Abstract
Phytophthora capsici Leonian causes significant yield losses in commercial squash (Cucurbita pepo) production worldwide. The deployment of resistant cultivars can complement integrated management practices for P. capsici, but resistant cultivars are currently unavailable for growers. Moderate resistance to Phytophthora crown rot in a selection of accession PI 181761 (C. pepo) (designated line #181761-36P) is controlled by three dominant genes (R4, R5 and R6). Introgression of these loci into elite germplasm through marker-assisted selection (MAS) can accelerate the release of new C. pepo cultivars resistant to crown rot, but these tools are currently unavailable. Here we describe the identification of a quantitative trait locus (QTL), molecular markers and candidate genes associated with crown rot resistance in #181761-36P. Five hundred and twenty-three SNP markers were genotyped in an F2 (n = 83) population derived from a cross between #181761-36P (R) and Table Queen (S) using targeted genotyping by sequencing. A linkage map (2068.96 cM) consisting of twenty-one linkage groups and an average density of 8.1 markers/cM was developed for the F2 population. The F2:3 families were phenotyped in the greenhouse with a virulent strain of P. capsica, using the spore-spray method. A single QTL (QtlPC-C13) was consistently detected on LG 13 (chromosome 13) across three experiments and explained 17.92–21.47% of phenotypic variation observed in the population. Nine candidate disease resistance gene homologs were found within the confidence interval of QtlPC-C13. Single nucleotide polymorphism (SNP) markers within these genes were converted into Kompetitive Allele Specific PCR (KASP) assays and tested for association with resistance in the F2 population. One SNP marker (C002686) was significantly associated with resistance to crown rot in the F2 population (p < 0.05). This marker is a potential target for MAS for crown rot resistance in C. pepo.
Highlights
Phytophthora capsici is a soil-borne oomycete pathogen with a wide host range, including all economically important species of Cucurbita (C. pepo L., C. moschata Duchesne, and C. maxima Duchesne) [1]
The mean Area Under Disease Progress Curve (AUDPC) values for the F2:3 families across the three experiments ranged from T21h.e18mteoan40A.6U9 DanPdC dviaslpuleasyefodr athseligFh2:3tlfyamleiflti-esskeawcreodssntohremthalredeisetxripbeurtimionen(tPseraarnsgoend cforeofmfic2ie1n.1t8otfosk4e0w.69neasnsd=d−is0p.l7a5y6e3d).leTfrta‐snksegwreesdsinvoersmegarledgiastiroibnuwtiaosno(Pbseearrvsoedn icno‐ oenfeficdiiernetctoifosnk, ewwitnhessom= −e0F.725:36f3a)m(Filiigeusrseh2o)w
A major quantitative trait locus (QTL) (QtlPC-C13) associated with resistance to Phytophthora crown rot in #181761-36P was mapped on chromosome 13 of the C. pepo genome
Summary
Phytophthora capsici is a soil-borne oomycete pathogen with a wide host range, including all economically important species of Cucurbita (C. pepo L., C. moschata Duchesne, and C. maxima Duchesne) [1]. It is responsible for foliar blight, fruit rot, root rot and crown rot disease syndromes in squash, and is most severe in the commercial production of C. pepo [2]. Commercial cultivars of C. pepo can be categorized into eight edible cultivar-groups belonging to either subspecies pepo (Zucchini, Pumpkin, Vegetable Marrow, Cocozelle) or subspecies ovifera (Straightneck, Acorn, Crookneck, Scallop) [11,12] These cultivar groups exhibit considerable phenotypic differences, both in horticultural traits and susceptibility to Phytophthora crown rot. The genomic loci, molecular markers and candidate genes associated with Phytophthora crown rot resistance in #181761-36P are currently unknown
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