Genetic Characterization and Mapping of Wheat Powdery Mildew Resistance Genes from Different Wheat Germplasm Sources
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2008-12-04
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Abstract
Powdery mildew caused by Blumeria graminis f. sp. tritici is a major economic disease in wheat (Triticum aestivum) in cool and humid, or maritime environments. Grain yield loss can reach 48% in susceptible cultivars under sever epidemics. Race-specific host resistance was identified as the most effective, consistent, and economic method of powdery mildew control. However, because of the constant virulence shifts and recombination among powdery mildew isolates, most race-specific resistance genes are ephemeral and are overcome a few years after wide deployment. Incorporation of new and novel resistance genes is imperative to maintain effective control in new wheat cultivars. The wheat germplasm lines NC96BGTD1, NC97BGTAB10, NC06BGTAG12, and NC06BGTAG13 exhibit different virulence spectrums and a high level of powdery mildew resistance in the southeastern United States. The objectives of this study were to characterize the inheritance of the powdery mildew resistance and identify simple sequence repeat (SSR) markers linked to the resistance genes in each line. The NC96BGTD1 and NC97BGTAB10 lines were crossed the cultivar Saluda and F2:3 families were developed for field and greenhouse evaluations. The NC06BGTAG12 and NC06BGTAG13 lines were crossed to the susceptible cultivar Jagger and F2:3 families were developed for greenhouse evaluation. SSR markers were used to development linkage maps to localize the genes to their respective chromosomes in each population. Phenotypic segregation among the F2:3 families indicated monogenic control of the resistance gene in each of the four populations.
The resistance in NC96BGTD1 was located to the short arm of chromosome 7D, flanked by the SSR markers Xwmc635 and Xcfd41 at a genetic distance of 5.3 cM distal and 20 cM proximal respectively. Because seed was not made available in a timely fashion, we were unable to determine if the resistance gene in NC96BGTD1 was a novel resistance gene or an allele of the Pm19 locus which is also located on chromosome 7. The gene in NC96BGTD1 was given the temporary designation MlNCD1.
The resistance gene in NC97BGTAB10 was located to the terminal tip of chromosome 2BL with the SSR marker Xwmc445 mapping 7 cM proximal to the gene. Again, because seed was not made available in a timely manner we were unable to determine the relationship between the gene in NC97BGTAB10 and the powdery mildew gene MlZec1 also located on chromosome 2BL. The gene in NC97BGTAB10 it was given the temporary designation MlAB10
The resistance genes in NC06BGTAG12 and NC06BGTAG13 mapped to the same region of chromosome 7AL and an allelism test indicated that the genes were likely alleles of each other. Furthermore, the genes mapped to the same region where the Pm1 locus resides, but detached leaf test suggested that the genes were different from each other as well as all five of the alleles at the Pm1 locus. Linkage mapping showed the resistance genes were flanked by the SSR markers Xwmc273 and Xwmc346 by a distance of 7.2 cM distal and 2.4 cM proximal in NC06BGTAG12 respectively, and 8.3 cM distal and 6.6 cM proximal in NC06BGTAG13 respectively. We were unable to determine the linkage or allelic relationship of the resistance genes in NC06BGTAG12 and NC06BGTAG13 with the Pm1 locus at this time. Thus these genes in NC06BGTAG12 and NC06BGTAG13 were give the temporary designation MlAG12 and MlAG13 respectively.
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wheat powdery mildew, Pm genes
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Degree
PhD
Discipline
Crop Science
