| Heterosis is common biological phenomenon observed in many crops, utilization of heterosis is an important means to increase crop yield and to improve crop quality. The breeding experience in the past decades has shown that high heterosis was mostly obtained for a cross resulting from inbreed lines with relatively far genetic distance (GD). Many researches in variant crops indicated that the GD showed positive correlation with heterosis when the parent were selected from the same heterotic group. Molecular marker technology has proven to be powerful to estimate the GD because of its distinguishing advantages over other marker technology. Furthermore, it provided a novel and effective platform for dissection the molecular basis of heterosis.In the present study, a 2×8 diallel cross design was used with 2 Brassica napus genic male sterility (GMS) lines and 8 Brassica napus restorer lines, and 16 hybrids were obtained. Genetic diversity of the 10 inbreed lines was estimated by SSR and SRAP technologies. Two kinds of heterosis based on biomass in seedling stage and seed yield in maturity stage were investigated. The correlation between GD and heterosis was analyzed to study the feasibility for the prediction of heterosis with GD. In addition, general combining ability (GCA) was surveyed for the 10 lines. The main results are as follows:1. Genetic diversityIn total,231 and 175 polymorphic bands were amplified by 79 SSR and 39 SRAP primer pairs, respectively. Clustering analysis based on UPGMA (Un-weighted Pair Group Mathematics Average) divided the 10 lines into 2 groups in 0.76 of GD. One was consisted of the two restorer lines which were artificial resynthetic Brassica napus.. The other group was further divided into two sub-groups, and each of them comprised of 4 accessions. The result of clustering analysis was consistent with the pedigree.2. Heterosis performanceHeterosis of biomass was investigated in the seedling stage. Hybrids and their parents were cultivated using nutritious solution, and biomass weight was recorded. Three trials using a randomized complete block design were conducted in three different times. The average mid-parent heterosis for fresh weight of root was 55.5%, 30.1 % and 9.2% in the three trials, respectively. For the fresh weight of aerial part, the average mid-parent heterosis was 26.1%, 27.3% and 28.0% in the three trials, respectively.Heterosis of seed yield was investigated in the field trials. Seed yield (SY), siliques per paint (SPP),seeds per silique (SPS) and plant height (PH) showed high mid-parent heterosis for most crosses, while negative mid-parent heterosis was observed for some crosses. In average, mid-parent heterosis was 28.1%, 11.1%, 10.9% and 7.2% for SY, SPP, SPS and PH, respectively.No significant correlation was observed between heterosis of biomass weight and that of seed yield.3. Analysis of combination abilityBy analysis of variance (ANOVA), very significant differences were observed between crosses for SPP and SPS. Significant difference was observed for SY, but none for seed weight. For GCA, very significant difference was observed for SPS between the two male sterility lines, and for SY between the restorer lines. The GCA of the restorer Bing-409 was highest, and the hybrids derived from it showed good performance.For SSP, mid-parent heterosis showed significant positive correlation with the sum of GCA of parent and special combining ability (SCA). For SPS and SY, no significant correlation between GCA ,SCA and mid-parent heterosis was detected. For SY, SPP and SPS, the coefficient of correlation between SCA and GD was very small, and no significant correlation was revealed.4. Correlation analysis between GD and heterosisNo significant correlation between heterosis in the two stages and GD was detected. In a conclusion, these results suggested there will be a deep exploration to predict heterosis by the GD based on molecular marker technology.
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