generations can rapidly increase the quantitative virulence of the population to resistant host genotypes. It is concluded from this that resistance and virulence in the pearl millet-downy mildew system are controlled by relatively few genes.

Item Type: Article
Subjects: Mandate crops > Millets
Depositing User: Library ICRISAT
Date Deposited: 14 Sep 2011 10:22
Last Modified: 14 Sep 2011 10:22
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Acknowledgement: UNSPECIFIED
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