Development of KASP Markers and Identification of a QTL Underlying Powdery Mildew Resistance in Melon (Cucumis melo L.) by Bulked Segregant Analysis and RNA-Seq.

Yanyan Cao,Qiannan Diao,Hongmei Zhang,Yongping Zhang,Haijun Jin,Youyuan Chen

doi:10.3389/fpls.2020.593207

Yanyan Cao, Qiannan Diao + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2020.593207

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Abstract

Powdery mildew (PM), caused by Podosphaera xanthii (Px), is one of the most devastating fungal diseases of melon worldwide. The use of resistant cultivars is considered to be the best and most effective approach to control this disease. In this study, an F2 segregating population derived from a cross between a resistant (wm-6) and a susceptible cultivar (12D-1) of melon was used to map major powdery mildew resistance genes using bulked segregant analysis (BSA), in combination with next-generation sequencing (NGS). A novel quantitative trait locus (QTL) named qCmPMR-12 for resistance to PM on chromosome 12 was identified, which ranged from 22.0 Mb to 22.9 Mb. RNA-Seq analysis indicated that the MELO3C002434 gene encoding an ankyrin repeat-containing protein was considered to be the most likely candidate gene that was associated with resistance to PM. Moreover, 15 polymorphic SNPs around the target area were successfully converted to Kompetitive Allele-Specific PCR (KASP) markers (P < 0.0001). The novel QTL and candidate gene identified from this study provide insights into the genetic mechanism of PM resistance in melon, and the tightly linked KASP markers developed in this research can be used for marker-assisted selection (MAS) to improve powdery mildew resistance in melon breeding programs.

Highlights

Melon (Cucumis melo L.), which belongs to the Cucurbitaceae family, is an important horticultural and economic crop worldwide (Garcia-Mas et al, 2012)
This indicated that resistance to P. xanthii in wm-6 was conferred by a single recessive gene
It has been reported that the ankyrin repeat-containing (ANK) protein NPR1 is important both in the SA-dependent immune response and in SA-independent resistance responses induced by the root-associated bacteria (Cao et al, 1997; Ryals et al, 1997); AKR2 functions in the oxidative metabolism of disease resistance and stress response in Arabidopsis (Yan et al, 2002); a plasma membrane-localized ANK protein, ACD6, is involved in SAdependent signaling in defense responses and programmed cell death (Lu et al, 2003, 2005), and ectopic expression of the ANK protein OsBIANK1 of rice confers enhanced disease resistance to Botrytis cinerea and Pseudomonas syringae in Arabidopsis (Li et al, 2013)

Summary

Introduction

Melon (Cucumis melo L.), which belongs to the Cucurbitaceae family, is an important horticultural and economic crop worldwide (Garcia-Mas et al, 2012). Powdery mildew (PM) is a fungal disease that occurs commonly on leaves, petioles, and stems of most cucurbit crops in both field and greenhouse conditions (Perez-Garcia et al, 2009) This disease can result in a decrease in weight-based productivity and a reduction in fruit quality (Candido et al, 2014), thereby causing severe economic losses in many areas of the world (Romero et al, 2008). Melon PM is often caused by Podosphaera xanthii (Px) and Golovinomyces cichoracearum (Gc) (Krístková et al, 2009; Li et al, 2017) These two fungi can be distinguished by observation of the pathogens’ cleistothecia, conidia germination, microscopic morphology, and host identification (Liang et al, 2010; Liu et al, 2010). Px can coexist with the diseased plants in the soil as hyphae, conidia and cleistothecia, or it can overwinter as hyphae on greenhouse plants, and when the temperature rises the subsequent year, the conidia are distributed by air or water to infect the plants (Zhang et al, 2007)

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