Construction Of Chromosome Segment Substitution Lines And Localization Of QTL Related To Fruit Shape In Cucumber

Cucumber?Cucumis sativus L.,2n=14?is an economically important horticulture crop and cultivated widely in China.Fruit shape is an important factor affecting the commerciality of cucumber,and fruit shape is controlled by a series of quantitative trait loci?QTLs?and is susceptible to environmental conditions.In this study,the genes controlling fruit shape can be separated into different lines by constructing chromosome segment substitution lines?CSSLs?,so the quantitative traits controlled by multiple genes became some quality traits controlled by single-gene.The QTLs/genes related to fruit shape were identified and then the regulatory mechanisms of fruit shape were further studied.First,phenotypic variances were investigated between cucumber inbred lines CNS21 and RNS7.The two inbred lines were planted in greenhouse for two crops and our results showed that the ovary length of RNS7 was about 1 cm,the fruit shape index was 1.1¹.3,immature fruit was about 5 cm and the fruit shape index was about 1;the mature fruit had a length of 8¹0 cm and the fruit shape index was 0.7¹.0.While CNS21 displayed long and cylinder shape with the ovary length of 5⁶ cm?the fruit shape index of 10¹2?,the immature fruit length of 35⁴0 cm?the fruit shape index about 10?and the mature fruit length of 50⁶0cm?the fruit shape index about 10?.For fruit spines,RNS7 had fewer and black spines in contrast to the few and white spines of CNS21.For pericarp color,the ovaries of CNS21 and RNS7 were all emerald;the immature fruit of CNS21 was deep green,and RNS7 was viridescent;CNS21 became yellow when grew mature,but RNS7 had brown mature fruits.In addition,obvious phenotypic differences were found in seed size,leaf shape,stem shape and the shape of stamen for CNS21 and RNS7.Then the genome-wide molecular genetic map that was composed of 114 InDel?Insertion and Deletion?markers was developed by re-sequencing two cucumber inbred lines,CNS21 and RNS7.18 InDel markers were observed to be located on Chr.1,16 on Chr.2,19on Chr.3,14 on Chr.4,19 on Chr.5,17 on Chr.6 and 11 on Chr.7,respectively.The average distance between the two neighboring InDel markers was approximately 1.68 Mb.Next,CNS21?donor parent?was crossed with RNS7?recurrent parent?to produce F₁,then the backcross progeny BC₄F₁ plants were generated through four-round backcross of the F₁ plants with RNS7,and BC₄F₂ was generated by selfing of the selected BC₄F₁ lines.The InDel marker assisted selection?MAS?was performed for the backcross population and self-cross population based on the following criteria:I)the chromosome segments of RNS7were substituted by many short homologous segments from CNS21;II)the genetic background of substitution lines had high-level homozygosity with the RNS7;III)partial overlap regions existed between different substituted segments of independent substitution lines.A set of chromosome segment substitution lines was successfully constructed that contained 79 lines with 85 substituted segment covering the whole genome from the 1980BC₄F₂ population by the aid of the 114 InDel markers,73 lines within the CSSL population contained a single substituted segment,while the other six lines were observed to contain two substituted segments.Finally,19 QTLs that were associated with ovary length?OVL?,ovary diameter?OVD?,fruit length?FL?,fruit diameter?FD?,mature fruit length?MFL?and mature fruit diameter?MFD?were identified for chromosome segment substitution lines.Among these identified QTLs,12 displayed major effects and 7 displayed minor effects.In addition,5 QTLs related to pericarp color?PC?,flesh color?FC?,spine color?SC?,seed length?SL?,seed width?SW?were found.