Variability of the wheat powdery mildew pathogen Blumeria graminis f. sp. tritici in the 2003 crop season

Abstract

Wheat (Triticum aestivum) powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases attacking this crop, reducing grain yields by 10% to 62% in Brazil. The disease can be controlled by genetic resistance of the host, but the pathogen has physiological specialization, which enables it to infect wheat cultivars that have remained resistant for years. The objective of this work was to evaluate the variability of pathogenic strains of B. graminis f. sp. tritici collected in Brazil and the effectiveness of wheat resistance genes to powdery mildew in the 2003 crop season. Plants of a differential series were inoculated with each monopustular isolate. Thirty-one combinations of effective and ineffective resistance genes were identified. Only the gene Pm4a+... remained totally effective to all isolates, and gene Pm6 was highly effective (below 10% of susceptibility), whereas genes Pm3a and Pm8 were totally ineffective (susceptible to all isolates). Genes Pm3c, D1, and D2 showed low effectiveness (above 50% of susceptibility), and genes Pm1, 2, 4a, 1+?, and 2+Mld had mean effective results to most strains (susceptibility between 10% and 49%). The virulence formula Pm1, 3c, 4a, 6, 1+?, 2+Mld, 4a+..., D2 (effective genes) / 2, 3a, 8, D1 (ineffective genes) was most frequently found, accounting for 15% of the occurrences. The most frequent number of ineffective genes was seven, ranging from three to ten.

Identification of Stable Resistance to Powdery Mildew in Wheat Based on Parametric and Nonparametric Methods

“…As the Southern Cone of South America represents a geographically well separated epidemiological area for wheat powdery mildew, it is not surprising that lines with race‐specific resistance genes react differently in this environment. Virulence surveys have for instance shown that Pm4a and Pm6 , which are ineffective in most parts of Europe and China, are highly effective in Brazil (Costamilan, 2005). The median polish identified specific interactions with higher than normal susceptibility for lines 1, 2, 13, and 19 in this environment.…”

A search for 4 specific markers linked to Pm3 alleles for resistance to powdery mildew (Blumeria graminis) in rye (Secale cereale)

“…This species is an important object of research in many countries. Studies on resistance to powdery mildew in wheat have been conducted in Nordic countries (Hysing et al 2007), Slovakia (Bojnanska 2009), Czech Republic (Svec et al 2002;Vechet 2006), France (Zeller et al 1993), Lithuania (Liatukas & Ruzgas 2008, 2009), Brazil (Costamilan 2005), India (Ahmadi et al 2011), the USA (Niewoehner & Leath 1998;Parks et al 2008), Poland (Kowalczyk et al 1998), andTurkey (Spetsov et al 2013). Those studies mainly located resistance genes on chromosomes and identified molecular markers linked to those genes.…”

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

“…The gene usually exhibits its best expression from the third leaf stage of wheat growth and thereafter, it is moderately effective, but recognizable at the seedling stage (Bennett, 1984;Qin et al, 2011;Li et al, 2014). Virulence matching the Pm6 gene has occurred in many regions but still, the gene remains effective in some areas, especially when other genes such as Pm2 and Pm4b are combined during their use (Cai et al, 2005;Costamilan, 2005;Shi et al, 2009;Purnhauser et al, 2011). This could be one of the possible reasons why the two cultivars were resistant during the study (data not presented) as the genes such as Pm2, Pm4b and Pm8 were also possibly present in these cultivars.…”