Genetic Analysis For Pod Weight And Rapeseed Traits (Brassica Napus L.) At Different Developmental Stages

Nine parents(Youcai 601(P₁),Double 20-4(P₂),Huashuang 3(P₃),Gaoyou 605(P₄), Zhongyou 821(P₅),Eyouchangjia(P₆),Zhong R-888(P₇),Tower(P₈)and zheshuang 72 (P₉))were used in the present investigation.Seeds of F₁,F₂ and the parents were collected at 15d,22d,29d,36d and 43d after flowering and fertilization.The unconditional and conditional genetic models and corresponding statistical approaches for quantitative traits in diploid plant were applied to analyze the genetic effects for quality traits of plant and rapeseed(Brassica napus L.)including pod weight(PW), 1000-seed weight(KSW),protein content(PC)and oil content(OC).The dynamic gene expression mechanism from different genetic systems for these traits were analyzed;and the unconditional and conditional genetic relationships between rapeseed quality traits was estimated by using developmental model approaches,which could estimate the genetic relationships between two traits.The heritability and heterosis of F₂ for corresponding traits were also determined in present experiment.The unconditional genetic model which could analyze the cumulative genetic effects at different developmental times and the conditional genetic model which could analyze the net genetic effects at the special developmental stages for quantitative traits were used to analyze the dynamic effects of genes for PW at the developmental process of rape. Among the genetic main components,the additive effects were the most important ones at most times,except for the developmental time of 22 day after flowering which the dominant effect was more active.The results of conditional genetic analysis at different developmental stages showed that there were differential expression patterns among the pod developmental stages with the most active stage being 16 - 22 days after flowering for PW.Developmental genetic models for seed traits were used to understand the dynamic expression of genes for KSW,PC and OC in rapeseed.The unconditional analysis showed that the accumulated genetic effects of genes from the different genetic systems including diploid embryo nuclear genes,cytoplasmic genes and diploid maternal plant nuclear genes were all important for the performance of studied quality traits at most developmental stages.KSW and OC at different developmental times were affected by embryo additive effects and dominance effects alternate,but the main genetic effects controlling PC were embryo additive effects at the whole developmental period.The results of different genetic systems indicated that the maternal effects were the main factors of genetic effects for KSW and PC at most developmental times.OC was mainly determined by maternal effects at 15d and 29d after flowering,but the main effects were diploid embryo ones at 22d and 43d after flowering,cytoplasm effects were main at 36d after flowering.The conditional genetic analysis indicate the stage of 37 - 43 days after flowering was the most active one for KSW among the rapeseed developmental stages, although the net genetic effects were varied at different developmental stages,while the net genetic effects of genes expressed at the developmental stages of 16 - 22 days were more important than at other stages for OC and PC.Heritabilities were all important at five developmental stages for PW,the plant selection in early generations could be effective for improving PW in rape breeding.The maternal heritabilities were the main ones at most times for KSW and PC.For OC,the heritabilities which play an important role were different in developmental times.Correlation analysis between same trait among different times indicated that there existed significant coefficients due to additive and dominant effects for PW at most times. The significant genetic correlation components were positive.While for rapeseed traits, the significant genetic correlation components among different genetic systems were different.The analysis of dynamic correlation on the sequential expression of genes during the developmental process is required for understanding the developmental genetic mechanisms of complex quantitative traits.The analysis of correlation between different pair of traits showed that most coefficients of KSW and OC were inconsistent at most times.So it is difficult improve KSW and OC simultaneously.The coefficients between KSW and PC indicated that the significant genetic correlation components among different genetic systems were mostly positive,so both quality traits of rapeseed could be simultaneously increased at different developmental times.Furthermore,the results of coefficients between KSW and PC were resembled. The results indicated that the heterosis over mid-parent value based on population mean at the stages of 29d and 36d were significantly larger than those at other stages.For quality traits of rapeseed,standard dominance genetic effects can be used to evaluate heterosis of quality traits of rapeseed.Embryo heterosis can decrease KSW of rapeseed at the stages of 15d and improve KSW of rapeseed at the stages of 36d and 43d after flowering,but improve OC at the most stages and only improve PC at the later stages. Maternal plant heterosis can decrease KSW and PC,but improve OC at the most stages. The predicted cytoplasmic effects of nine parents showed that the impacts of cytoplasmic effects of parents on KSW,OC and PC of crosses were varied.The results indicated that cytoplasmic effects of P₈ and P₉ can be used to improve KSW,but P₁ can be used to decrease KSW.Cytoplasmic effects of P₃ and P₄ were effective on improving OC,but cytoplasmic effects of P₇,P₈ and P₉ were opposite.Cytoplasmic effects of P₁ and P₉ can be used to decrease PC at the 22d after flowering,but cytoplasmic effects of other parents were not significant for PC.