Genotypic interaction between resistance genes in wheat and virulence genes in the Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae).

The genotypic interaction between wheat resistance genes H3, H6, H7H8, H9 and virulence genes vH3, vH6, vH7vH8, vH9 of Hessian fly, Mayetiola destructor (Say), was studied in a growth chamber. Results showed that plants homozygous and heterozygous for the H3 gene expressed a high level of resistance against homozygous avirulent and heterozygous larvae carrying the vH3 virulence allele. The H7H8 genes were highly effective in the homozygous condition, but displayed a reduced level of resistance in the heterozygous condition. The H6 and H9 genes showed different levels of resistance against the reciprocal heterozygous larvae (vH6(a)vH6(A) versus vH6(A)vH6(a) and vH9(a)vH9(A) versus vH9(A)vH9(a)). Adults reared from vH6(a)vH6(A) and vH9(a)vH9(A) larvae were all males, consistent with the vH6 and vH9 X-linkage. Plants homozygous for H3, H6, H7H8, and H9 allowed for greater larval survival of heterozygous larvae, which suggests that avirulence to these resistance genes is incompletely dominant. Greater survival of homozygous avirulent larvae on heterozygous plants (H3h3, H6h6, H7h7H8h8, H9h9) suggests incomplete dominance of these wheat genes. Survival of heterozygous along with homozygous virulent larvae would reduce selection pressure for virulence in Hessian fly populations infesting fields of resistant wheat cultivars. This would be expected to slow the increase in frequency of virulence alleles that often results from deployment of resistant cultivars.