Characterization of a new powdery mildew resistance gene in Triticum turgidum ssp. dicoccum

Powdery mildew caused by the pathogen Blumeria graminis f. sp. tritici, is a destructive foliar disease in many regions of the world. The tetraploid wheat Triticum turgidum ssp. dicoccum (2n = 4x = 28, genome AABB) shows particular promises as a donor of useful genetic variation for several traits including disease resistances to introgress in cultivated wheats. The accession MG5323, resistant to powdery mildew, was crossed to the susceptible durum wheat cultivar Latino and a set of 122 recombinant inbred lines (RILs) was produced. Segregation analysis of F2 plants combined with the resistance of F1 progeny to the isolate O2, tested under controlled greenhouse conditions, indicated that resistance is controlled by a single dominant allele. Among the 122 RILs, tested under controlled greenhouse conditions with the same isolate, 67 lines were susceptible and 55 were resistant. The segregation in the RILs fitted the 1:1 segregation ratio expected for a single resistance locus (χ 2 =1.18, 0.50 > P > 0.10). Molecular markers (gSSRs, EST-SSRs and RFLP-derived STS) were used to locate and map the resistance gene. Bulked segregant analysis (BSA), indicated that chromosome arm 2BS could be involved in the control of the resistance. Twelve genomic SSR (gSSRs), three ESTderived SSR markers (EST-SSRs) and one RFLP-derived STS, polymorphic between Latino and MG5323 and located on 2BS, were tested in the set of 122 RILs. Two gSSRs and one EST-SSR, physically mapped on bin 2BS3- 0.84-1.00, were found to be tightly linked to the resistance gene. Among the molecular markers observed in the linkage map of 2BS, few gSSRs showed Mendelian segregation (1:1), whereas most markers, showed significant deviation from the expected ratio. The marker EST-SSR, closely linked to the resistance gene, has potential use in marker-assisted selection and pyramiding of genes for resistance to powdery mildew in wheat.