| Low-light intensity stress is one of the major limiting factors for cucumber protected cultivation in north of China, and an effective method to resolve this problem is breeding and applied to the low-light intensity tolerance varieties.The low-light intensity condition was simulated by block light net. A linkage map of cucumber was constructed using 150 progenies of F2 generation derived from a cross between the low light stress tolerance line M22 and the low light sensitivity line M14 (identified by our research group) in the experiment. The effects of low light stress on the Low-Light tolerance related traits of cucumber were investigated in a set of 123 F2:3 lines in the seeding stage in the autumn of 2008 and spring of 2009. QTL analysis was undertaken on the basis of a genetic linkage map of the corresponding F2 population that was constructed using composite interval mapping. Aims of this study were expatiating the heredity mechanism and QTL effects of cucumber low-light intensity tolerance at seedling stage, and finding genes controlling the low-light intensity tolerance and related traits, which will provide theoretic basis for genetic improvement on low-light intensity tolerance in cucumber. The main results were as below:Firstly, a genetic linkage map including 5 linkage groups base on SRAP and SSR markers was constructed using composite interval mapping, and total length was 483.9 cM, a mean interval was 4.1 cM.Secondly, total 12 SSR makers were distributed on 5 linkage groups respectively (LG1:3, LG2:3, LG4:2,LG6:2, LG7:1). Four traits such as low-light intensity index, chl content, hypocotyl length and hypocotyl thick were investigated in a set of 123 F23 lines at seedling stage in the Autumn of 2008 and Spring of 2009. QTL analysis was undertaken based on a constructed genetic linkage map of the corresponding F2 population. Total 12 QTLs controlling these traits were detected and a major locus of every traits with contribute ratio of over than 10%, details as below:1) Total three QTLs of low-light intensity tolerance index were detected and they distributed on LG1 and LG2, explained phenotypic variation of 9.6%,13.6% and 10.8% respectively. Among them, QTL Lltil.1/ Lltil.2 located on LG1 and QTL Llti2.2 located on LG2 were additive loci, and QTL Llti2.3 located on LG2 was sub-effect locus. 2) Three QTLs controlling Chl content were located on LG 2, LG4 and LG7, and the phenotypic variation explained by QTLs Chl were 17.3%,14.9% and 16.5%. Among them, QTL Chl2.2 located on LG2 was additive loci, QTL Chl4.2 located on LG4 and QTL Chl7.2 located on LG7 were sub-effect locus.3) The total phenotypic variation explained by 4 QTLs of hypocotyl length was 48.3%, located at 2.1/3.1,16.6/17.2,7.1/7.6 and 3.0/8.6 cM on LG6. Different effect of QTL was detected in both seasons, in which, QTLs in first season were sub-effect, and the second ones were add-effect loci.4) Two QTLs for hypocotyl thick were mapped at 40.9/47.8 cM on LG1, explaining variation of 11.2% or 10.5%, and the other QTL Hyt6.1/Hyt6.2 was at 14.3/24.7 cM on LG6, explaining variation of 16.3 or 16.5%.3 QTLs detected in two seasons all were add-effect locus, which made hypocotyl become thick.Two different QTL clusters were mapped and some traits aggregated at 5.5 cM, for example, in both seasons, QTLs for low-light intensity index and hypocotyl thick were located between ME1EM8-ME2EM8 interval and QTLs of low-light intensity index and hypocotyl length were detected in interval ME1EM6-ME2EM3. It was proved that the multi-effect of QTL by the phenomenon that different low-light intensity tolerance traits were controlled by same gene loci.QTLs of low-light intensity related traits detected in this study were more credible and molecular markers linkaged these QTLs may be useful in marker-assisted breeding in cucumbers and improve this complex trait of cucumber low-light intensity tolerance. |
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