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Title: Round fruit shape in WI7239 cucumber is controlled by two interacting quantitative trait loci with one putatively encoding a tomato SUN homolog

Author
item PAN, YUPENG - Northwest Agricultural & Forestry University
item LIANG, XINJING - Northwest Agricultural & Forestry University
item GAO, MEILING - University Of Wisconsin
item MENG, HUANWEN - Northwest Agricultural & Forestry University
item LIU, HANQIANG - Northwest Agricultural & Forestry University
item Weng, Yiqun
item CHENG, ZHIHUI - Northwest Agricultural & Forestry University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2016
Publication Date: 12/3/2016
Publication URL: http://handle.nal.usda.gov/10113/5759217
Citation: Pan, Y., Liang, X., Gao, M., Liu, H., Meng, H., Weng, Y., Cheng, Z. 2016. Round fruit shape in WI7239 cucumber is controlled by two interacting quantitative trait loci with one putatively encoding a tomato SUN homolog. Theoretical and Applied Genetics. 130(3):573-586. doi: 10.1007/s00122-016-2836-6.

Interpretive Summary: Fruit size is an important quality and yield trait in cucumber, but its genetic basis remains poorly understood. Here we reported QTL mapping results on fruit size in cucumber with F2 and F2:3 segregating populations from the cross between WI7238 (long fruit) and WI7239 (round fruit) inbred lines. Phenotypic data of fruit length and diameter were collected at anthesis, immature and mature fruit stages in 4 environments; 10 major-effect QTLs were detected for these traits. Synthesis of information from these QTLs supported two interacting QTLs, FS1.2 and FS2.1 underlying fruit size variation in the examined populations. Under the two-gene model, deviation from expected segregation ratio in fruit length and diameter among segregating populations was observed, which could be explained mainly by the interactions between FS1.2 and FS2.1, and segregation distortion in the FS2.1 region. Candidate gene search in the two QTL regions identified CsSUN, a homolog of the tomato fruit shape gene SUN, as the candidate for FS1.2. WI7239 had a 161-bp deletion in the first exon of CsSUN, and its expression in WI7239 was significantly lower than in WI7238. A marker derived from this deletion was mapped at the peak location of FS1.2. Comparative analysis suggested the melon gene CmSUN-14, a homolog of CsSUN as a candidate of fl2/fd2/fw2 QTLs in melon. This study revealed the unique genetic architecture of round fruit shape in WI7239 cucumber. It also highlights the power of QTL analysis for traits with a simple genetic basis but their expression is complicated by other factors.

Technical Abstract: Fruit size and shape is an important quality trait in cucumber breeding, yet its genetic basis remains poorly understood. In the present study, we conducted QTL mapping on round fruit shape in cucumber with F2 and F2:3 segregating populations from the cross between WI7238 (long fruit) and WI7239 (round fruit) inbred lines. Phenotypic data of fruit length and diameter were collected at anthesis, immature and mature fruit stages in four environments. Ten QTLs were detected for these traits. Synthesis of information from these QTLs supported two interacting QTLs, FS1.2 and FS2.1 underlying fruit size variation in the examined populations. Under the two-gene model, deviation from expected segregation ratio in fruit length and diameter among segregating populations was observed, which could be explained mainly by the interactions between FS1.2 and FS2.1, and segregation distortion in the FS2.1 region. Candidate gene search in the two QTL regions identified CsSUN, a homolog of the tomato fruit shape gene SUN, as the candidate for FS1.2. WI7239 had a 161-bp deletion in the first exon of CsSUN, and its expression in WI7239 was significantly lower than in WI7238. A marker derived from this deletion was mapped at the peak location of FS1.2. Comparative analysis suggested the melon gene CmSUN-14, a homolog of CsSUN as a candidate of for fruit shape/size QTLs in melon. This study revealed the unique genetic architecture of round fruit shape in WI7239 cucumber. It also highlights the power of QTL analysis for traits with a simple genetic basis but their expression is complicated by other factors.