Mapping Powdery Mildew and Leaf Rust Resistance Introgressed From Aegilops Speltoides Into Soft Red Winter Wheat.

The two fungal diseases powdery mildew (PM), caused by Blumeria graminis (syn. Erysiphe graminis) DC. f. sp. tritici (Bgt) Em. Marchal, and leaf rust (LR), caused by Puccinia triticina, are among the most important diseases of wheat. Both diseases can cause significant yield losses, and negatively affect grain quality. Race-specific host resistance is an economical and environmentally sound method of controlling both diseases. Several sources of resistance have come from cultivated and wild relatives of wheat.

The wheat germplasm line NC09BGTS16 (NC-TS16) was found to hold resistance to both PM and LR introgressed from Aegilops speltoides. Greenhouse and field evaluations of 144 F_2:3 families derived from a cross between NC-TS16 and the susceptible cultivar ‘Coker68-15’ indicated that a single gene conferred resistance to PM. Bulked Segregant Analysis and linkage analysis showed that the resistance gene in NC-TS16 was closely linked to SSR markers Xgwm499 and Xwmc759 on chromosome 5BL at distance 0.7cM. Additionally, the resistance gene in NC-TS16 was flanked by SNP markers IWA_6024 and IWA_2454 at distances of 0.7 and 1.4 cM, respectively. Detached leaf tests with over 80 different PM isolates were set up to differentiate the Pm gene in NC-TS16 from Pm36, which also has been located to chromosome 5BL. NC-TS16 had a different response to at least three of the isolates compared to a line containing Pm36. In addition, the NC-TS16 Pm gene and Pm36 have been introgressed from two different alien species, and it is therefore reasonable to believe that the NC-TS16 Pm gene is a novel Ae. speltoides derived PM resistance specificity.

Evaluations of the same 144 F_2:3 families for LR in the greenhouse and field indicated that at least one gene was conferring resistance to LR. Using the Bulked Segregant Analysis method, a gene conferring resistance to LR was mapped to chromosome 6BL. Differential tests and additional mapping is currently being done in order to determine whether this resistance gene is novel.