Submitted to: Plant Breeding
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/5/2006
Publication Date: 7/15/2006
Citation: Sun, Z., Lower, R.L., Staub, J.E. 2006. Identification and comparative analysis of quantitative trait loci (QTL) associated with parthenocarpy in processing cucumber (Cucumis sativus l.). Plant Breeding. 125:281-287. Interpretive Summary: Plant geneticists are using biotechnology even more to increase breeding efficiency and effectiveness for the release of commercial cucumber cultivars. One of these tools is the use of molecular markers (DNA-based sign posts that mark the presence of economically important traits) for DNA (the basic building blocks of life that control how plants look and perform) analysis. In cucumber this technique can be used to locate (map; put the location on a linear array such that its relationship is known with regards to other traits) genes (DNA that controls the expression of a trait) that are potentially useful for plant improvement. One such economical trait is parthenocarpy (seedless cucumber) is controlled by genes that produce more and higher quality fruit when compared to the standard commercial cultivars which produce fruits with seeds. It is important to locate the genes for parthenocarpy and place them on a map so that its location and association with other traits on the map is known. Such knowledge will allow the plant breeding to be more efficient and effective in the breeding of parthenocarpy into commercial cultivars. Therefore a study was designed to map the genes for parthenocarpy in cucumber. Between 5 to 9 genes for parthenocarpy were identified and mapped to their position on a molecular map using molecular markers. This information will be useful for increasing the efficiency and effectiveness of plant breeding whose program goal is to incorporate parthenocarpy into commercial cultivars. This will in turn lead to the earlier release of such cultivars and thus increase the competitiveness of U.S. growers in the global market place.
Technical Abstract: Parthenocarpy (seedless fruit) is an economically important yield-related trait in cucumber (Cucumis sativus L.; 2n = 2x = 14). However, the genomic locations of factors controlling parthenocarpic fruit development in this species are not known. Therefore, an F2:3 mating design was utilized to map quantitative trait loci (QTLs) for parthenocarpy using a narrow cross employing two gynoecious (F), indeterminate (De), and normal leaf (L) lines [2A (parthenocarpic) and Gy8 (non-parthenocarpic)]. Single-marker analysis, simple interval mapping, composite interval mapping, a two-QTL model, and bulk segregant analysis (BSA) were employed for QTL detection, comparison, and confirmation. QTL detection was performed employing 2A- and Gy8-coupling phase data using the parthenocarpic yield of 120 F3 families grown at two locations (E- and G-blocks) at Hancock, Wisc. in 2000. The QTL detected in this study were compared to the map locations of QTLs conditioning first-harvest yield of seeded cucumber characterized in a previous study. There were ten QTLs for parthenocarpy detected; seven operating in E-block and three in G-block. Four of seven QTL in Linkage Groups (LG) 1 and 4 and one of three QTL in LG 1 detected by QTL mapping analysis were confirmed by BSA using E-block and G-block data, respectively. Three genomic regions (two from LG1 and one from LG4) conditioning parthenocarpic QTLs (i.e., parth1.1-2A, parth1.2-2A, parth1.3-Gy8, parth1.4-Gy8, parth1.5-Gy8, and parth4.1-2A) in this study were also mapped to the same genomic regions as QTLs (nfp1.1, nfp1.4, and nfp4.2) detected for fruit yield at first-harvest as reported in the previous study. The eight fluorescence AFLP markers linked to parthenocarpy through QTL mapping defined herein are candidates for use in marker-assisted selection programs where breeding for increased levels of parthenocarpy is an objective in the elite processing cucumber populations.