Complete resistance to powdery mildew and partial resistance to downy mildew in a Cucumis hystrix introgression line of cucumber were controlled by a co-localized locus
Key message A single recessive gene for complete resistance to powdery mildew and a major-effect QTL for partial resistance to downy mildew were co-localized in a Cucumis hystrix introgression line of cucumber.
Downy mildew (DM) and powdery mildew (PM) are two major foliar diseases in cucumber. DM resistance (DMR) and PM resistance (PMR) may share common components; however, the genetic relationship between them remains unclear. IL52, a Cucumis hystrix introgression line of cucumber which has been reported to possess DMR, was recently identified to exhibit PMR as well. In this study, a single recessive gene pm for PMR was mapped to an approximately 468-kb region on chromosome 5 with 155 recombinant inbred lines (RILs) and 193 F2 plants derived from the cross between a susceptible line ‘changchunmici’ and IL52. Interestingly, pm was co-localized with the major-effect DMR QTL dm5.2 confirmed by combining linkage analysis and BSA-seq, which was consistent with the observed linkage of DMR and PMR in IL52. Further, phenotype–genotype correlation analysis of DMR and PMR in the RILs indicated that the co-localized locus pm/dm5.2 confers complete resistance to PM and partial resistance to DM. Seven candidate genes for DMR were identified within dm5.2 by BSA-seq analysis, of which Csa5M622800.1, Csa5M622830.1 and Csa5M623490.1 were also the same candidate genes for PMR. A single nucleotide polymorphism that is present in the 3ˊ untranslated region (3′UTR) of Csa5M622830.1 co-segregated perfectly with PMR. The GATA transcriptional factor gene Csa5M622830.1 may be a likely candidate gene for DMR and PMR. This study has provided a clear evidence for the relationship between DMR and PMR in IL52 and sheds new light on the potential value of IL52 for cucumber DMR and PMR breeding program.
The authors thank Martin Kagiki Njogu (Department of Horticulture, College of Horticulture, Nanjing Agricultural University, Nanjing, China) for critical reading of the manuscript. This research was supported by National Natural Science Foundation of China (Key Program, No. 31430075), Special Fund for Agro-Scientific Research in the Public Interest (No. 201403032), National Key Research and Development Program of China (2016YFD0101705-5), National Key Research and Development Program of China (2016YFD0100204-25), National Natural Science Foundation of China (No. 31672168), Independent Innovation of Agricultural Science and Technology of Jiangsu Province (CX(17)3016), Fundamental Research Funds for the Central Universities (No. KYZ201828).
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
The experiments were performed in accordance with all relevant Chinese laws.
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