Embryo Rescue Protocol for Interspecific Hybridization in Squash

Interspecific hybridization in Cucurbita crops (squash) is desirable for widening genetic variation and for the introgression of useful alleles. Immature ...

A Contrast of Three Inoculation Techniques used to Determine the Race of Unknown <em>Fusarium oxysporum</em> f.sp. <em>niveum</em> Isolates

Fusarium wilt of watermelon (Citrullus lanatus), caused by Fusarium oxysporum f. sp. niveum (Fon), has reemerged as a major production constraint in the ...

University of Florida

UF/IFAS Tropical Research and Education Center

Phytophthora capsici Leonian, the causal agent of foliar blight, root rot, fruit rot and crown rot syndromes in squash (Cucurbita moschata), is a devastating pathogen worldwide. Resistance to Phytophthora crown rot in University of Florida breeding line #394-1-27-12 (C. moschata) is conferred by three independent dominant genes (R1R2R3). Availability of DNA markers linked to R1R2R3 genes would allow efficient breeding for Phytophthora crown rot resistance through marker-assisted selection (MAS). The goal of the current study was to identify quantitative trait loci (QTLs) associated with resistance to Phytophthora crown rot in an F population (n = 168) derived from a cross between #394-1-27-12 (R) and Butter Bush (S) using QTL-seq bulk segregant analysis. Whole-genome resequencing of the resistant (n = 20) and susceptible (n = 20) bulk segregants revealed ~900,000 single nucleotide polymorphisms distributed across C. moschata genome. Three QTLs significantly (P < 0.05) associated with resistance to Phytophthora crown rot were detected on chromosome 4 (QtlPC-C04), 11 (QtlPC-C11) and 14 (QtlPC-C14). Several markers linked to these QTLs are potential targets for MAS against Phytophthora crown rot in C. moschata. The present study reports the first QTLs associated with Phytophthora crown rot resistance in C. moschata.

QTL-seq for identification of loci associated with resistance to Phytophthora crown rot in squash.

Editorial: Artificial Polyploidy in Plants.

Zucchini Yellow Mosaic Virus (ZYMV) is an aphid-transmitted potyvirus that causes severe yield losses in squash () production worldwide. Development of resistant cultivars using traditional breeding approaches relies on rigorous and resource-intensive phenotypic assays. QTL-seq, a whole genome re-sequencing based bulked segregant analysis, is a powerful tool for mapping quantitative trait loci (QTL) in crop plants. In the current study, the QTL-seq approach was used to identify genetic loci associated with ZYMV resistance in an F population (n = 174) derived from a cross between Nigerian Local (resistant) and Butterbush (susceptible). Whole genome re-sequencing of the parents and bulks of resistant and susceptible F progeny revealed a mapping rate between 94.04% and 98.76%, and a final effective mapping depth ranging from 81.77 to 101.73 across samples. QTL-seq analysis identified four QTLs significantly ( < 0.05) associated with ZYMV resistance on chromosome 2 (), 4 (), 8 () and 20 (). Seven markers within the QTL intervals were tested for association with ZYMV resistance in the entire F population. For , one single nucleotide polymorphism (SNP) marker (KASP-6) was found to be significantly ( < 0.05) associated with ZYMV resistance, while two SNPs (KASP-1 and KASP-3) and an indel (Indel-2) marker were linked to resistance within . KASP-3 and KASP-6 are non-synonymous SNPs leading to amino acid substitutions in candidate disease resistant gene homologs on chromosomes 20 () and 8 (), respectively. Identification of QTL and SNP markers associated with ZYMV resistance will facilitate marker-assisted selection for ZYMV resistance in squash.

Genetic Loci Associated with Resistance to Zucchini Yellow Mosaic Virus in Squash.

 Leonian causes significant yield losses in commercial squash () production worldwide. The deployment of resistant cultivars can complement integrated management practices for , but resistant cultivars are currently unavailable for growers. Moderate resistance to Phytophthora crown rot in a selection of accession PI 181761 () (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  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 F ( = 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 F population. The F: families were phenotyped in the greenhouse with a virulent strain of , using the spore-spray method. A single QTL () 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 . 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 F population. One SNP marker (C002686) was significantly associated with resistance to crown rot in the F population ( < 0.05). This marker is a potential target for MAS for crown rot resistance in .

Geoffrey Meru

Horticultural Sciences Department,
Tropical Research and Education Center

University of Florida

Embryo Rescue Protocol for Interspecific Hybridization in Squash

A Contrast of Three Inoculation Techniques used to Determine the Race of Unknown Fusarium oxysporum f.sp. niveum Isolates

Geoffrey Meru

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Horticultural Sciences Department,Tropical Research and Education Center

University of Florida

Embryo Rescue Protocol for Interspecific Hybridization in Squash

A Contrast of Three Inoculation Techniques used to Determine the Race of Unknown Fusarium oxysporum f.sp. niveum Isolates

Horticultural Sciences Department,
Tropical Research and Education Center