Cytogenetic Studies On Fertility In New-tetraploid Rice Hybrids

Autotetraploid rice is a diploid rice germplasm obtained by chromosome doubling of colchicine.F₁,a hybrid of indica and japonica autotetraploid rice,has obvious biological advantages,but its fertility is generally low and can not be directly used.In this experiment a new type of tetraploid rice（neo-tetraploid rice）was successfully bred by using different types of autotetraploid rice and multi-generation directional selection.This rice not only has high fertility,but also can overcome the sterility of hybrid F₁.That is to say,the hybrid F₁with low fertility autotetraploid has normal fertility,and the yield advantage can be exerted,showing a broad utilization prospect.In order to understand the cytogenetic mechanism of high fertility in a new type of tetraploid hybrid rice F₁,a new type of hybrid rice F₁was crossed with a low fertility autotetraploid rice,the meiosis behavior,dominance behavior and possible genetic mechanism of F₁pollen mother cell were studied.The main findings are as follows:（1）Studies on fertility and cytogenetics of a neo-tetraploid rice hybrid（T485×H8）F₁The pollen fertility of the neo-tetraploid rice hybrid F₁was the highest（83.7%）,and its parents were 61.18%（T485）and 69%（H8）,respectively.The embryo sac fertility of F₁,H8 and T485 were 87.01%,83.65%and 81.82%,respectively,and the embryo fertility of F₁hybrid and its parents were similar and normal by WE-CLSM（laser scanning confocal microscope）.The meiotic behavior of pollen mother cells（PMC）during meiosis was studied by chromosome flaking technique.The results showed that the meiotic behavior of F₁hybrids was similar to that of their parents,all experienced 9 periods:prophase Ⅰ,metaphase Ⅰ,anaphase Ⅰ,telephase Ⅰ,prophase Ⅱ,metaphase Ⅱ,anaphase Ⅱ,telephase Ⅱ and tetrad.However,there were some abnormalities in different stages,such as polyvalent,chromosome dragging,backwardness,micronucleus and mitosis.In the tetrad stage,the abnormal frequency was F₁（1.08%）<H8（0.67%）<T485（0.48%）;in the metaphase Ⅰ,the abnormal frequency was T485（13.7%）<F₁（14.1%）<H8（19.6%）;in the anaphase Ⅰ,the abnormal frequency was H8（4.59%）<F₁（6.4%）<T485（6.49%）;The micronucleus rate of telephase Ⅰ was H8（1.31%）<F₁（1.62%）<T485（4.01%）,and the non-synchronization rate of telephase Ⅱ was H8（8.97%）<F₁（9.58%）<T485（13.53%）.Through the investigation of polyvalent,bivalent and univalent in pachytene and metaphase Ⅰ,the main results are as follows:In the final transition period,F₁configuration:（1.62±0.22）Ⅰ+（8.71±0.40）Ⅱ+（0.33±0.06）Ⅲ+（6.84±0.73）Ⅳ+（0.01±0.01）v+0.07±0.03)Ⅵ;H8:（1.69±0.23）Ⅰ+（8.48±0.41）Ⅱ+（0.16±0.04）Ⅲ+（7.13±0.67）Ⅳ+（0.15±0.02）v+（0.10±0.01）Ⅵ;T485configuration:（2.07±0.20）Ⅰ+（9.45±0.45）Ⅱ+（0.17±0.05）Ⅲ+（6.45±0.63）Ⅳ+（0.03±0.02）v+（0.10±0.03）Ⅵ;in metaphase Ⅰ,F₁configuration:（2.43±0.25）I+（8.27±0.36）Ⅱ+（0.46±0.07）Ⅲ+（6.7±0.83）Ⅳ+（0.07±0.04）v+（0.04±0.02）Ⅵ;H8configuration:（2.49±0.25）Ⅰ+（7.7±0.39）Ⅱ+（0.45±0.07）Ⅲ+（6.9±0.87）Ⅳ+（0.04±0.02）v+（0.05±0.03）Ⅵ;T485configuration:（2.26±0.18）Ⅰ+（9.27±0.32）Ⅱ+（0.51±0.07）Ⅲ+（6.27±0.54）Ⅳ+（0.05±0.02）v+（0.06±0.02）ⅥIn conclusion,there were some correlations among chromosome dragging,lagging,micronucleus and mitotic dissynchrony in the three materials.There were more bivalents and tetravalents in the three materials,and less other configurations.（2）Heterosis and related genetic mechanism of neo-tetraploid rice F₁The agronomic traits of neo-tetraploid rice F₁and its parents were investigated and analyzed.The mean values of plant height,seed number,1000-grain weight and seed setting percentage of F₁were significantly higher than those of its parents.Compared with the parents（T485）,the increases were 53%,122.36%,16.84%and 62.99%,respectively,the increase rates were 3.52%,55.54%,2.57%and 24.96%,among which the real grain number was the highest.Plant height,the seed number,1000-grain weight and seed setting percentage of F₁hybrid had obvious heterosis,among which the maximum were 151cm,693grains,42.08 grains and 85.26%,the minimum were 123cm,312 grains,36.32 grams and71.89%,and the coefficient of variation were 4.43%,17.04%,3.13%and 4.04%,respectively.The parent heterosis is the largest in the number of real grains per plant.It was concluded that the hybrid F₁between neo-tetraploid rice and autotetraploid rice had high fertility and obvious heterosis,especially the heterosis related to yield;the high fertility may be related to the lower chromosome abnormality behavior during meiosis.The results show that the new tetraploid rice has potential application.