Identification and characterization of a novel powdery mildew resistance gene PmCWI45575 in wild emmer wheat

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), poses a persistent threat to global wheat production, and many widely deployed Pm genes have been overcome by new virulent races. Wild emmer wheat (Triticum turgidum var. dicoccoides) harbors abundant but underutilized resistance alleles that can broaden the genetic diversity of cultivated wheat. This study aimed to genetically dissect the powdery-mildew resistance in the wild emmer accession CWI45575.

CWI45575 exhibited strong resistance to 14 of 16 Bgt isolates at the seedling stage and complete field resistance under inoculation with a mixture of four Bgt isolates (A3, A10, E09, and E18) and naturally occurring field isolates in northern China. Genetic analysis revealed that the resistance is controlled by a single dominant gene, temporarily designated PmCWI45575. Bulked-segregant RNA-Seq (BSR-Seq) and linkage mapping delimited PmCWI45575 to a 5.3 Mb interval (716.6-721.9 Mb) on chromosome arm 4AL of the wild emmer wheat reference genome Zavitan (WEW_v2.0). This region corresponds to 718.5-724.4 Mb in the Chinese Spring reference genome (RefSeq v2.1) and does not overlap with any previously reported Pm loci on 4AL, except for QPm.tut-4A, which originates from a 7G-derived alien segment inserted into this chromosome. Transcriptome profiling identified 2,932 differentially expressed genes (DEGs) between resistant and susceptible bulks, including 96 DEGs within the mapped interval; GO and KEGG enrichment highlighted pathways related to mitogen-activated protein kinase (MAPK) signaling, hormone responses, redox regulation and phenylpropanoid biosynthesis, suggesting multilayered defense activation. A closely linked co-dominant marker, HebustP15, was developed and displayed clear polymorphism between CWI45575 and four elite but susceptible cultivars, supporting its utility for marker-assisted selection (MAS).

We identified a novel powdery mildew resistance gene, PmCWI45575, from wild emmer wheat and physically mapped it to a 5.3 Mb interval on chromosome arm 4AL. Comparison of physical location with previously reported Pm genes on 4AL suggested that PmCWI45575 is likely a novel resistance gene. BSR-Seq-based transcriptomic analysis revealed enriched defense-related pathways, providing molecular insights into the resistance mechanism. The development and validation of closely linked molecular markers offer practical tools for marker-assisted selection in wheat resistance breeding.