Effects Of Seed Maturity On Seed Vigor Of Conventional Japonica Rice

Rice(Oryza sativa)is one of the main food crops.The quality of its seeds is great significance for the increase of yield.As an important indicator to measure the quality of seeds,seed vigor has received extensive attention from seed researchers.In the process of rice breeding and seed production,genetic factors and environmental conditions have an important effects on the formation of seed vigor.In this paper,five conventional japonica rice varieties of‘Chunjiangnuo 6’,‘Shaonuo 9714’,‘Xiushui 121’,‘Xiushui 14’and‘Zhejing 70’were selected as materials.Each variety was harvested on the 15th day after flowering period,the samples were taken every 5 days,and take normal harvested seeds as a control.By the measuring of the moisture content of fresh seeds,1000-grain weight,indoor germination test and field seedling emergence experiment,the optimal harvest period of the seeds of each rice variety was preliminarily determined.Based on the above results,the physiological and biochemical indexes and the expression of related enzyme genes of three rice cultivars of‘Chunjiangnuo 6’,‘Xiushui 121’and‘Zhejing 70’were further studied,in order to elucidate the physiological,biochemical and molecular mechanism of high vigor seed formation in conventional japonica rice.The results were as follows:1、The seed vigor of the five conventional rice varieties increased with the enhancement of maturity.After reaching the maximum value,the seed vigor decreased with the maturity.Among them,the changes of many vigor indexes of‘Chunjiangnuo 6’,‘Xiushui 121’and‘Zhejing 70’were basically consistent with the maturity,and performed best at 50 days after flowering period.However,the vigor indexes of‘Shaonuo 9714’and‘Xiushui 14’rice varieties had no obvious regularity with the maturity.2、As the maturity increased,the moisture content of fresh seeds and 1000-grain weight of five rice were varieties significantly or extremely significantly correlated with germination rate.And seed germination rate could be better predicted by establishing a quadratic equation model for water content of fresh seeds and germination rate,the regression equation was:y=-0.0996x~2+5.7395x+15.883.3、The peroxidase(POD),catalase(CAT),superoxide dismutase(SOD)and ascorbate peroxidase(APX)in the seeds of‘Chunjiangnuo 6’,‘Xiushui 121’and‘Zhejing 70’showed high activity under low temperature conditions,and the activity increased with the increase of seed vigor.The activity ofα-amylase and soluble sugar content were gradually increased with the enhancement of maturity.Furthermore,the content of proline and malondialdehyde(MDA)tended to decrease with the increase of seed vigor.4、During the development of rice seeds,the starch content increased with the enhancement of seed maturity and vigor,and the amylose content of seeds with higher vigor was also higher,however,which was decreased slightly in the conventional glutinous rice variety of‘Chunjiangnuo 6’.In addition,in the early stage of seed development,the loose spherical or elliptical starch granules gradually accelerated with the increase of seed maturity,and with the starch granules squeeze each other,the size of starch granules tended to be uniform,and the structure was dense.Gradually,the starch granules form a regular polyhedral shape with sharp edges.Besides,the back starch granules develop earlier than the abdomen.5、At 18℃,the expression of OsAmy2A,CAT3 and OsAPX2 genes in‘Zhejing 70’rice seeds were not completely consistent with the seed vigor.Among them,the expression level of OsAmy2A gene was increased with the raises of maturity,and significantly reduced after 50 days of flowering period.In the early stage of seed growth,the expression level of OsAPX2 gene in the seeds was higher,but decreased with the maturity.The expression level of CAT3 gene in seeds at the early stage of development was relatively low,and with the increase of the maturity,the expression level of CAT3gene increased significantly,and declined gradually after 50 days of flowering period.Based on the above results,in the process of conventional japonica rice breeding seed production,the seed vigor had a certain regularity with the maturity,and proper early harvesting could improve seed quality and vigor.Furthermore,the seed 1000-grain weight was not significantly reduced.Thus,it was recommended that the best harvest time of‘Chunjiangnuo 6’,‘Xiushui 121’and‘Zhejing 70’rice varieties be about 50 days after flowering.