Identification and fine mapping of gummy stem blight resistance gene Gsb-7(t) in Melon.

Abstract

Gummy stem blight (GSB), caused by the Didymella bryoniae (Auersw.) Rehm, is a devastating fungal disease of melon worldwide. Breeding GSB-resistant cultivars with host resistance genes is considered to be the most economic and effective strategy to control this disease. In this study, 260 melon germplasm resources were screened for resistance to GSB, and an inbred line H55R exhibited immunity to GSB was identified. To further understand the resistance mechanism of H55R against GSB, an F2 population was obtained from a cross between the GSB-susceptible line A15 and H55R, and genetic analysis indicated that the GSB resistance in H55R was controlled by a single dominant gene, tentatively named Gsb-7(t). The Gsb-7(t) gene was finally delimited to a 140 kb interval on chromosome 7 using bulked-segregant analysis and chromosome walking strategies. Ten putative genes were annotated in this region that contains a wall-associated receptor kinase (WAK) gene MELO3C010403. The MELO3C010403 gene contains two alternative transcripts, MELO3C010403-T1 and MELO3C010403-T2, with five and seven non-synonymous mutation sites, respectively. Gene expression analysis showed that expression of MELO3C010403-T2 but not the MELO3C010403-T1 was significantly induced by the D. bryoniae at 24 hours post-inoculation (hpi), indicating that the MELO3C010403-T2 transcript of MELO3C010403 was the most likely candidate gene of Gsb-7(t). Our results offer new genetic resources and will be helpful for the development of GSB-resistant melon cultivars in the future.