Genetic Analysis For Growth Period Structure Traits And QTL Mapping Of Relative Genes In Soybean

Growth period traits of soybean include not only the whole growth period (M), but also the growth period structure, i.e., the relative length of various developmental phases. In this study, the inheritance and QTL mapping of the growth period structure traits of soybean were analyzed based on segregation population derived from parents having similar M and different V, and the inheritance of the length of reproductive period (R) and the sensitivity of agronomic and quality traits to post-flowering photopeirod were also analyzed using the population derived from the parents with similar V and different M. The results were summarized as follows:1. The inheritance of growth period structure traits in the cross with parents having different V and M.Joint segregation analysis based on P₁, P₂, F₁, F₂, F_2:3 generation populations derived from Xiaoheidou and GR8836 indicated that one major gene modified by poly-genes controlled the traits of V, M and R/V ratio. The major gene heritability was 77.59%, 16.77% and 54.68%, respectively. The major effect gene had positive addictive effect for V and M, and negative addictive effect for R/V. Since the major gene of R/V and V had higher heritability, then it will be effective to select the genotypes with desirable growth period structive traits.2. QTL mapping for growth period structure traits in soybean.F₂, F_2:3 populations derived from Xiaoheidou and GR8836 were grown in spring and summer to map the relative genes of growth period structure traits and photothermal response sensitivity. One major effect QTL closed to Satt557 on C2 linkage group was detected, which associated with R/V ratio, V and M under different planting seasons. It was shown that the major effect QTL was stable in different environments. Meanwhile, the phenotypic variance explained by QTL, addictive and dominant effects were different for each trait, and seven minor effects QTL for growth period triats were could not be detected repeatedly under different planting seasons. Those indicated that genes of growth period traits were influenced by environmental factors to a certain extent. One major effect QTL for photothermal response sensitivity of R/V was mapped, which associated with the marker of Satt286 lied on C2 linkage group. To find the relationship of major effect QTL and E-series matutity genes controlling flowering and maturity time, Satt557 and Satt365 were used to assay the banding pattern of 41 NILs. The results indicated that the major effect QTL mapped in this study was tightly linked to E1/e1.3. Distribution of major QTL in different maturity groups soybean varieties.The banding patterns of 38 American varieties and 64 Chinese varieties belonging to different maturity groups were assessed using the SSR primers of Satt557 and Satt365 tightly linked to the major effect gene of growth period structure traits. The results suggested that the distribution frequency of major effect gene in American varieties was higher than that in Chinese varieties. Meanwhile, the percentage of varieties carring recessive allele to all varieties carring major QTL was higher in American maturity group varieties than that in Chinese, and the recessive allele mainly distributed in the early maturity groups, indicating that the recessive allele was more frequently used in American varieties than in Chinese varieties.4. Evaluation of the effects of major maturity gene E1/e1 and its dependence on photothermal environment.Effects of E1/e1 on growth period structure traits under different photoperiods and planting seasons were investigated by using maturity near-isolines of soybean. Dominant allele of E1 delayed V and M, hastened R and decreased R/V in most genotypes studied. Gene effect was dependent on the genetic background as well. There were interactions between E1 and other matrutiy genes since the dominant allele could strengthen the effects of other maturity genes generally. The interaction between E1 and environment was also detected, E1 effect under long day (LD) was higher than under short day (SD), and that in spring sowing was higher than in summer sowing.5. The inheritance of R and R/V in the cross with parents having different (M) and similar (V).Joint segregation analysis based on populations derived from Ludou 9 and Zhejiangsiyuebai showed that R was controlled by one major gene plus poly-genes. Heritability of the major effect gene was 44.11% in F2 generation; R/V was controlled by two major genes modified by poly-genes. Total heritability of two major genes was up to 82.37%. The addictive effects of two major genes were all positive. It was proposed that R/V ratio could be selected in early generations.6. QTL mapping and effect analysis of yield and quality traits in soybean under different post -flowering photoperiods.181 recombinant inbred lines (RIL) derived from Baohexuan 3×Xuyonghongdou were constructed to map QTL associated with the agronomic and quality traits under both LD (16 h) and SD (12 h) and their photoperiod response sensitivity. The order of the photopeiod sensitivity of the following eight traits was as below: reproductive period length (R)>plant height>node number on the main stem>protein content, oil content>100-seed weight>pod number per plant>total percentage of protein and oil. By using MCIM method, a total of 21 QTL were identified and mapped on 11 linkage groups including A1, A2, B1, B2, C1, D1a, etc. QTL detected could explain 5.83%～21.44% of observed phenotypic variation. For the given agronomic or quality traits, no major QTL were explored both under SD and LD. It could be drawn that photoperiod sensitivity is the key trait for adaptability improvement of soybean. To breed elite varieties with ideal yield potential, quality and stress tolerance, the photoperiod-insensitive genes related to various traits should be explored and pyramided with other needed genes.