Studies On The Relationship Betweenphysical Characteristicsand Seed Vigor Of The Two-lineindicahybrid Rice

Rice is one of the main food crops in China and is the basic guarantee of national food security. With the occurrence of bottleneck problem of conventional rice breeding in yield, hybrid rice is paid more and more attention and is greatly popularized. According to statistics, the yield of hybrid rice accounts for above 58% of rice total yield in China and two-line indica hybrid rice is the main type. Seed vigor is an important index to evaluate seed quality and it has always been the research focus in the field of seed science. However, there are few reports about the relationship between rice seed physical characteristics and seed vigor. Twenty samples collected each year from 2014 to2016 were used to determine seed length, seed width, seed thickness, seed projected area, seed 1000-grain weight, seed hardness, seed volume weight, seed specific gravity, water absorption rate, and indoor germination and filed emergence rates. The physical characteristics and vigor status of rice seeds were deeply analyzed. The main conclusions are showed as follows.1.Seed vigor evaluation: Combined the results of field germination rate, germination potential, salt stress germination rate, drought stress germination rate, low temperature stress germination rate, ageing germination rate, the results of ANOVA showed that high-vigor varieties in 2014 included 'Guang liang you xiang 66', 'Y liang you 2', 'Y liang you 900', 'Jing liang you hua zhan' 'Feng liang you 9'; high-vigor varieties in 2015 included 'Y liang you 6', 'Ming laing you 829','Y liang you 2','Ben liang you 9','Liang you 378'; high-vigor varieties in 2016 included 'Y liang you 2','Y liang you 916','Ming liang you 829','N liang you l','Shen liang you 865' and so on.2. Analysis of the results of seed physical characteristics determination: The results of ANOVA showed that there were significant differences of physical characteristics among different varieties each year. Combinedthe results of vigor evaluation,seeds had higher vigor when seed length was 8.3?9.5 mm,seeds had higher vigor when seed thickness was 1.8?1.9 mm,seeds had higher vigor when seed projected area was 16.6?18.3 mm2, seeds had higher vigor when seed 1000-grain.weight was 19.5?22.5 g,seeds had higher vigor when seed hardness was 7.5?8.5 kg,seeds had higher vigor when seed water absorption rate was 0.14?0.15 kg. No obvious laws were found in other physical characteristics. The results of principal component analysis showed that there were higher loadsin seed length, seed thickness, seed projection area, seed 1000-grain weight,seed volume weight, seed specific gravity in physical characteristics.3. Correlation analysis of physical characteristics and seed vigor: According to the different annual and comprehensive analysis, there were significantly negative correlations between seed length and comprehensive vigor index (except for 2015 data).Seed width and volume weight were negatively correlated with comprehensive vigor index while they reached significant levels only in comprehensive analysis. Seed thicknesss and specific gravity were negatively correlated with comprehensive vigor index whilethey reached significant levelonly in 2015. Seed projected area was negatively correlated with comprehensive vigor index while they reached significant levelonly in 2014 and comprehensive analysis. The significant negatively correlations existed between seed 1000-grain weight and comprehensive vigor index in every year. Seed hardness was positive correlation with comprehensive vigor index while they reached significant levelonly in 2016. There were significantly positive correlations between seed water absorption rate and comprehensive vigor index (except for 2016 data). The results of cluster analysis showed that varities with lower seed length, width, projected area, thickness, 1000-grain weight, volume weight, specific gravity, and higher seed hardness, water absorption rate were clustered to the same class which varieties with higher vigor were grouped to. In general, seed length, projected area, 1000-grain weight, hardness, water absorption rate had greater affects on seed vigor of two-line indica hybrid rice.The results of this paper provides scientific basis for high-vigor seed selection and precision sowing during breeding of new variety, seed production and conditioning. Lower seed length,projected area, 1000-grain weight or higher seed hardness, water absorption rate should be considered in high-vigor seed selection process.