Genetic Dissection Of The Early Flowering Trait Of Two Inbreed Lines In Rapeseed (Brassica Napus L.)

Rapeseed（Brassica napus L.）is not only one of the main oilseed crops around the world,but also the biggest oilseed crops in China.So,high and stable yield of rapeseed has special significance to Chinese edible oil security.Yangtze river basin is the main production area of rapeseed.But the conflicts of summer corps（rice and maize）and winter rapeseed is increasingly prominent with the changing of faming systems.Thus,breeding early flowering and high yielding rapeseed cultivars is one of the most urgent breeding targets in the Yangtze River basin.At the same time,northwestern China belongs to one year plant system area,do not exist stubble conflicts,but exist short frost-free season contradiction.The breeding of cultivars with both early maturity and high yield is one of an urgent target of rapeseed breeding.Thus,exploring new flowering time genes is of great importance to shorten the whole growth period in rapeseed.In this study,we dissected genetically the flowering time variation of the elite parents 616A and R11,via a DH population and QTL mapping method,and discovered main effective genes（QTL）which can control the flowering time of rapeseed.Simultaneously,the natural variations of these main effective genes（QTL）were introgressed into 616A genetic background by marker assistant selection,and eight near-isogenic lines with the permutations of the genes（QTL）were developed subsequently.At last,these near-isogenic lines were used to develop near-isogenic hybrids and NCⅡpopulation,and field experiments were carried out both in winter rapeseed and spring rapeseed environments respectively,for exploring how the flowering time genes（QTL）affect the comprehensive agronomy traits,especially yield.The main results of this study were as followed:1.Genetic dissection the early flowering time characters of 616A and R11Via the analysis of the flowering time variation of the DH population developed from the F₁ of 616A and R11,we demonstrated the allelic variations Bnflc.a2 and Bnflc.c2 of BnFLC.A2 and BnFLC.C2 were the genetic reason of early flowering time of R11;while the allelic variation qft.a3 of QTL qFT.A3 was the genetic reason of early flowering time of 616A.The further research indicated that BnFLC.A3b might be the candidate of qFT.A3.According to the sequence variations of the two parents,we developed a special amplified SCAR mark of BnFLC.A3b,which laid the laid the foundation for the follow-up research.2.Development of the 8 near-isogenic lines with allelic permutations of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）of 616A genetic background.The 8 near-isogenic lines with allelic permutations of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）were developed by an integrated strategy including marker assisted selection and backcrossing.These near-isogenic lines were named as ID01-000,ID02-010,ID03-001,ID04-100,ID05-011,ID06-110,ID07-101,and ID08-111,respectively.Thereinto,ID01-000 had the mutated alleles at all the three loci;ID08-111 had all the wild alleles at all the three loci;ID02-010,ID03-001 and ID04-100 had the mutated alleles at any two loci of the three genes;and ID05-011,ID06-110 and ID07-101 had only one mutated allele at any these three loci.Additionally,both restore lines and sterile lines were developed for each of the 8 near-isogenic lines.Thereinto,the fertile lines（i.e.,the restore lines）were used in the post research.3.Phenotypic observation of the 8 near-isogenic linesNo matter in the winter rapeseed environment or in the spring rapeseed environment,the flowering time of the 8 near-isogenic lines showed a gradient variation.The broad‐sense heritability of flowering time was 0.8605,indicated the flowering time of the 8near-isogenic lines can be inherited stably.Except for flowering time,the comprehensive traits of the 8 near-isogenic lines variated also widely,either,especially the yield.ID01-000 flowered earliest and had the lowest yield,while ID08-111 flowered latest and had the highest yield.ID02-010,ID03-001 and ID04-100 flowered significantly earlier than ID05-011,ID06-110 and ID07-101,and had significantly lower yield than the latters.In addition,correlation analysis indicated that the flowering time and the yield were significantly positive correlated.4.Additive effects of BnFLC.A2、BnFLC.C2、qFT.A3（BnFLC.A3b）To explore the reason why the yield decrease was associated with early flowering time,we analyzed the additive effects of BnFLC.A2、BnFLC.C2、qFT.A3（BnFLC.A3b）on the flowering time and the yield.The results indicated that the additive effects of BnFLC.A2、BnFLC.C2、qFT.A3（BnFLC.A3b）on flowering time were 13.34d,8.571d,and 9.380d,respectively.While their additive effects on yield per plant（PY）were 1.446g,1.365g,and 1.361g,respectively;and their additive effects on yield per hectare（HY）were 207.7 kg/ha,198.1 kg/ha,193.7 kg/ha,respectively.Thus,the additive effect of flowering time genes（QTL）was the genetic reason why yield decrease was associated with early flowering time.5.Heterosis and non-additive effects analysis of BnFLC.A2、BnFLC.C2、qFT.A3（BnFLC.A3b）To explore the heterosis and non-additive effects of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）,the 8 near-isogenic lines were mutual crossed to develop the 19near-isogenic hybrids.The field environment results showed that all of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）had yield heterosis,especially the genotype heterozygous at all three loci.Non-additive analysis indicated that the dominant effects of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）on PY were 3.504g,2.991g,and3.284g respectively,much higher than their additive effects;while for flowering time,the dominant effects were 0.647d,-1.263d,and-1.074d respectively,far lower than their additive effects.Simultaneously,the dominant×dominant×dominant epitasis effect of the 3 genes（QTL）was 4.393g,acted as a yield facilitating factor.This indicated when the dominant effects of BnFLC.A2,BnFLC.C2,and qFT.A3（BnFLC.A3b）facilitated yield heterosis,but they affected very limited to flowering time.Thus,utilization of the heterosis and non-additive effects of flowering time genes（QTL）themselves to compensate for the yield loss induced by the negative additive effects could be feasible genetically.6.Heterosis and non-additive effects analysis of BnFLC.A2,BnFLC.C2,qFT.A3（BnFLC.A3b）For proving the above results furtherly,an NCⅡpopulation was developed by the elite restore lines ZS4R and 621R,and the 8 near-isogenic lines.The field experiment results indicated that the non-additive effects of the flowering time genes on PY and HY were significant,and the highest non-additive effects occurred when BnFLC.A2,BnFLC.C2,qFT.A3（BnFLC.A3b）were all heterozygous.Additionally,the heterosis was the highest when BnFLC.A2,BnFLC.C2,qFT.A3（BnFLC.A3b）were all heterozygous.Multiple comparisons showed no significant difference on PY and HY between the early flowering hybrids heterozygous the all the three loci and the late flowering hybrids of SG128 and SG136.This indicated heterosis and non-additive effects really brings the positive gain of yield and could compensated for the yield loss induced by early flowering in the NCⅡdesign population.Thus,taking full use of the heterosis and non-additive effects of flowering time genes in the breeding of early flowering time hybrids is of great significance to achieve the goal of early flowering time with high and stable yield.