Development and Characterization of Triticum aestivum-Aegilops longissima 6S(l) Recombinants Harboring a Novel Powdery Mildew Resistance Gene Pm6Sl

Powdery mildew of wheat is a foliar disease that is spread worldwide. Cultivation of resistant varieties is the most effective, economical, and environmentally friendly strategy to curb this disease. Powdery mildew resistance genes (Pm) are the primary resources for resistance breeding, and new Pm genes are in constant demand. Previously, we identified Aegilops longissima chromosome 6S(l)#3 as a carrier of powdery mildew resistance and designated the resistance gene as Pm6Sl. Here, we reported the design of 24 markers specific to 6S(l)#3 on the basis of the full-length cDNA sequences of 6S(l)#3 donor Ae. longissma accession TA1910, and the development of wheat-Ae. longissima 6S(l)#3 introgression stocks by ph1b-induced homoeologous recombination. Further, 6S(l)#3 introgression lines were identified and characterized by integration analysis of powdery mildew responses, in situ hybridization, and molecular markers and Pm6Sl was mapped to a distal interval of 42.80 Mb between markers Ael58410 and Ael57699 in the long arm of 6S(l)#3. Two resistant recombinants, R43 (T6BS.6BL-6S(l)#3L) and T27 (Ti6AS.6AL-6S(l)#3L-6AL), contained segments harboring Pm6Sl with less than 8% of 6S(l)#3 genomic length, and two markers were diagnostic for Pm6Sl. This study broadened powdery mildew resistance gene resources for wheat improvement and provided a fundamental basis for fine mapping and cloning of Pm6Sl to further understand its molecular mechanism of disease resistance.