HERITABILITY OF RESISTANCE TO BACTERIAL STREAK IN WINTER-WHEAT

Bacterial streak caused by Xanthomonas campestris pv. translucens redu ces yield of wheat [Triticum aestivum (L.) em Thell] worldwide. Attemp ts to control the disease with bactericides have been unsuccessful. Re sistant cultivars offer the best protection against yield loss, but li ttle is known about the inheritance of resistance. The objectives of t his study were to estimate the heritability of resistance to bacterial streak in soft red winter wheat and to derive an effective strategy f or selecting resistant genotypes. About 60 F-2:3 and F-2:4 lines from each of three populations (Pop1, Pop2, and Pop3) were tested for resis tance to bacterial streak in three Louisiana environments with two to three replications per environment from 1991 to 1994. Variation due to genotype x environment (GxE) interaction occurred in each of the popu lations and was one-fourth to one-half the magnitude of error variance . Heritability of resistance to bacterial streak was relatively low an d ranged from 0.12 to 0.70 (average 0.31) with parent-offspring regres sion and from 0.18 to 0.40 with variance components (average 0.36). He ritability increased by 0.22, 0.29, and 0.29 for Pop1, Pop2, and Pop3, respectively, with means of two replications and two environments. No n-normal distributions in two of the three populations may have inflat ed estimates of heritability. Across populations, four lines were resi stant in all three environments and 12 lines were resistant in two of three environments. Because of GxE interaction, testing should be cond ucted with at least two replications in two environments under high di sease pressure. Such a testing program should be effective in selectin g wheat lines resistant to bacterial streak.