Genetic Characterization of Rhizoctonia Root Rot Resistance Developed Through EMS Mutation Breeding in Wheat (Triticum aestivum L.).

Rhizoctonia root rot is an important soil-borne seedling disease of wheat in the Pacific Northwest (PNW) of the USA and growing resistant varieties is the most efficient way to manage this disease.  Scarlet-Rz1, a resistant genotype that we developed through EMS mutation breeding, is the first and only source of genetic resistance to this disease identified to date in hexaploid wheat.  The objectives of this study were to: (1) generate a double haploid (DH) mapping population and; (2) identify and develop DNA markers for Rhizoctonia root rot resistance gene(s) in Scarlet-Rz1.  Two different DH populations of 100 and 104 lines, respectively, obtained from two independent F₁s from Scarlet-Rz1 (resistant) x Scarlet-S (susceptible) were developed using microspore culture.  Plants were evaluated for Rhizoctonia root rot based on numbers of lesions on infected roots counted visually using a scale of 1 to 8.  Infected roots also were analyzed for length using WinRhizo software.  Scarlet-Rz1 and Scarlet-S had average disease scores of 1.78 and 5.82, with average root lengths of 178 cm and 131 cm, respectively.  Sixty of the 1116 SSR markers tested were polymorphic between the parents. The DH populations are currently being phenotyped for disease response and genotyped with the 60 polymorphic markers.  Marker and disease data will be used for linkage map construction and resistance gene(s) mapping.  Molecular markers identified in this study will be used in marker-assisted breeding strategies to efficiently introgress Rhizoctonia root rot resistant into wheat cultivars.