Identification and Molecular Marker Development for Powdery Mildew Resistance Gene Pm2R in Melon (Cucumis melo)
HAN Wei-Qi1,2,*, MA Jian2,*, LU Meng-Qing1,2, YUAN Guo-Liang2, DING Zhuo1,**, CUI Hao-Nan1,**
1 College of Horticulture Science and Technology, Hebei Normal University of Science & Technology, Qinhuangdao 066600, China; 2 State Key Laboratory of Vegetable Biobreeding, Beijing Vegetable Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China
Abstract：Powdery mildew is one of the most devastating fungal diseases affecting melon (Cucumis melo) production. The identification of elite resistance sources and the elucidation of their underlying resistance genes are of great practical significance for breeding melon cultivars with improved powdery mildew resistance. This study aimed to elucidate the genetic mechanism underlying powdery mildew resistance and to identify resistance genes in the melon inbred line 19PMR exhibiting immunity to powdery mildew, thereby providing a theoretical foundation and potential gene resources for breeding powdery mildew-resistant varieties. In this study, a segregating population was constructed using 19PMR and the highly susceptible inbred line 19PMS as parents. The powdery mildew disease assay by artificial inoculation with Podosphaera xanthii was conducted for genetic analysis. The candidate gene was preliminary mapped using bulked segregant analysis sequencing (BSA-seq) strategy, and specific molecular markers were developed based on sequence polymorphisms. The results showed that the resistant parent 19PMR and the F1 plants exhibited immunity to powdery mildew, and the segregation ratio of resistant to susceptible individuals of F2 population among 292 F2 plants was 3∶1, indicating that the resistance in 19PMR was controlled by a single dominant gene, tentatively named Pm2R. Subsequently, the Pm2R gene was located within the 0~1.66 Mb interval at the distal end of the short arm of chromosome 2 using the BSA-seq method. This interval contained 2 tandem genes, MELO.jh002936 and MELO3C015354, which encoded nucleotide-binding site and leucine-rich repeat (NBS-LRR) proteins. Further sequence analysis revealed a fragment deletion in the MELO3C015354 gene region of the susceptible parent 19PMS, while multiple sequence variations in MELO.jh002936 gene were identified between the 2 parents. Based on a 10-bp sequence variation in the promoter region of MELO.jh002936, an insertion/deletion (InDel) marker ID1152 was developed, which co-segregated with the resistance phenotype in 292 F2 individuals. In summary, this study demonstrated that the powdery mildew resistance of melon 19PMR was controlled by a single dominant gene, Pm2R, located on chromosome 2 within the 0~1.66 Mb interval. Furthermore, MELO.jh002936 and MELO3C015354 were identified as potential candidate genes for powdery mildew resistance, and the molecular marker ID1152 is expected to be applicable for marker-assisted selection (MAS) breeding programs for powdery mildew resistance in melon.
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