Development of additive resistance in wheat, Triticum aestivum L., to stripe rust, Puccinia striiformis West

Gene action of resistance to stripe rust was determined in "minor gene lines" of wheat (P.I. 178383/Itana// commercial variety).When the minor gene lines were intercrossed, a high level of resistance was maintained in the F2 and the F3 segregating progeny.Additive gene action and high heritabilities, which were demonstrated by two dialled analyses of advanced minor gene lines, indicated that this resistance could be manipulated easily in a breeding program.Ten acceptable commercial varieties of spring wheat with resistant, intermediate, and susceptible reactions to stripe rust were intercrossed.Ten winter wheats, also acceptable commercial varieties, with intermediate and susceptible reactions were intercrossed.The most resistant seedlings (10 to 20 percent) were selected in each segregating generation, transplanted and grown to maturity.Results with 43 spring wheat crosses and 38 winter wheat crosses evaluated as seedlings in controlled environmental chambers demonstrated selection for transgressive segregation.In the field, progress towards increased resistance was demonstrated with 35 winter wheat crosses.Transgressive segregation was demonstrated in later generations for nine spring wheat crosses and 31 winter wheat ' crosses which lacked resistant progeny in the F2 and F3 generations.Thus, resistance was selected from parents which had intermediate and susceptible reaction types.The selection of resistance from crosses among susceptible varieties was demonstrated.These appear to be new sources of resistance which have been overlooked or selected against in the past.Once such resistance was built up, it could be manipulated as demonstrated with the additive, minor-gene lines.On the basis of infection results with several different virulence components in the pathogen, this resistance is believed to be of a general or non-specific nature.