| Fruit size/shape and fruit spine are two vital evaluating criteria for commercial cucumber fruit quality. Uncover the genetic basis of fruit size/shape and fruit spine development will facilitate the progress of marker assistance selection breeding for these two traits in cucumber.Unlike other cucurbits such as melon, watermelon or pumpkin, round fruits(L/D ≈ 1.0) are rare in commercially produced cucumbers. The genetic control of round fruit development in cucumber is largely unknown. Therefore, using two special cucumber lines WI7239 and WI7167, we plan to reveal the genetic controls of cucumber round fruit shape development.Although fruit spine is very significant for commercial cucumber fruit, the genetic controlling of spine development is still unclear. This study will use a new cucumber trichome mutant to do map-based cloning and hope to provide the target gene for fruit spine breeding in cucumber. Following illustrates the major results of this study.1. To reveal genetic control of round fruit shape in cucumber inbred line WI7239, cross between WI7238(long fruit) and WI7239(round fruit) inbred lines were made to construct F2 and F2:3 segregating populations. A genetic map with 249 markers covering 721.3 cM in seven linkage groups was constructed based on the 123 F2 individuals. Phenotypic data of fruit length and diameter were collected at anthesis, immature and mature fruit stages in 4environments; 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. Candidate gene searching 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 consistent with the peak location of FS1.2. Comparative analysis revealed the melon gene CmSUN-14, a homolog of CsSUN was a candidate of fl2/fd2/fw2 QTLs in melon.2. The Xishuangbanna(XIS) cucumber accession WI7167 also bears round fruit shape.In this study, QTL mapping approach were used to understand the genetic basis of round fruit shape in XIS cucumber WI7167.With 138 F2 plants derived from a cross between WI7167(XIS cucumber, late flowering, round fruit shape) and WI7200(cultivated cucumber, early flowering, short columnar fruit), we developed a genetic map with 267 SSR loci covering745.8 cM in seven linkage groups. Phenotypic data on mature fruit length and diameter were collected from 138 F2-derived F3 families in both greenhouse and field trials. QTL mapping identified 12 QTLs for mature fruit size traits including 6 for fruit length and 6 for fruit diameter. Synthesis of information from these QTLs supported that eight consensus and interacting QTLs(FS1.1, FS1.2, FS2.1, FS3.2, FS4.1, FS5.2, FS6.3 and FS7.1) were underlying fruit size variation in the examined populations.3. The new cucumber trichome mutant RIL-46 M exhibited a completely glabrous phenotype on all aerial organs. Genetic analysis indicated that the glabrous phenotype of RIL-46 M was inherited as a single recessive gene, csgl3. Fine genetic mapping delimited the csgl3 locus into a 68.4 kb region with 12 predicted genes. Genetic analysis, sequence alignment and allelic variation survey in natural populations identified Csa6G514870 encoding a class IV homeodomain-associated leucine zipper(HD-ZIP) transcription factor as the only candidate for CsGL3, which was 5188 bp in length with 10 predicted exons. Gene expression analysis revealed the loss-of-function of CsGL3 in the mutant due to the insertion of a 5-kb long terminal repeat(LTR) retrotransposon in the 4th exon of CsGL3. Linkage analysis in a segregating population and gene expression analysis of the CsGL1 and CsGL3 genes in csgl1,csgl3, and csgl1+3 genetic backgrounds uncovered interactions between the two genes. |
PDF Full Text Request