Genetic and molecular studies of loose smut resistance in Durum Wheat
Randhawa, Harpinder Singh
The most economic and effective way to control loose smut disease of wheat is by the development of resistant cultivars. This study was conducted to screen tetraploid species of wheat resistant to Ustilago tritici races, to investigate the genetic similarities among different races of U. tritici, to determine the genetic control of resistance to race T33 in three crosses and to identify molecular markers linked to loose smut resistance. About 160 selected lines of tetraploid species of Triticum carthlicum, T. dicoccoides, T. dicoccum, T. polonicum, T. turanicum, and T. turgidum were screened for resistance to three races (T33, T32, and T26). The highest percentage of resistant lines was observed in three species, T. carthlicum, T. dicoccoides, and T. dicoccum to the three races of U. tritici. T. polonicum, T. turanicum, and T. turgidum had a lower percentage of resistant lines. Twenty races of U. tritici collected from durum and bread wheat were analysed to assess the degree of similarity based on molecular genetic data. Cluster analysis indicated that races collected from durum and bread wheat did not have any consistent grouping according to the wheat species they were collected from. Three crosses (Stewart 63 x Biodur, DT662 x D93213, and D93221 x DT658)were evaluated to determine the inheritance of resistance to race T33 of U. tritici. In Stewart 63 x Biodur, resistance appeared to be dominant and under the control of more than one gene, probably one major gene along with minor gene(s). Resistance in DT662 x D93213 was dominant and controlled by a single gene whereas in D93221 x DT658, resistance was recessive and conditioned by three genes. Although, allelic studies were not conclusive, the presence of smutted progenies from crosses among the resistant parents as well as the results of molecular studies indicate that the resistance genes studied may not be allelic. To identify molecular markers linked to loose smut resistance, bulked segregant analysis was used to screen two recombinant inbred populations from the crosses Stewart 63 x Biodur and DT662 x D93213. In the Stewart 63 x Biodur population, five Amplified Fragment Length Polymorphism (AFLP) markers were identified. Two markers were on one side of a smut resistance locus at a distance of 19.3 cM whereas three markers were on the other side at a distance of 15.5 cM. Marker E32/M55R accounted for up to 41% of the disease reaction variability. Since these markers were flanking the smut resistance locus, they can be effectively used for marker-assisted selection despite being loosely linked. In DT662 x D93213, five markers including two AFLP, two wheat microsatellites (WMS) and one Sequence Characterized Amplified Region (SCAR) were identified. The SCAR marker was on the one side of a smut resistance locus at a distance of 3.2 cM and accounted for up to 64% of the disease reaction variability whereas the other markers were on the other side of the smut resistance locus at distances ranging from 5.9 cM to 35.9 cM.