Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2009
Publication Date: 2/20/2009
Citation: Okubara, P.A., Steber, C.M., Demacon, V.L., Walter, N., Paulitz, T.C., Kidwell, K.K. EMS-treated hexaploid wheat genotype Scarlet has enhanced tolerance to the soilborne necrotrophic pathogens Rhizoctonia solani AG-8 and R. oryzae. 2009. Theor. Appl. Genet. 119(February): 293-303. Theoretical and Applied Genetics. Interpretive Summary: Rhizoctonia root rot and damping-off are two yield-limiting diseases of wheat and barley in dryland cereal production regions of the Pacific Northwest. Control measures, such as fungicides and rotation, are inadequate. No naturally-occurring genetic resistance to Rhizoctonia root rot and damping-off have been identified. Tillage is known to reduce spread of the causal agents, Rhizoctonia solani-AG-8 and R. oryzae, but the benefits of reduced (conservation) tillage, include protection against wind and soil erosion and water loss, are lost. Using mutational breeding, we have generated and characterized a unique, non-GMO hard red spring wheat genotype, Scarlet-Rz1, with genetic resistance/tolerance to Rhizoctonia solani AG-8 and R. oryzae. Tolerant plants displayed substantial root and shoot growth in the presence R. solani AG-8 and R. oryzae in greenhouse assays. The tolerance trait was transmissible in two backcross and seven selfing generations. To our knowledge, Scarlet-Rz1 represents the first Rhizoctonia-tolerant adapted wheat variety.
Technical Abstract: R. solani AG-8 and R. oryzae cause Rhizoctonia root rot and pre-emergence damping-off, yield-limiting diseases that pose a barrier to the adoption of reduced tillage wheat production systems intended to reduce soil erosion. We report the first genetic resistance to necrotrophic root pathogens Rhizoctonia solani AG-8 and R. oryzae in wheat germplasm Scarlet-Rz1. Scarlet-Rz1 was derived from the allohexaploid spring wheat (Triticum aestivum L.) cultivar Scarlet using EMS mutagenesis. Tolerant plants displayed substantial root and shoot growth in the presence 20 to 400 propagules per gram soil of R. solani AG-8 and R. oryzae in greenhouse assays. Seedling tolerance was monitored in the BC1F2, BC1F3, BC2F2, BC2F3 and BC2F4 generations of EMS-mutagenized Scarlet, and appeared to be inherited as a single co-dominant gene, named Rot1 (Rhizoctonia-tolerant1); the term “Rz1” was given to plants homozygous for Rot1. Scarlet-Rz1 was otherwise indistinguishable from wild-type Scarlet in appearance, growth habit and seed production. This novel germplasm is a promising resource for developing Rhizoctonia-tolerant wheat cultivars, as currently there are no effective control practices nor has natural genetic resistance been identified in wheat or its close relatives. Our findings also demonstrate the utility of chemical mutagenesis for generating tolerance to necrotrophic pathogens in allohexaploid wheat.