Inheritance and Linkage of Virulence Genes in Chinese Predominant Race CYR32 of the Wheat Stripe Rust Pathogen Puccinia striiformis f. sp. tritici

Abstract

Puccinia striiformis f.sp. tritici (Pst) is the causal agent of stripe (yellow) rust on wheat. It seriously threatens wheat production worldwide. The obligate biotrophic fungus is highly capable of producing new virulent races that can overcome resistance. Studying the inheritance of Pst virulence using the classical genetic approach was not possible until the recent discovery of its sexual stage on barberry plants. In the present study, 127 progeny isolates were obtained by selfing a representative Chinese Yellow Rust (CYR) race, CYR32, on Berberis aggregate. The parental isolate and progeny isolates were characterized by testing them on 25 wheat lines with different Yr genes for resistance and 10 simple sequence repeat (SSR) markers. The 127 progeny isolates were classified into 27 virulence phenotypes (VPs), and 65 multi-locus genotypes (MLGs). All progeny isolates and the parental isolate were avirulent to Yr5, Yr8, Yr10, Yr15, Yr24, Yr26, Yr32, and YrTr1; but virulent to Yr1, Yr2, Yr3, Yr4, Yr25, Yr44, and Yr76. The VPs of the parental isolate to nine Yr genes (Yr6, Yr7, Yr9, Yr17, Yr27, Yr28, Yr43, YrA, and YrExp2) and the avirulence phenotype to YrSP were found to be heterozygous. Based on the segregation of the virulence/avirulence phenotypes, we found that the VPs to Yr7, Yr28, Yr43, and YrExp2 were controlled by a dominant gene; those to Yr6, Yr9, and YrA (Yr73, Yr74) by two dominant genes; those to Yr17 and Yr27 by one dominant and one recessive gene; and the avirulence phenotype to YrSP by two complementary dominant genes. Molecular mapping revealed the linkage of 10 virulence/avirulence genes. Comparison of the inheritance modes of the virulence/avirulence genes in this study with previous studies indicated complex interactions between virulence genes in the pathogen and resistance genes in wheat lines. The results are useful for understanding the plant-pathogen interactions and developing wheat cultivars with effective and durable resistance.

Study of Inheritance and Linkage of Virulence Genes in a Selfing Population of a Pakistani Dominant Race of Puccinia striiformis f. sp. tritici

“…By testing the parental and progeny isolates on 24 wheat Yr single-gene lines, the parental isolate was found to be homozygous for its avirulence phenotypes to Yr5, Yr10, Yr15, Yr24, Yr32, YrSp, YrTr1, YrTye, YrExp2, and Yr26; homozygous for its virulence phenotypes to Yr1, Yr2, Yr3, Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, Yr27, Yr28, YrA, Yr32, and Yr47; and heterozygous for its VPs to Yr1, Yr2, Yr9, Yr17, Yr47, YrA, YrSp, YrTr1, YrExp2, and Yr47. Heterozygosity and homozygosity of avirulence/virulence phenotypes have been reported using selfed populations of PST isolates of Chinese races [27,28], a US race of PST [41], and a Chinese predominant race CYR32 of PST [7]. We found that both Yr5 and Yr15 genes were resistant against all the progeny isolates and the parental isolate, indicating their effectiveness in China and Pakistan, which correlates with previous studies [7,27,28,41].…”

“…The segregation of avirulence/virulence phenotypes on 10 Yr single-gene lines determined that the VPs to YrSp, YrTr1, and Yr47 were controlled by a single locus; those on six Yr single-gene lines (Yr1, Yr2, Yr9, Yr17, Yr27, and YrA were controlled by two loci. Both single-locus and two loci have been reported in previous studies [7,27,28,41]. Tian et al [27] reported one locus controlling virulence phenotypes to YrSp, which is similar in this study.…”

“…Through virulence testing of the progeny isolates, Yuan et al [41] found homozygous avirulence phenotypes for Yr10, Yr24, Yr32, and YrTr1. The homozygous avirulence phenotypes to Yr10, Yr24, Yr26, Yr32, and YrTr1 have also been reported [7].…”

“…Heterozygosity and homozygosity of avirulence/virulence phenotypes have been reported using selfed populations of PST isolates of Chinese races [27,28], a US race of PST [41], and a Chinese predominant race CYR32 of PST [7]. We found that both Yr5 and Yr15 genes were resistant against all the progeny isolates and the parental isolate, indicating their effectiveness in China and Pakistan, which correlates with previous studies [7,27,28,41]. In addition to the avirulence phenotypes produced by these two genes, avirulence genes to eight other Yr single-genes (Yr10, Yr24, Yr32, YrSp, YrTr1, YrTye, YrExp2, and Yr26) were also homozygous in this study.…”

“…In China, severe stripe rust epidemics occurred in 1950, 1964, 1990, and 2002 [5,6]. In recent years, 1.65 million hectares of the wheat crop were affected by this pathogen in 12 provinces in China [7]. Although disease varies in its frequency of occurrence and impact of damage, almost every country has this problem, for example, in Australia, New Zealand, India, Nepal, China, Pakistan, Yemen, Uzbekistan, Kenya, Ethiopia, the United Kingdom, Peru, Chile, Colombia, Ecuador, Mexico, and the US, it caused 5-10% yield losses.…”