ABSTRACT

To overcome the problem that the sterility of cytoplasm male sterility lines in rapeseed varies with temperature, we synthesized the double-MS line with genic male sterility (GMS) as well as cytoplasmic male sterility (CMS) of rapeseed (Brassica napus L.). In 1997, The eleven generations from Polima CMS, the thirteen generations from San2A CMS and the eight generations from CMS+GMS double sterile line are used in the experiment, the genetic model and gene effect of the fertility traits in Brassica napus L., the difference between Polima CMS and San2A CMS, and the genetic interaction of the sterile genes between CMS and GMS are studied according to the new analytic methods about the quantitative fertility traits and qualitative-quantitative fertility traits. The results showed that there was a pair of recessive major sterile genes in L17A and San2A, and three pairs of recessive major sterile genes in CMS+GMS double sterile line GCDA, but there was some linkage relationship found between CMS s1 gene and one of two GMS m1m2 genes. At the same time, genetic interaction of the sterile genes between CMS and GMS have been found through comparing Polima CMS with CMS+GMS double sterile line .some differences in genetic model and gene effect between Polima CMS and San2A CMS are found too.

INTRODUCTION

All rapeseed lines with Polima male sterility that are applied in hybrid cultivars have the problem that their sterility varies with temperature. To overcome this problem, the double-MS line with genic (GMS) as well as cytoplasmic male sterility (CMS), genic and cytoplasmic double-MS line GCDA, were synthesized(Jiana Li et al,1995b). The sterile degree and stability of new sterility line are much better than Pol-CMS lines and it can be used in the production of rapeseed.

In order to study the interaction between GMS and CMS, the genetic analysis method and specific experimental design on the qualitativequantitative fertility traits controlled by one major gene and some minor genes have been given(Jiana Li et al, 1995a,1998b). For the same purpose, the theoretical segregation ratios of the fertility genes in different segregating generations have been developed by Jiana Li et al(1998a). In the paper, based on the method and theory given in the thesis above, the genetic model and gene effect of the fertility traits in the Double-MS line and Polima CMS line as well as San2A CMS line are studied.

MATERIAL AND METHOD

In 1994, the CMS+GMS plants of Double-MS line GCDA and Polima CMS line L17A were selected to cross with their common restorer L17C, San2A CMS line L16A was crossed with his restorer L16C. From 1995 to 1997, 27 generations of the three cross-progenies (see table 1) have been obtained. In the spring of 1997, the random block experiment was carried out in the farm of our university. In the florescence, the fertility of every plant in the experiment was recorded and the actual segregation ratios were calculated (see table 1). At the same time, the fertility of each blooming flower of some plants were recorded every three days in the florescence and the degree of restoration (X1) of every plant was calculated by the ratio of fertility flowers to total flowers, After maturation, Pod ratio(X2), Seed ratio(X3), Seeds/pod(X4) and Seed weight/plant (X5) of selfing inflorescence were checked. The means of 5 fertility traits in each generations were listed in table 2. According to the analysis method of qualitativequantitative fertility traits, the group means of major genes in the segregate generations were listed in table 2 too.

Table 1 The fit tests of goodness and fertility segregation in the generations

_(0.05,1)=3.84, _(0.01,1)=6.63

RESULTS AND ANALYSIS

Tests for goodness of fit in table 1 showed the actual segregation ratios of the generations from L17A and L16A fitted the theoretical segregation ratios of a pair of recessive sterile genes well, which proved that there was a pair of recessive major sterile genes to control the fertility in Polima cms and San2A cms lines. The actual segregation ratios in the F2 and F3 generations from Double-MS line GCDA were different from the theoretical segregation ratios of three pair of recessive sterile genes, the number of the sterile plants in the F2 and F3 generations from Double-MS line GCDA was lower than the expectation, but the observation in the B2 and B2’ generations fitted the expectation well, which meant that three pairs of recessive major sterile genes controlled sterility of GCDA, but there was some linkage relationship found between CMS s1 gene and one of two GMS m1m2 genes.

Mather K. and J.L.Jinks, 1982. Biometrical Genetics, Chapman and Hall, London.

Table 2 The means of 5 fertility traits in each generation

According to the method put forward by Jiana Li et al( 1995a), the data in table 2 was analysed by the additive-dominance model of the qualitativequantitative fertility traits. The results showed that the seeds/pod of the segregate progenies from three sterile lines and the seed weight/plant of the segregate progenies from Double-MS line were suited for the additive-dominance model.

Table 3 Genetic parameter of seed/pod and seed weight/plant

Choosing some variance items related to the experiment from the reference 4(Jiana Li et al,1998b), the genetic parameters of the seeds/pod in three sterile lines and the seed weight/plant in Double-MS line were estimated (see table 3). From the table 3, the major genes to control seeds/pod showed some super-dominance in the progenies from L17A but showed partial dominance in the progenies from GCDA. The super-dominant effect and the significant negative F value had been found in the trace modification genes to affect seeds/pod, which means these super-dominant modification genes would cut down the seeds/pod when they were heterozygote. The major genes to control seed weight/plant in the progenies from Double-MS line only had additive effect, and the trace modification genes only had negative dominant effect, which means the modification genes would also reduce the seed weight/plant when they were heterozygote.

CONCLUSION

As the above-mentioned genetic model, if the cytoplasmic male sterile line which is of good sterility (which have the modification genes to reduce seeds/pod and seed weight/plant) is chosen to cross with the restorer which is of strong restoration (which have the modification genes to increase seeds/pod and seed weight/plant), the heterosis of hybrid will not be vary good because the heterozygote modification genes have a negative vigour for seeds/pod and seed weight/plant. On the contrary, if the cytoplasmic male sterile line which is not of good sterility (which have the modification genes to increase seeds/pod and seed weight/plant) is chosen to cross with the restorer which is of strong restoration, the heterosis of hybrid will be best because the homologous modification genes have a positive additive effect for seeds/pod and seed weight/plant. The theoretical results accord best with the practical experience in the rapeseed breeding.

REFERENCES

1. Jiana Li and Zhanglin Tang, 1995a. An outline of quantitative genetics, Southwest Normal University Press, Chongqing.

2. Jiana Li, Zhanglin Tang, Xuekun Zhang and Chen Li, 1995b. Breeding a genic and cytoplasmic double-MS line of rapeseed(Brassica napus L.), Plant Breeding,114:552-554.

3. Jiana Li and Peng Luo, 1998a. Study on the characteristics in segregation of the sterility genes in different generations of Brassica napus L., Journal of Southwest Agricultural University, Vol.20(4):345-350.

4. Jiana Li and Peng Luo, 1998b.Genetic analysis and experimental design on the fertility traits, Journal of Biomathematics, Vol.13(6):141-150.

5. Mather K. and J.L. Jinks, 1982. Biometrical Genetics, Chapman and Hall, London