Cytogenetic Studies On Neo-Tetraploid Rice And Hybrids

Autotetraploid rice is a rice germplasm obtained by doubling chromosomes from diploid rice.Compared with the diploid rice,the doubling autotetraploid rice exhibited biological advantages such as increased grain weight,thickened stems,and deepened leaves.However,the reduction in the number of tillers and the decline in seed setting rate limit the application of autotetraploid rice in production.After more than 10 years of hard work,our laboratory has selected the Neo-Tetraploid rice with high fertility and stability.The hybrids obtained from hybrids of this material with low fertility autotetraploid rice have obvious yield advantages and show a broad application prospect.In order to understand the cytogenetic mechanism of the high fertility of the novel tetraploid rice and its hybrid F₁,this study used the low fertility autotetraploid rice（T449）as a control for the novel tetraploid rice and its hybrid F₁ pollen.The chromosomal behavior of the mother cell during meiosis is further studied.The main findings are as follows:（1）Main agronomic traits and pollen fertility of the Neo-Tetraploid rice hybrid F₁and its parents.The seed setting rate of T449,the number of solids per plant and the plant height were 20.55%,127 and 87.40cm,respectively.The seed setting rate of H₁,the number of solids per plant and the plant height were 69.75%,421 and 102.50cm,respectively.The number of plant per plant and plant height were 83.12%,757 grains and 116.44cm,respectively.Compared with T449,H₁ and F₁ were higher than T449 in plant height,flag leaf length,main panicle length,effective panicle number,grain length,grain width,1000-grain weight,number of seeds per plant,and seed setting rate.High,single-grain grain number,seed setting rate reached a very significant level.The new tetraploid rice hybrid F₁ has super-parental advantages in plant height,total grain number per plant,seed setting rate and so on.The pollen fertility of T449,H₁ and F₁ were 35.10%,77.95%and77.01%,respectively.Compared with T449,the H₁ and F₁ rose by 122.08%and 119.40%,respectively,and reached a very significant level.The rate of pollen failure,pollen loss and pollen breakdown in T449 were 5.46%,46.15%and 13.29%,respectively.H₁ and F₁ were significantly lower than T449 in typical pollen rate,and were significantly lower than T449in pollen rate and pollen failure rate.（2）Chromosome Behavior of the Neo-Tetraploid rice hybrid F₁ and its parents.The process of meiosis of T449,H₁ and F₁ pollen mother cells were basically the same,and all experienced nine periods of early stage I,middle stage I,late stage I,terminal stage I,early stage II,middle stage II,late stage II,late stage II and tetrad stage.The type and frequency of chromosomal abnormalities are not the same in each period.During the quadrant period,the three material abnormalities were:F₁（1.01%）<H₁（1.06%）<T449（1.97%）.In the remaining eight periods,the three material abnormalities were:H₁<F₁<T449。Among them,the intermediate I chromosome towing rate was:H₁（1.63%）<F₁（16.18%）<T449（26.34%）;the backward I chromosome retrogradation rate was:H₁（4.96%）<F₁（7.23%）<T449（27.36%）;the end of the micronucleus rate was:H₁（0.47%）<F₁（3.47%）<T449（22.94%）;the final phase II chromosome separation asynchrony rate was:H₁（5.59%）<F₁（6.98%）<T449（27.31%）;T449 spindle abnormality rate was 4.02%at the end of phase II,H₁ and F₁ found no spindle abnormalities during this period.Regardless of whether in the final metaphase or metaphase I,as compared with T449,the number of diploids of H₁ and F₁ is high,and the frequency of univalent,trivalent,pentavalent,hexavalent is low or zero.At the final stage:the T449 configuration was:（3.29±0.25）Ⅰ+（5.56±0.36）Ⅱ+（1.27±0.12）Ⅲ+（7.22±0.17）Ⅳ+（0.11±0.03）Ⅴ+（0.06±0.02）Ⅵ;H₁ configuration:（0.59±0.12）Ⅰ+（6.10±0.34）Ⅱ+（1.28±0.20）Ⅲ+（7.84±0.18）Ⅳ;F₁ configuration:（0.49±0.16）Ⅰ+（9.18±0.45）Ⅱ+（7.28±0.23）Ⅳ.In the metaphase I:（4.19±0.40）Ⅰ+（5.30±0.45）Ⅱ+（1.30±0.18）Ⅲ+（7.21±0.30）Ⅳ+（0.05±0.03）Ⅴ+（0.04±0.02）Ⅵ;The H₁ configuration is:（2.51±1.03）Ⅰ+（6.53±0.62）Ⅱ+（0.92±0.29）Ⅲ+（7.42±0.39）Ⅳ;The F₁ configuration is:（0.69±0.13）Ⅰ+（12.65±0.54）Ⅱ+（5.49±0.27）Ⅳ.In summary,the Neo-Tetraploid rice and its hybrids show strong biological advantages,showing a broad application prospects.The fertility of the mature pollen of tetraploid rice was insufficient as evidence of its low seed setting rate.The frequency of pollen mother cellsinmediumⅠchromosomedragging,lateⅠchromosomebackward,lateⅠmicronucleus,late phaseⅡchromosome dissociation and spindle abnormality was correlated with the seed and hybrid seed setting rate.The frequency of univalent,trivalent and higher valences in pollen mother cells with high seed-bearing rate is lower in meiosis process,the frequency of bivalents is higher,and the frequency of tetravalent bodies is generally higher.