Pan Yupeng, Wen Changlong, Han Yonghua, Wang Yuhui, Li Yuhong, Li Sen, Cheng Xiaomao, Weng Yiqun
College of Horticulture, Northwest A&F University, Yangling, 712100, Shaanxi, China.
Department of Horticulture, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Theor Appl Genet. 2020 Jul;133(7):2271-2290. doi: 10.1007/s00122-020-03596-y. Epub 2020 Apr 18.
The legendary cucumber inbred line WI2757 possesses a rare combination of resistances against nine pathogens, which is an important germplasm for cucumber breeding. However, WI2757 flowers late and does not perform well under field conditions. The genetic basis for horticulturally important traits other than disease resistances in WI2757 is largely unknown. In this study, we conducted QTL mapping using F and recombinant inbred line (RIL) populations from the WI2757 × True Lemon cross that were segregating for multiple traits. Phenotypic data were collected in replicated field trials across multiple years for seven traits including fruit carpel number (CN) and sex expression. A high-density SNP-based genetic map was developed with genotyping by sequencing of the RIL population, which revealed a region on chromosome 1 with strong recombination suppression. The reduced recombination in this region was due to a ~ 10-Mbp paracentric inversion in WI2757 that was confirmed with additional segregation and cytological (FISH) analyses. Thirty-six QTL were detected for flowering time, fruit length (FL), fruit diameter (FD), fruit shape (LD), fruit number (FN), CN, and powdery mildew resistance. Five moderate- or major-effect QTL for FL, FD, LD, and FN inside the inversion are likely the pleiotropic effects of the andromonoecy (m), or the cn locus. The major-effect flowering time QTL ft1.1 was also mapped inside the inversion, which seems to be different from the previously assigned delayed flowering in WI2757. Implications of these findings on the use of WI2757 in cucumber breeding are discussed.
传奇的黄瓜自交系WI2757对九种病原菌具有罕见的抗性组合，是黄瓜育种的重要种质资源。然而，WI2757开花较晚，在田间条件下表现不佳。WI2757中除抗病性外其他重要园艺性状的遗传基础很大程度上尚不清楚。在本研究中，我们利用WI2757×True Lemon杂交产生的F群体和重组自交系（RIL）群体进行QTL定位，这些群体在多个性状上分离。在多年重复的田间试验中收集了包括果实心皮数（CN）和性别表达在内的七个性状的表型数据。通过对RIL群体进行测序基因分型构建了一个基于SNP的高密度遗传图谱，该图谱揭示了1号染色体上一个具有强烈重组抑制的区域。该区域重组减少是由于WI2757中一个约10 Mbp的臂内倒位，这通过额外的分离和细胞学（FISH）分析得到证实。检测到36个与开花时间、果实长度（FL）、果实直径（FD）、果实形状（LD）、果实数量（FN）、CN和白粉病抗性相关的QTL。倒位区域内五个对FL、FD、LD和FN有中等或主要效应的QTL可能是雄全同株（m）或cn位点的多效性效应。主要效应的开花时间QTL ft1.1也定位在倒位区域内，这似乎与之前认为的WI2757延迟开花不同。讨论了这些发现对WI2757在黄瓜育种中应用的意义。
