Developmental Genetic Analysis For Meal Quality Traits Of Rapeseed (Brassica Napus L.) Across Environments

Nine parental cultivars used for the experiments were Youcai 601,Double 20-4,Huashuang 3,Gaoyou 605,Zhongyou 821,Eyouchangjia,Zhong R-888,Tower and Zheshuang 72.F₁ crosses were obtained using the complete diallel mating design with no reciprocal crosses.The seeds of parents,F₁ and F₂ were collected at 5 developmental stages(15,22,29,36 and 43d after flowering) in 2007 and 2008,respectively.Seed quality traits analyzed included protein content(PC),crude fiber content(CFC) and crude ash content(CAC) in rapeseed meal. Developmental genetic models for seed quantitative traits in diploid plants were used for analyz ing the genetic main effects and genotype×environment(GE) interaction effects from diploid embryo nuclear genes,cytoplasmic genes and diploid maternal plant nuclear genes on these traits from the two-year experimental data.The main results were as follows:1.The phenotypic means for PC and CFC gradually increased along with the developmental times of rapeseed and reached its highest value at seed maturity(43d after flowering).However,CAC in rapeseed was highest at 36d after flowering.This suggested the existence of variations for these meal quality traits at developmental times or in different years.2.The results from the unconditional variance analysis showed that PC,CAC and CFC were simultaneously controlled by genetic main effects and GE interaction effects from diploid embryo nuclear genes,cytoplasmic genes and diploid maternal plant nuclear genes. Among them,PC at 36 and 43d,CFC at 15 and 43d,CAC at 43d were mainly governed by genetic main effects,while the performance at other developmental times for these seed traits was affected by GE interaction effects,respectively.For the different genetic systems,the results showed that PC,CAC and CFC were mainly affected by maternal main effects.The additive effects were more prominent than dominance effects for all seed traits at most developmental times,thus,depending on varietal performance selection could be conducted in earlier generation(s) in rapeseed breeding programs.The results from conditional variance analysis revealed that the genetic activity especially at 16～22d was important,as the greatest number of genes for these traits were activated at this particular stage.Additionally,GE interaction effects from conditional analysis were significant for all traits at most developmental times indicating that the new expression of gene(s) was to a great extent influenced by the prevailing environment.Conditional analysis also indicated that expression of genes could be interrupted at the different developmental stages.These results confirmed that the expression of cytoplasmic genes were stable under environmental conditions.3.Heritability analysis showed that heritabilities for PC,CAC and CFC were high at most developmental times.General heritability was found to be high for PC at 36d and 43d, CFC at 15d and 43d,and CAC at 22d and 43d,while for all other developmental times the GE interaction heritabilities were more prominent.PC and CFC had higher maternal general heritabilities at all developmental times,CAC had higher embryo general heritability in the initial developmental times and higher maternal heritabilities at later stages suggesting that selection could be based on the holistic performance or maternal plants.4.Correlation analysis among the different seed traits for mature rapeseed showed that there was significant positive phenotypic correlation(r_P) or genetic correlation(r_G) between PC and CAC,while significant negative r_P or r_G was observed between PC and CFC or CAC and CFC,respectively.The results of correlations among different developmental times indicated that significant positive or negative relationships existed for the genes expressed from the different genetic systems at different growth periods.Embryo dominance main correlation(r_Do) and maternal dominance main correlation(r_Dm) were more important for PC or CFC,while embryo additive main correlation(r_Ao) and cytoplasm main correlation(r_C) were more important for CAC,as the correlation values were significant among most pairwise developmental times,r_Ao and cytoplasm interaction correlation(r_CE)were not found in present experiment.5.Heterosis analysis showed that the genetic main heterosis and GE interaction heterosis from embryo,cytoplasm and maternal genetic systems were all important for PC,CAC and CFC.Embryo main heterosis for PC at 22d,CFC at 15,22,29d,CAC at 36d,and maternal main heterosis for PC at 15 and 36d or CFC at 22,29 and 43d was important.The cytoplasmic main heterosis was not found at most developmental times,while the maternal interaction heterosis was important for all traits investigated.In general,the heterosis was found to be stable across environments in present experiment.6.The predicted values of 9 parents indicated that large differences were found in genetic main effects and GE interaction effects at 5 different development times across environments, which showed the predicted parent effects were greatly influenced by environment for almost all traits at 15d and 22d.It was suggested that in rape breeding programs,Zhongyou 821 and Eyouchangjia could be used for improving PC,Youcai 601 for reducing CFC,Huashuang 3 and Zhongyou 821 for increasing CAC according to their predicted parent effects.