Inheritance of high levels of adult-plant resistance to stripe rust in five spring wheat genotypes

Inheritance of adult-plant resistance to stripe rust (caused by Puccinia striiformis Westend. E sp. tritici) in five spring wheats (Triticum aestivum L. em. Thell) following inoculation with the Mexican race Mex96-11 was studied. All possible crosses among these resistant genotypes and a susceptible genotype, 'Avocet-YrA', were made in a one-way diallel mating design. F-1 crosses, F-2 populations, and F-2:F-3 and F-5 single seed-descent lines were evaluated under artificial field epidemics initiated with race Mex96-11. The adult-plant resistance in crosses of resistant parent with Avocet-YrA tended to be incompletely dominant and was based on the interaction of gene Yr18 and at least three additional additive genes in each parent. Transgressive segregation was detected in all F-2 populations and F-5 single seed-descent lines of the resistant parent inter-crosses, indicating that some additive genes were nonallelic. Combining ability analyses indicated that additive gene effects were more important than nonadditive gene effects in the inheritance of adult plant resistance to stripe rust in the evaluated material. Estimates of narrow-sense heritability ranged from 0.88 to 0.96. Stripe rust resistance in these wheats is expected to be durable.