| Genetic systems of major agronomic and quality characters in Brassica napus L. were studied by means of a joint segregation analysis in a multi-family generation (P,, F,, P2, B, 2, B22 and F2.3) of HSTC14 x Ningyou 7 and a comparison of major loci groups of a diallel crossings derived from 12 parents which are carefully selected from China, Belgium, Sweden, Canada, Australia and Japan. Potential and strategy of further improving of heterosis were investigated. Practical improvement of heterosis was conducted based on Dudley's method using an elite hybrid, Ningza l,as an example. The main results are as follows:1. The genetic system of erucic acid content of HSTC14 x Ningyou 7 was analyzed. HSTC14 has an erucic acid content of 1.285%, and Ningyou 7 has that of 44.468 %. On the basis that erucic acid content was controlled by two pair of genes which was concluded by earlier research found that genetic system of this trait was formed by two pair of major genes plus multi-pair of polygenes resulting from this study. Two major genes act mainly in the manner of additive and dominance, as well as in the manner of additive x additive, additive x dominance, and dominance x dominance. A big difference in gene effect was found between the two pair of major genes. Polygene acts in the manner of additive-dominance. Genetic variation of the major gene(s) in F2;3 population is 51.33% of the total phenotypic one. That of multi-gene accounts 47.81%, indicating that only 50% more of erucic acid content is determined by the major genes and the effect of interaction of the two major genes and the effect of multi-genes play an important role in performance of erucic acid in Brassica napus.Day to flowering (DTP) of HSTC14 and Ningyou 7 is 42.50 (d) and 31.80 (d) respectively. Although the two parents have a big difference in DTP, but the cross is not the earliest and latest DTP combination. Genetic system of DTP of the cross consists of onepair of major gene and multi-pair of polygenes. Both of major genes and polygenes act in the manner of additive and dominant. In F2:3 family populations, hereditability of the major genes (h2mg) are 46.59%, and that of polygenes (h2pg) 16.00%. About 37.41% of the phenotypic variation of DTP is attribute to environmental factors. Dominant effect of major genes is negative (h =-7.0425), much higher than additive effect (d - 1.4694) indicating that early flower is dominant to late flower in this cross.1000 seed weight of the two parents is 3.149 ?O.Olg and 3.759 ?0.042g respectively. There is a big difference found, but it is not the combination of the two parents, one has the smalleslOOO seed weight and the other is the biggest one. Genetic system of 1000 seed weight consists of one pair of major gene plus polygenes in the cross. Only found the additive effect in major genes. Effect of polygenes acts in the manner of additive and dominant. Hereditability of major genes (h2mg) in F2;3 population is 83.39%, and that of poly-gene (7z2pg) is 11.71%. A small variation of polygenes intra-population could be resulting from linkage. There is no heterosis for 1000 seed weight in the cross because of no dominant effect found in major genes though the major genes playing an important role in the genetic system of 1000 seed weight.2. Genetic difference of seed yielding per plant, seeds per pod, 1000 seeds weight, pods per plant and flowering time (DTP) were studied in a diallel cross population of 12 Brassica napus varieties by applying the method of major loci group plus minor loci group analysis.Genetic system of seed yielding per plant of the 12 parents consists of 3 major loci groups plus mini loci group. Gene effect of the 3 major loci group is not equal. Additive effect (du) is - 4.8941", 2.2821* and 0.5183,and dominant effect (hM) is 4.230", 5.5327" and 4.7743" respectively. hM showed a high and positive value indicating that it will increase seed yielding per plant when the major loci are all heterozygous. Percentage of genetic variability of major loci groups (H2mg) is 44.07%. Abo...
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