Abstract
Cucurbita pepo contains two cultivated subspecies, each of which encompasses four fruit-shape morphotypes (cultivar groups). The Pumpkin, Vegetable Marrow, Cocozelle, and Zucchini Groups are of subsp. pepo and the Acorn, Crookneck, Scallop, and Straightneck Groups are of subsp. ovifera. Recently, a de novo assembly of the C. pepo subsp. pepo Zucchini genome was published, providing insights into its evolution. To expand our knowledge of evolutionary processes within C. pepo and to identify variants associated with particular morphotypes, we performed whole-genome resequencing of seven of these eight C. pepo morphotypes. We report for the first time whole-genome resequencing of the four subsp. pepo (Pumpkin, Vegetable Marrow, Cocozelle, green Zucchini, and yellow Zucchini) morphotypes and three of the subsp. ovifera (Acorn, Crookneck, and Scallop) morphotypes. A high-depth resequencing approach was followed, using the BGISEQ-500 platform that enables the identification of rare variants, with an average of 33.5X. Approximately 94.5% of the clean reads were mapped against the reference Zucchini genome. In total, 3,823,977 high confidence single-nucleotide polymorphisms (SNPs) were identified. Within each accession, SNPs varied from 636,918 in green Zucchini to 2,656,513 in Crookneck, and were distributed homogeneously along the chromosomes. Clear differences between subspecies pepo and ovifera in genetic variation and linkage disequilibrium are highlighted. In fact, comparison between subspecies pepo and ovifera indicated 5710 genes (22.5%) with Fst > 0.80 and 1059 genes (4.1%) with Fst = 1.00 as potential candidate genes that were fixed during the independent evolution and domestication of the two subspecies. Linkage disequilibrium was greater in subsp. ovifera than in subsp. pepo, perhaps reflective of the earlier differentiation of morphotypes within subsp. ovifera. Some morphotype-specific genes have been localized. Our results offer new clues that may provide an improved understanding of the underlying genomic regions involved in the independent evolution and domestication of the two subspecies. Comparisons among SNPs unique to particular subspecies or morphotypes may provide candidate genes responsible for traits of high economic importance.
Highlights
The gourd family, Cucurbitaceae, includes a number of economically important vegetable crops, of which five have a worldwide distribution and importance[1]
From 84 to 107 million of clean reads were obtained per accession (Table 1)., We applied a high-depth resequencing approach that enables the identification of rare variants
Despite the reference genome was derived from a C. pepo subsp. pepo morphotype Zucchini Spanish accession, no differences in mapping percentage was found between subsp. pepo and ovifera
Summary
The gourd family, Cucurbitaceae, includes a number of economically important vegetable crops, of which five have a worldwide distribution and importance[1]. These are cucumber (Cucumis sativus L.), melon (Cucumis melo L.), watermelon Cucurbita pepo is phenotypically the most polymorphic species of the genus[4], containing eight edible-fruited groups of cultivars (Groups), known as fruit-shape morphotypes, with fruit shape being a polygenically inherited trait that changes little during fruit growth and is of utmost consumer importance[5]. Based on molecular genetic polymorphisms[4], these eight Groups are distributed into two subspecies, C. pepo subsp. Subspecies pepo contains the Cocozelle, Pumpkin, Vegetable Marrow, and Zucchini Groups, while subsp. Subspecies pepo contains the Cocozelle, Pumpkin, Vegetable Marrow, and Zucchini Groups, while subsp. ovifera contains the Acorn, Crookneck, Scallop, and Straightneck Groups[4]
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