| Shoot branching greatly contributes to plant architecture. Usually, shoot branching influences crop yield by bringing about a variation in the number of fruits (grain), and also by altering the nutrient distribution in crops.Comparing with other plants, molecular biology studies on cucumber are dropping behind, especially in lateral branch-related traits. In this study, all the researches were related to cucumber lateral branching:First, a group of 224 recombinant inbred lines (RILs) was derived from a narrow cross between 2 cucumber (Cucumis sativus L.) lines, namely, S94 (Northern China type with weak lateral branch growth potential and early lateral branch sprouting time) and S06 (Northern European type with strong lateral branch growth potential and late lateral branch sprouting time). These lines were then used for investigating lateral branch-related traits. A total of 36 quantitative trait loci (QTLs) were detected for the following 4 lateral branch-related traits (lateral branch average length (LBAL), lateral branch total length (LBTL), lateral branch number (LBN), and first lateral branch node (FLBN). Further, each QTL explained 3.1% (lbtl2.1, spring) to 32.3% (lbn2.3, spring) of the observed phenotypic variance. Eleven QTLs (lbal1.1, lbtl1.1, lbn1.2, flbn1.2, etc.) for different traits were found to be clustered on the e23m18d-ME23EM6c section (7.4 cM) of linkage group (LG) 1; further, 15 QTLs (lbal2.1, lbtl2.1, lbn2.1, flbn2.1, etc.) were found to be clustered on the S94A1-ME4SA4a section (13.9 cM) of LG2. Twenty-one QTLs explained more than 10% of the phenotypic variance. Moreover, lbtl1.3 (autumn, 26.2%, logarithm of odds (LOD) = 17.4; spring, 26.9%, LOD = 17.9) had stable position and contribution in both seasons. Several sequence-anchor markers (CMBR40, F, CS30, S94A1, CSWTA11B, etc.) were closely linked with some QTLs for LBAL, LBTL, LBN, and FLBN, which can be used for the marker-assisted selection to improve the plant architecture in cucumber breeding.Secondly, several cucumber lines, one without lateral branching and others with lateral branching, were investigated in this study. The comparison results revealed that axillary meristems in all axils of S61 had developed to flower buds, so there were no lateral branches in the axils of this cucumber line. When the growth condition (such as tempreture and illumination) was changed, inflorescence could reverse to lateral branch. Anatomy researches have been taken on two types of cucumber lines (with/without lateral branching). The comparison results showed that the axillary meristems in cucumber axils were coessential at the early stage of development. The fate of axillary meristems of cucumber was determined mainly by hereditary factors, but changing environment in this stage could also alter the fate of axillary meristems. Therefore, we presumed that the non-lateral branch phenotype of S61 was due to the genetic variation in vegetative bud formation stage.Thirdly, the non-branching cucumber line S61 was intercrossed with several branching cucumber lines. The plants of the F1 generation were self-pollinated to obtain F2 progenies, or were backcrossed with S61 to obtain BC1 progenies. The segregation ratio of branching and non- branching phenotype in F26106 was approximate 3:1, and in BC16106 was approximate 1:1. It proved that there was a pair of dominant/ recessive allele which controlling lateral branching formation in cucumber lines S61 and S06. This gene was named NLB(non-lateral branch)gene. And bulked segregant analysis was used for gene mapping. Two SSR markers and one SRAP marker were mapped on one side of nlb. The two SSR markers, CMBR40 and CMBR97, were located at the same position. And the genetic distance between nlb and CMBR40 was 28.8cM, between nlb and the SRAP marker me5em3 was 25.2cM. This nlb gene was located on LG1 of the cucumber genetic linkage map by using 3 anchor markers. |
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