Novel Wheat Powdery Mildew Resistance Genes on Chromosome 7AL.

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important fungal disease of wheat (Triticum aestivum L.) in maritime environments.  Germplasm lines NC06BGTAG12 and NC06BGTAG13 were characterized for their resistance to powdery mildew.  Segregating F2:3 populations from the crosses NC06BGTAG12 x ‘Jagger’ and NC06BGTAG13 x ‘Jagger’ were screened in the greenhouse with the powdery mildew isolate ‘Yuma’.  The NC06BGTAG12 and NC06BGTAG13 populations segregated 23 resistant: 79 segregating: 34 susceptible and 32 resistance: 73 segregating: 23 susceptible, respectively.  Both ratios indicate that the resistance was controlled by a single dominate gene (X2 1:2:1 P-value NC06BGTAG12 = 0.15 and P-value NC06BGTAG13 = 0.0693).  Bulk segregant analysis was conducted to identify the region of the genome that controlled the resistance in both germplasm lines.  SSR markers xwmc346 and xwmc809 flanked the powdery mildew resistance gene in NC06BGTAG12 at a genetic distance of 7.1 cM and 11.8 cM respectively.  SSR markers xwmc525 and xwmc273 were flanked the powdery mildew resistance gene in NC06BGTAG13 at a genetic distance of 2.1 cM and 7.5 cM respectively.  SSR markers were confirmed to be located on the long arm of wheat chromosome 7A in the deletion bin 0.90 to 1.00.  Allelism test were conducted using 224 F2:3 families from a cross between NC06BGTAG12 and NC06BGTAG13.  One family was identified as segregating, which indicated that the germplasm lines possess two independent genes that are in tight linkage with each other at a genetic distance less than one cM.  The powdery mildew allelic series of Pm 1 has been mapped the same region.  Detached leaf test with specific isolated suggest that the two genes in the germplasm lines are different than all the alleles at the Pm1 locus.  Considered in its entirety these data suggest that the genes in NC06BGTAG12 and NC06BGTAG13 are novel powdery mildew resistance genes.