Characterization and QTL Mapping of Parthenocarpic Fruit Set in Processing Cucumber (Cucumis sativus L.).

摘要

Parthenocarpy is a desirable trait for cucumber production and is particularly valuable in environments where pollination is difficult or adversely affected by abiotic factors. Parthenocarpic cucumber cultivars have been successfully developed, but the genetic and molecular mechanisms behind parthenocarpic expression remain largely unknown. Since parthenocarpy is often considered a yield component, it is difficult to separate the true parthenocarpic character from other yield related traits. Therefore, this study was designed to better define what is considered true parthenocarpic expression and then to use this knowledge to identify QTL associated with parthenocarpic fruit set. Building off of previous studies demonstrating that parthenocarpic fruit set is initiated in the days before and immediately after anthesis, a new approach to phenotyping parthenocarpic fruit set in cucumber focused on early fruit initiation and development was implemented. With a clear approach to phenotypic evaluation, a mapping population consisting of 205 F3 families derived from a cross between processing cucumber inbred lines '2A' (parthenocarpic) and 'Gy8' (non-parthenocarpic) was evaluated for parthenocarpic fruit set. Genotypic data collected for each F2 individual was utilized to construct a linkage map consisting of 192 marker loci in seven linkage groups and covering 571.7 cM. Multiple QTL mapping methodologies (interval mapping, composite interval mapping, and multiple interval mapping) were employed to detect and construct optimal models for the inheritance of parthenocarpic fruit set. Seven additive QTL associated with parthenocarpic fruit set were detected with four identified consistently in all analyses. The four consensus QTL were located on chromosome 5 at 32.3 - 54.7 cM, chromosome 6 at 0.0 - 9.7 cM, chromosome 6 at 80.0 - 83.0 cM, and chromosome 7 at 21.8 - 32.1 cM. Bioinformatic analysis of the genomic regions harboring the four consensus QTL was conducted and multiple candidate genes were identified. A model was proposed to explain the roles of potential candidate genes in parthenocarpic expression observed in cucumber. The QTL identified for parthenocarpic fruit set by this study are valuable to cucumber breeders interested in developing parthenocarpic cultivars and to researchers interested in the genetic and molecular mechanisms of parthenocarpic fruit set.