Genetic analysis of Karnal bunt (Neovossia indica) resistance in wheat

Embryos excised from seeds of six generations (P₁, P₂, F₁, BC₁, BC₂ and F₂) of a cross WH 283 x WH 533 were cultured on modified MS medium already inoculated with secondary sporidia ofNeovossia indica. Significant variations for callusing response (CR) (54.55–75.55%) were observed among generations but the presence or absence ofN. indicia did not affect callusing response. A clear inhibition zone (IZ) was formed around each embryo showing callusing. The diameter of IZ varied significantly among generations and was maximum in the resistant genotype, WH 283 (3.60 cm). Fresh weight and dry weight of calli, initiated from embryo cultured and inoculated withN. indica, varied significantly among generations. Coefficient of infection as well as percentage of infection reflected the overdominance of susceptibility. Generation mean analysis showed that the three parameter model was adequate for diameter of IZ only. Six-parameter model showed that additive (in presence ofN. indica), additive and additive x dominance (in absence ofN. indica) effects were also significant. Complementary type of epistasis for fresh weight of calli and dominance, and dominance x dominance effects for dry weight of calli were observed in the presence ofN. indica. Magnitude of additive effects was higher for diameter of IZ in three parameter model. Therefore, selection might assist in improving this trait and thus indirectly help in attaining the resistance towardsN. indica.