Virulence Structure of the Eastern U.S. Wheat Powdery Mildew Population

Abstract

Little is known about the population structure of wheat powdery mildew in the eastern United States, and the most recent report on virulence in this population involved isolates collected in 1993–94. In the present study, wheat leaves naturally infected with powdery mildew were collected from 10 locations in the southeastern United States in 2003 and 2005 and a collection of 207 isolates was derived from single ascospores. Frequencies of virulence to 16 mildew resistance (Pm) genes were determined by inoculating the isolates individually on replicated plates of detached leaves of differential wheat lines. These virulence frequencies were used to infer local effectiveness of Pm genes, estimate virulence complexity, detect significant associations between pairs of pathogen avirulence loci, and assess whether phenotypic differences between pathogen subpopulations increased with geographic distance. In both years, virulence to Pm3a, Pm3c, Pm5a, and Pm7 was present in more than 90% of sampled isolates and virulence to Pm1a, Pm16, Pm17, and Pm25 was present in fewer than 10% of isolates. In each year, 71 to 88% of all sampled isolates possessed one of a few multilocus virulence phenotypes, although there were significant differences among locations in frequencies of virulence to individual Pm genes. Several significant associations were detected between alleles for avirulence to pairs of Pm genes. Genetic (phenotypic) distance between isolate subpopulations increased significantly (R2 = 0.40, P < 0.001) with increasing geographic separation; possible explanations include different commercial deployment of Pm genes and restricted gene flow in the pathogen population.

Interspecific and intraspecific diversity in oak powdery mildews in Europe: coevolution history and adaptation to their hosts

“…In natural plant pathosystems, reciprocal adaptations between host and pathogen result in a coevolutionary process (Clarke and Akhkha 2002). Although most studies of evolution of resistance or virulence in powdery mildew pathosystems are concerned with crop plants (e.g., Parks et al 2008), a few natural pathosystems have been investigated, e.g., the groundsel powdery mildew caused by Golovinomyces fischeri (S. Blumer) U. Braun (Laine 2005(Laine , 2007Laine and Hanski 2006).…”

Molecular detection of disease resistance genes to powdery mildew (Blumeria graminis f. sp. tritici) in wheat (Triticum aestivum) cultivars

“…This resistance gene had been widely used and had been highly effective in different parts of Europe and China years ago (Liu et al, 2000). Though the growing number of virulent strains has been reported in some parts of China, the gene occurs in high frequency in so many commercial cultivars as it is easily transferred from resistant to susceptible cultivars (Parks et al, 2008;Gao et al, 2012). Recently, Ma et al (2015) reported the presence of a new gene Pm2b in the cultivar KM2939, a Chinese breeding line, which exhibits high resistance to powdery mildew at both the seedling and adult stages.…”

“…This is consistent with the finding reported by Li et al (2012) that these genes are the most widely distributed among wheat cultivars in China. Pm8 cultivars have been grown worldwide since the 1980s and due to wide use, their effectiveness has since declined (Parks et al, 2008;Tang et al, 2014;Zeng et al, 2014). Several virulent strains of powdery mildew have emerged rendering the gene ineffective.…”

Wheat Genetic Transformation as Efficient Tools to Fight against Fungal Diseases

“…Because the cleistothecia products in late summer resist to low temperatures and drought, this allows the fungus to survive in the absence of host. In the presence of high humidity, the cleistothecia releases ascospores produced by sexual reproduction, which can then cause autumnal infections [9]. It is estimated that cleistothecia is of secondary importance for the mycelium.…”