| Middle and lower valley of Yangtze River is a main production and high yielding area of canola (Brassica napus L.) in China. However, canola crop in this region is always in risk of seed yield loss which is caused by water-logging damage. This risk is mainly resulted from the paddy field condition due to the cropping system of canola following rice crop and from plentiful rainfall during canola cropping season. It is of importance to study the inheritance of water-logging resistance in Brassica napus L. for canola breeding as well as canola production.In this study a method for screening of water-logging resistance lines from a large scale of samples in Brassica napus L. was set up, which was based on the method developed by li yun et al. A family line population of 6 generations of P1, F1, P2, B1:2,B2:2, F2:3 derived from the cross of WR-4 (resistant line) ×WR-5 (susceptible line), totally 433 lines in 2012 and 343 in 2013 were used as materials respectively. To identify water-logging resistance of the population, the mortality of seedling was recorded on the 7th day after logging-removing for plant recovery following 6d full-submergence treatment in two consecutive years of 2012 and 2013. Genetic segregation analysis by applying major gene plus polygene mixed inheritance model was used to search genetic behavior of water-logging resistance in family lines population. A genetic linkage map of Brassica napus L. was constructed by applying SSR and SRAP markers. QTLs for water-logging resistance were identified in population of F2:3 in the two consecutive years as well.The main result from this study was summarized as follows:1. A screening method for identification of water-logging resistance lines from a large scale of samples was set up in Brassica napus L.A method for screening of water-logging resistance lines from a large scale of samples in Brassica napus L. was set up based on the identification method developed by li yun et al. Firstly,100 seeds was selected from each line and germinated in zpetri dish with wet tissue at illumination incubator for 36h (10h light/25℃and 14h dark/20℃). While the root-tip comes out well germinated seeds were selected and transplanted to a plastic plate having 3×7 caverns on it. Each cavern planted 25 germinated seeds.Three replicates (3 caverns) were designed for each line. After that, put the plastic plate into a growth chamher. When the young seedling grown up to the stage of cotyledon open and flat,5 relatively weak seedlings were removed from each of the caverns. And 20 seedlings in each cavern left. At the same time the submerge treatments was carried out. The plastic plate together with seedlings was put into a plastic container and then pooled water into it until water surface level over the seedling top 2cm last for 6d before the water was removed. Then let the seedlings to recover in a natural condition taking regular management. The number of dead seedlings was recorded on the 7th day after water removing. This trial was carried out in the year of 2012 and 2013 respectively.2. Inheritance of major gene plus polygene of water-logging resistance in Brassica napus L.Results of inheritance of major gene plus polygene of water-logging resistance of family lines population of 6 generations in Brassica napus L. showed that the mortality of the seedling was respectively fitted the genetic model of E-0 and B-3 i.e. two pairs of additive-dominant-epistatic major gene plus additive-dominant-epistatic polygene model (2012) and two pairs, of additive major gene model (2013). This result conforms that water-logging resistance of seedling stage in this cross was controlled mainly by two pairs of major gene which expressed in the mode of additive-dominant-epistatic effects. While dominant effects expressed (2012) it gave a higher value of|ha|=0.3475,|hb|=0.0069 than the additive effect of the major genes which was|da|=|db|=0.0036. h2mg of Bi:2, B2:2, F2:3 generation in year of 2012 was 36.25%,61.40% and 61.84% respectively with an average of 53.16%. In year of 2013 it was 8.3%,30.48% and 43.13% respectively with an average of 27.30%. Variant from environment effects was 59.77% out of the total phenotypic one in the two years average. A conclusion could be made that water-logging resistance of seedling in Brassica napus L. was controlled by two major genes but heavily affected by environment. Since a higher value of h2mg was detected in B2:2 and F2:3 populations to selection it in early generations might be an effective way for water-logging resistance breeding in Brassica napus L.3. Genetic linkage map construction in Brassica napus L.A genetic linkage map of Brassica napus L. was constructed by 75 SSRs and 66 SRAPs which was made up of 20 linkage groups covering 1374.21 cM in total with an average interval of 12.1cM.4. Mapping QTLs for water-logging resistance in Brassica napus L.Results of identification of water-logging resistance of family lines population of 6 generations in Brassica napus L. showed that the seedling mortality of WR-4 and WR-5 was 31.0%(22.3%-39.7%) and 72.1%(67.0%-77.2%) respectively showing a significant difference between them. The mortality of F2:3 were 63.77% in average showing a skew distribution. Totally, eight QTLs of water-logging trait detected in the two years. Among them, five including qWR1, qWR5, qWR.9-1, qWR9-2 and qWR17 located on the linkage population of LG1, LG5, LG9, LG17 explaining 2.24% to 47.58%phenotypic variation in 2012 and three QTLs including qWRl, qWR9-1, qWR9-2 located on LG1, LG9 explaining 3.02%to 23.57% phenotypic variation in 2013. However, qWRl, qWR9-1, and qWR9-2 could be detected repeatedly in the two years test explaining 3.03%,15.87% and 35.57% phenotypic variation respectively. It indicates that qWRl, qWR9-1 and qWR9-2 were the loci associated with water-logging resistance trait. While qWR9-1, qWR9-2 could be the two major QTLs controlling inheritance of the trait in Brassica napus L. |
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