Abstract
Parthenocarpy is an important agronomic trait in cucumber (Cucumis sativus L.) production. However, the systematic identification of parthenocarpic germplasms from national gene banks for cucumber improvement remains an international challenge. In this study, 201 cucumber lines were investigated, including different ecotypes. The percentages of parthenocarpic fruit set (PFS) and parthenocarpic fruit expansion (PFE) were evaluated in three experiments. In natural populations, the PFS rates fit a normal distribution, while PFE rates showed a skewed distribution, suggesting that both PFS and PFE rates are typical quantitative traits. Genetic analysis showed that parthenocarpy in different ecotypes was inherited in a similar incompletely dominant manner. A total of 5324 single nucleotide polymorphisms (SNPs) associated with parthenocarpy were detected in a Genome-wide association study (GWAS) of parthenocarpy in the 31 cucumber lines, from which six parthenocarpic loci, including two novel loci (Pfs1.1 and Pfs4.1), were identified. Consequently, fifteen of the elite lines that were screened presented relatively stronger parthenocarpy ability (PFS > 90%, PFE > 50%), among which six cucumber lines (18007s, 18008s, 18022s, 18076s, 18099s, and 18127s) exhibited weak first-fruit inhibition. Three lines (18011s, 18018s, and 18019s) were screened for super ovary parthenocarpy, which showed more attractive performance. Four low-temperature-enhanced parthenocarpy lines (18018s, 18022s, 18029s, and 18012s) were identified, which were suited for breeding for counter-season production. Our approaches could help increase efficiency and lead to parthenocarpy improvements for modern cucumber cultivars.
Highlights
IntroductionThe initiation of fruit generally depends on successful pollination or fertilization
The initiation of fruit generally depends on successful pollination or fertilization.these processes are restricted by narrow environmental factors [1]
Wu et al [39] and Clavin et al [23] distinguished parthenocarpy phenotypes of cucumber into two types: initial parthenocarpic fruit and parthenocarpic fruit expansion (Figure 1). Both the percentages of parthenocarpy fruit set (PFS) and parthenocarpic fruit expansion (PFE) for 201 cucumber lines were investigated to evaluate the parthenocarpy ability of cucumber germplasm resources
Summary
The initiation of fruit generally depends on successful pollination or fertilization. These processes are restricted by narrow environmental factors [1]. As a kind of monoecious crop, a successful fruit set in cucumber depends on favorable conditions [2]. The yield of cucumber can be seriously reduced in the absence of pollinators or when planting under unsuitable environmental conditions, such as high humidity, weak light, and high temperature [3]. In 1902, Noll first introduced the term parthenocarpy in cucumbers to describe the formation of seedless fruit in the absence of functional pollination or other stimulation [4]. Breeders considered that parthenocarpy maybe provide an opportunity to overcome the problems of poor fruit setting caused by unfavorable pollinating conditions [5]. In many cucumber production areas, the main cucumber cultivars possess relatively weak parthenocarpic ability, especially in China, where the yield of cucumber is limited (FAO, 2020)
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