Inheritance, virulence variation, and genetic heterozygosity of sexual recombination between races of Puccinia striiformis f. sp. tritici

• Sexual recombination between races were demonstrated and illustrated complicated inheritance. • Sexual recombination between races is responsible for accounting for a high level of virulence variation and the generation of new races. • Sexual recombination between races contribute to evolution of the stripe rust pathogen due to a wide range of genetic heterozygosity. New races are responsible for the breakdown of stripe rust-resistant wheat cultivars. Sexual reproduction of Puccinia striiformis f. sp. tritici , the cause of wheat strip rust, can generate new races with virulence variation. However, the role of inter-racial hybridization in generating new races and population genetic diversity has remained unknown. So, we hybridized two single-urediospore P. striiformis f. sp. tritici isolates, 4-14 and b-5, on barberry ( Berberis aggregata ) seedlings to establish single-aeciospore F 1 progenies, and selfed the F 1 progeny 1-2 to establish 85 single-aeciospore F 2 progenies. All isolates were phenotyped on 26 Yr -single gene lines as differentials, and genotyped with the 20K genotyping-by-target sequencing (GBTS) chip for P. striiformis f. sp. tritici . The results showed that 58 different virulence phenotypes (VPs, VP1-VP58) were identified, and 57 VPs were new, showing high virulence variation (98.3-100%). Overall F 2 progenies displayed different avirulence and virulence segregation ratios at 13 of 26 Yr loci tested, at which avirulence was controlled by one dominant or recessive gene, or by two genes with different gene effects. All F 2 progenies showed a high level of heterozygosity (0.07-0.64), with a great difference of genotypic distribution, presenting a rich genetic diversity from sexual recombination. Genetic variation of the F 2 progenies mostly occurred among individuals rather than among populations. A low correlation was detected between phenotype and genotype in the F 2 progenies ( R 2 =0.0257). This study provides an insight into understanding the role of sexual recombination in the origin of new races and high level of genetic diversity as well as evolution of the stripe rust.