Fine mapping of a novel QTL DM9.1 conferring downy mildew resistance in melon

Abstract

Downy mildew (DM) is a major foliar disease globally causing great economic loss in melon production. Utilizing disease-resistant cultivars is the most efficient approach for disease control, while discovery of disease-resistant genes is crucial for the success of DM-resistant breeding. To address this problem, two F2 populations were constructed using the DM-resistant accession PI 442177 in this study, and QTLs conferring DM resistance were mapped using linkage map and QTL-seq analysis, respectively. A high-density genetic map with the length of 1096.7 cM and density of 0.7 cM was generated by using the genotyping-by-sequencing data of a F2 population. A major QTL DM9.1 with the phenotypic variance explained proportion of 24.3-37.7% was consistently detected at the early, middle, and late growth stages using the genetic map. QTL-seq analyses on the two F2 populations also validated the presence of DM9.1. Kompetitive Allele-Specific PCR (KASP) assay was further carried out to fine map DM9.1 into 1.0 Mb interval. A KASP marker co-segregating with DM9.1 was successfully developed. These results not only provided valuable information for DM-resistant gene cloning, but also offered useful markers for melon DM-resistant breeding programs.

Crop Landraces and Indigenous Varieties: A Valuable Source of Genes for Plant Breeding

“…Transcriptomic analysis by Ling et al [ 152 ] revealed 293 genes upregulated in the resistant to downy mildew (DM) cultivar PI 442177 in comparison to the susceptible landrace ‘Huangtu’, while significant enrichment was also observed in pathways associated with defense response in PI 442177. Moreover, two landraces, ‘Huangtu’ and ‘Huangdanzi’, susceptible to DM were used with PI 442177, to produce F 2 populations for linkage analysis, resulting in the identification of a major QTL, DM9.1 , for DM resistance on Chr9 [ 153 ]. Landraces from different geographic regions were used by Oumouloud et al [ 154 ] to develop functional markers that would improve MAS for the melon Fusarium wilt resistance gene ( Fom-2 ).…”

Comparative Analysis of Transcriptomics and Metabolomics Reveals Defense Mechanisms in Melon Cultivars against Pseudoperonospora cubensis Infection

“…Experiments were conducted to assess the responses of 'K10-1 and 'K10-9 to P. cubensis inoculation at both seedling and mature stages, following the artificial inoculation procedure described by Zhang et al [2]. Each experiment incorporated a minimum of 3 biological replicates, with 30 plants from each cultivar per replicate.…”

“…Each experiment incorporated a minimum of 3 biological replicates, with 30 plants from each cultivar per replicate. Once the first true leaf fully expanded, seedlings were inoculated with P. cubensis using a spray method, in accordance with Zhang et al [2]. The spore concentration for inoculation was set at 5 × 10 3 spores/mL or higher, supplemented with 0.5 ‰ Tween, while double-distilled water (ddH 2 O) served as the control.…”

“…During the mature stage, DM occurrence was recorded at 10 and 15 dpi. Disease severity was quantified on a scale ranging from 0 to 5, where 0 represented the utmost resistance and 5 denoted extreme susceptibility, as detailed by Zhang et al [2].…”

“…Its significant horticultural and economic value has made it a prominent crop globally [1]. Global melon cultivation and production surged to 28.6176 million tons and 1.0774 million hectares, marking a 4% and 7% increase over the preceding five years, respectively [2]. Notwithstanding this growth, global melon yield faces significant threats from downy mildew (DM), a formidable disease instigated by Pseudoperonospora cubensis (P. cubensis), an oomycete class member.…”