FURTHER CHARACTERIZATION OF THE POWDERY MILDEW RESISTANT GENE Ml5323 DERIVED FROM THE WILD TETRAPLOID WHEAT SSP. DICOCCUM

The accession MG5323 of T. turgidun ssp. dicoccum, resistant to powdery mildew, was crossed to the susceptible durum wheat cultivar Latino and a set of 122 Recombinant Inbred Lines (RILs) was produced. Genetic analysis of F1 and F2 progenies and RIL population, tested with a powdery mildew isolate O2 in controlled greenhouse conditions, indicated that a single dominant gene, temporarily designed Ml5323, controls the powdery mildew resistance at the seedling stage. Molecular markers and bulk segregant analysis were used to characterize and map the powdery mildew resistance gene. Twelve microsatellite markers were found to be linked to the resistance gene and, among them, two gSSRs (Xwmc25, Xwmc243) and one EST-SSR (CA695634), were found to be tightly linked to the resistance gene. By means of Chinese Spring nullisomic-tetrasomic and ditelosomics lines the polymorphic markers and the resistance gene were assigned to chromosome arm 2BS and were physically mapped on bin 2BS3-0.84-1.00 by Chinese Spring deletion lines. The physical mapping of the microsatellite markers linked to the Ml5323 gene confirmed the presence of this locus in the short arm of 2B on bin 2BS3-0.84-1.00 where was also located the Pm26 gene. A test of allelism between Ml5323and Pm26 was carried out in order to estabilish the relationship between these two genes located in the same bin on chromosome 2BS. The mildew resistant accessions TTD140 of ssp. dicoccoides, that carries the recessive gene Pm26 and MG5323 of ssp. dicoccum with the dominant gene Ml5323 were crossed to obtain the F1 progeny (TTD140 x MG5323). Seedlings of TTD140, MG5323 and ten F1(TTD140 x MG5323) were highly resistant to the isolate O2. Two hundred and twelve F2 families from the TTD140 x MG5323 population were evaluated for their powdery mildew reaction under greenhouse conditions following the same procedures used for the Latino x MG5323 cross. The F2 population segregated for resistance and susceptibility to isolate O2 of powdery mildew and showed a significant deviation from the theoretical 15 resistant : 1 susceptible ratio expected for two dominant genes segregating independently. The results obtained indicated that the two genes Pm26 and Ml5323 are different and linked on the bin 2BS3-0.84-1.00.