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Molecular mapping reveals structural rearrangements and quantitative trait loci underlying traits with local adaptation in semi-wild Xishuangbanna cucumber (Cucumis sativus L. var. xishuangbannanesis Qi et Yuan)

Kailiang Bo, Zheng Ma, Jinfeng Chen, Yiqun Weng
Theoretical and applied genetics 2015 v.128 no.1 pp. 25-39
Cucumis sativus, chromosome mapping, color, correlation, cucumbers, domestication, evolution, flowering, fruits, genetic markers, genome, inbred lines, landraces, linkage groups, loci, microsatellite repeats, quantitative trait loci, China
The Xishuangbanna cucumber (XIS) is a semi-wild landrace from the tropical southwest China with some unique traits such as tolerance to low light, large fruit size and heavy fruit weight, as well as orange flesh color in mature fruits that are very useful for cucumber breeding. In this study, we investigated the genetic differentiation of XIS cucumber with cultivated and wild cucumbers as well as the genetic basis of these unique traits in XIS cucumber. We used 124 recombinant inbred lines (RILs) derived from the cross of the XIS cucumber with a cultivated cucumber line and developed a linkage map with 269 molecular markers in seven linkage groups. Comparative analysis of orders of common markers revealed that the XIS cucumber shares the major chromosomal rearrangements in chromosomes 4, 5 and 7 between the wild and cultivated cucumbers suggesting the origin of the XIS cucumber through diversification selection after cucumber domestication. Several XIS-specific minor structural changes were identified in chromosomes 1 and 6. QTL mapping with the 124 RILs in four environments identified 12 QTLs with 2 for first female flowering time, 5 for mature fruit length, 3 for fruit diameter, and 2 for fruit weight. Six of the 12 QTLs were consistently detected in all four environments. Among the 12 QTLs, six were major effect QTLs for respective traits that could explain at least 10% phenotypic variations each. Results from this study provide important information on the cytological and genetic basis of crop evolution leading to the XIS cucumber. The molecular markers associated with the QTLs should be useful in using the genetic resources of XIS cucumber in cucumber breeding.