Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease of wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3Sl#2 present in Chinese Spring (CS)-Aegilops longissima 3Sl#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3Sl#2 (3Sl#2S) by evaluating for Bgt-resistance of newly developed CS-Ae. longissima 3Sl#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3Sl#3 disomic addition line, was re-identified as an isochromosome 3Sl#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3Sl#3 (3Sl#3S). Based on transcriptome sequences of TA3575, ten novel chromosome 3SlS-specific markers were developed, of which, five could be used to distinguish between 3Sl#2S and 3Sl#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4), and the remaining five could identify both 3Sl#2S and 3Sl#3S. Besides, CL897, one of five markers specific to both 3Sl#2S and 3Sl#3S, could be used to detect Pm13 located at chromosome 3Sl#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3Sl#2S and 3Sl#3S, the CS-Ae. longissima 3Sl#2 translocation lines, and the 3SlS-specific markers developed in this study will provide new germplasm resources for powdery mildew resistance breeding and facilitate the transfer of Bgt-resistance genes into common wheat.

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 6Sl#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 6Sl#3 on the basis of the full-length cDNA sequences of 6Sl#3 donor Ae. longissma accession TA1910, and the development of wheat-Ae. longissima 6Sl#3 introgression stocks by ph1b-induced homoeologous recombination. Further, 6Sl#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 6Sl#3. Two resistant recombinants, R43 (T6BS.6BL-6Sl#3L) and T27 (Ti6AS.6AL-6Sl#3L-6AL), contained segments harboring Pm6Sl with less than 8% of 6Sl#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.

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Wheat powdery mildew is one of the most destructive diseases threatening global wheat production. The wild relatives of wheat comprise rich sources of diversity for powdery mildew resistance. Here, we report map-based cloning of broad-spectrum powdery mildew resistance gene Pm13 from wild wheat species Aegilops longissima. Pm13 encodes a novel mixed lineage kinase domain-like (MLKL) protein which contains an N-terminal HeLo domain and a C-terminal authentic serine/threonine kinase (STK) domain, a unique domain architecture that has not been reported in plant disease-resistance genes. The resistance function of Pm13 was validated by loss-of-function mutants, gene silencing, transgenic assay, and allelic association analyses. Thus, Pm13 represents a special class of plant resistance genes revealing a novel aspect of host-pathogen interactions. Though introgressed into wheat ~30 years ago it was hardly exploited due to linkage drag. The new lines with small Ae. longissima Pm13 segment will lead to wide-scale deployment in wheat cultivars.