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Title: MlUM15: an Aegilops neglecta-derived powdery mildew resistance gene in common wheat

Author
item WORTHINGTON, MARGARET - North Carolina State University
item LYERLY, JEANETTE - North Carolina State University
item PETERSEN, STINE - North Carolina State University
item Brown-Guedira, Gina
item Marshall, David
item Cowger, Christina
item Parks, Wesley
item MURPHY, J - North Carolina State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2014
Publication Date: 4/25/2014
Citation: Worthington, M., Lyerly, J., Petersen, S., Brown Guedira, G.L., Marshall, D.S., Cowger, C., Parks, W.R., Murphy, J.P. 2014. MlUM15: an Aegilops neglecta-derived powdery mildew resistance gene in common wheat. Crop Science. 54(4):1397-1406.

Interpretive Summary: Powdery mildew is a major fungal disease of wheat in cool and humid climates. Genes that make wheat resistant to specific races of mildew provide a reliable, economical, and environmentally benign form of disease prevention. Molecular markers can allow breeders to “pyramid” several major genes for powdery mildew resistance into a single wheat line, which should make the resistance of that line last longer. The wheat germplasm line NC09BGTUM15 (NC-UM15) has the first form of powdery mildew resistance that was crossed into wheat from the wild wheat relative called Aegilops neglecta. Greenhouse and field tests of families from a cross between NC-UM15 and the susceptible wheat line ‘Saluda’ showed that this resistance was provided by a single dominant gene. Several different kinds of molecular markers were identified on the long arm of wheat chromosome 7A that were associated with this resistance gene. A powdery mildew resistance gene with several forms, or alleles, called Pm1 had previously been identified on the same arm of chromosome 7A, along with several other mildew resistance genes that are probably also new. Tests using 21 powdery mildew isolates showed that NC-UM15 had a different disease response pattern from that of many genes previously mapped to that chromosome arm, including all alleles of Pm1. Therefore, the MlUM15 resistance gene is most likely a new source of powdery mildew resistance. However, further tests will be required to clarify the relationship between MlUM15 and other Pm genes in this complex region of chromosome 7A.

Technical Abstract: Powdery mildew, caused by Blumeria graminis DC f. sp. tritici, is a major fungal disease of wheat (Triticum aestivum L.) in cool and humid climates. Race-specific host plant resistance is a reliable, economical, and environmentally benign form of disease prevention. The identification of molecular markers tightly linked with qualitative resistance genes can facilitate marker-assisted selection and enable breeders to pyramid several major genes for powdery mildew resistance into a single cultivar, thereby increasing the durability of race-specific sources of disease resistance. The wheat germplasm line NC09BGTUM15 (NC-UM15) possesses the first form of powdery mildew resistance introgressed from Aegilops neglecta Req. ex Bertol. Greenhouse and field evaluations of F2:3 families derived from a cross between NC-UM15 and the susceptible cultivar ‘Saluda’ indicated that a single dominant gene conferred resistance to powdery mildew. Bulked segregant analysis (BSA) showed that several simple sequence repeat (SSR), sequence tag site (STS), and single nucleotide polymorphism (SNP) markers specific to chromosome arm 7AL segregated with the resistance gene. One STS, three SNP, and three SSR markers were closely linked to the MlUM15 resistance gene on chromosome 7AL. The most likely order was Xwmc525/s8057-0.7 cM-Xcfa2257-0.4 cM-resistance gene-0.8 cM-Xcfa2240-2.8 cM-Xmag2185-3.4cM-s2929-5.4 cM-s4434. The multi-allelic Pm1 locus and several other temporarily designated genes map to this region of chromosome 7AL. Detached leaf tests conducted with 21 powdery mildew isolates revealed that NC-UM15 had a different disease response pattern from genotypes carrying Pm37, five temporarily designed genes in the area, and all alleles of the Pm1 complex. The MlUM15 resistance gene is most likely a novel source of powdery mildew resistance. However, further detached leaf and allelism tests with Pm1 and temporarily designated genes will be required to elucidate the relationship between MlUM15 and other Pm loci in this complex region of 7AL.