Tsomin Yang

Molecular identification of a new powdery mildew resistance gene Pm41 on chromosome 3BL derived from wild emmer (Triticum turgidum var. dicoccoides).

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important wheat disease in China and other parts of the world. Wild emmer (Triticum turgidum var. dicoccoides) is the immediate progenitor of cultivated tetraploid and hexaploid wheats and thus an important resource for wheat improvement. Wild emmer accession IW2 collected from Mount Hermon, Israel, is highly resistant to powdery mildew at the seedling and adult plant stages. Genetic analysis using an F2 segregating population and F2:3 families, derived from a cross between susceptible durum cultivar Langdon and wild emmer accession IW2, indicated that a single dominant gene was responsible for the resistance of IW2. Bulked segregant and molecular marker analyses detected that six polymorphic SSR, one ISBP, and three EST-STS markers on chromosome 3BL bin 0.63–1.00 were linked to the resistance gene. Allelic variations of resistance-linked EST-STS marker BE489472 revealed that the allele was present only in wild emmer but absent in common wheat. Segregation distortion was observed for the powdery mildew resistance allele and its linked SSR markers with preferential transmission of Langdon alleles over IW2 alleles. The resistance gene was introgressed into common wheat by backcrossing and marker-assisted selection. Since no designated powdery mildew resistance gene has been found on chromosome 3BL, the resistance gene derived from wild emmer accession IW2 appears to be new one and was consequently designated Pm41.

Identification and genetic mapping of a powdery mildew resistance gene in wild emmer (Triticum dicoccoides) accession IW72 from Israel

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease of wheat (Triticum aestivum) in China and worldwide, causing severe yield losses annually. Wild emmer (T. dicoccoides) accession IW72 collected from Israel is resistant to powdery mildew at the seedling and adult stages. Genetic analysis indicated that the resistance was controlled by a single dominant gene, temporarily designated MlIW72. The F2 population and F3 families derived from a hybrid between IW72 and susceptible durum wheat line Mo75 were used for molecular mapping of the resistance gene. MlIW72 was linked with SSR loci Xgwm344, Xcfa2040, Xcfa2240, Xcfa2257 and Xwmc525 on the long arm of chromosome 7A. In addition, two STS markers, MAG2185 (derived from RFLP marker PSR680) and MAG1759 (developed from EST CD452874), were mapped close to MlIW72. All these markers were physically located in the terminal bin 0.86–1.00 of 7AL. The chromosome location and genetic mapping results suggested that the powdery mildew resistance gene identified in wild emmer accession IW72 might be a new allele at the Pm1 locus or a new locus closely linked to Pm1.

A “one-marker-for-two-genes” approach for efficient molecular discrimination of Pm12 and Pm21 conferring resistance to powdery mildew in wheat

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases worldwide. Pyramiding different resistance genes into single cultivar has been proposed as one remedy to provide durable resistance. Powdery mildew resistance genes Pm12 (T6BS-6SS.6SL), transferred from Aegilops speltoides to wheat cv. Wembley, and Pm21 (T6VS.6AL), introduced from Dasypyrum villosum to wheat cv. Yangmai5, conferred broad-spectrum resistance to B. graminis f. sp. tritici. Both Pm12 and Pm21 genes are located on the short arms of homologous group six involved translocated chromosomes 6SS.6BL and 6VS.6AL, respectively. Simple sequence repeat motifs of wheat simple sequence repeat (SSR) and expressed sequence tag (EST) sequences on the short arm of homologous group six chromosomes were analyzed to develop molecular markers for discriminating chromosome arms 6AS, 6BS, 6DS, 6VS, and 6SS. One EST–SSR marker, Xcau127, was polymorphic, and therefore can be used to distinguish the two resistance genes and the respective susceptible alleles. This marker allowed us to develop an efficient “one-marker-for-two-genes” procedure for identifying powdery mildew resistance genes Pm12 and Pm21 for marker-assisted selection and gene pyramiding in wheat breeding programs.