GENE-EXPRESSION IN THE TRITICUM-AESTIVUM PUCCINIA-RECONDITA F SP TRITICI GENE-FOR-GENE SYSTEM

The progeny of a selfed, single-uredinial isolate of Puccinia recondita f. sp. tritici segregated for virulence on near-isogenic Thatcher wheat lines with leaf rust resistance genes Lr2a, Lr2c, Lr3, Lr3ka, Lr11, Lr17, and Lr30. Progeny isolates that produced the lowest avirulent infection types on the homozygous Thatcher lines were assumed to be homozygous for avirulence alleles; isolates that produced intermediate infection types were assumed to be heterozygous; and isolates that produced high infection types were assumed to be homozygous for virulence alleles. The seven homozygous Thatcher lines were crossed with Thatcher to produce F, plants. The F, plants were selfed, and the F-2 plants were inoculated with the three different progeny isolate genotypes, such that host lines and rust isolates were evaluated for infection type in all nine genotype combinations for each of the seven corresponding gene pairs in T. aestivum and P. r. tritici. The expression of the resistance genes ranged from complete dominance to complete recessiveness, whereas expression of the avirulence genes ranged from nearly complete dominance to complete recessiveness. The expression of resistance and avirulence genes in the wheat leaf rust gene-for-gene system was found to be highly dependent on the genotypes of the rust isolates and host lines involved in the interactions.