Preliminary Study Of The Influence Factors On Seed Vigor In Hybrid Rice Seed Production

In order to clear the formation mechanism of hybrid rice’s seed vigor, a field experiment research was conducted using hybrid rice combination such as Jinyou974(Jin23A/R974), IIyou416(II-32A/R416), Yliangyoul(Y58S/9311) and Liangyoupeijiu(Peiai64S/9311) in Dongjiang Town Zixing county and Yongan Town Liuyang county of Hunan province. The experiment initially explored the change law of water content,grain filling and vigor of hybrid rice seeds during its development process and the effects of different seed production periods, genotypes and chemical dehydration on seed vigor. The major results are as follows:1.Seed production season had a significant effect on the F1seed vigor of hybrid rice. The seeds producting experiment of Jinyou974indicated that:In9to33days after pollination, the average germination rates of Spring (85.0%) and Summer(84.4%) seed production were significantly higher than that of Autumn seed production(76.6%); the average germination index(GI) was the same as the average germination rate; average vitality index(VI) of Summer(12.3) was significantly higher than that of Spring(10.9) and Spring significantly higher than that of Autumn(6.5); there was no significant differences about the highest germination rate among Spring(92%), Summer(91%) and Autumn(92%) during the maturation of seed(9to33days after pollination); the highest germination index(GI) of Spring(39.6) and Summer(39.9) were significantly higher than that of Autumn(32.6); the highest vitality index(VI) of Spring(19.1) was significantly higher than that of Summer(15.2) and Summer significantly higher than that of Autumn(11.2). The results indicated that Spring and Summer seed production were better than Autumn seed production considering from seed germination and vigor formation.2.In the seed producing experiment of Jinyou974, the length of time when seeds were developed with germination ability varied along with different seed production periods and Spring seed production was the earliest and Autumn seed producting was the latest. After9days of pollination, seeds of Spring and Autumn seed production did not have germination ability, while the germination rate of seeds of Summer seed production had reached to60%. The time when seeds reached the highest germination rates of Spring, Summer and Autumn seed production were all at the17th day of pollination. The formation of seed vigor on the whole presented a single-peak curve and the maximum peak was earlier in Summer and Autumn seed production(about17days after pollination) and was a little later in Spring seed production(about25to27days after flowering). The seed vigor gradually decreased after the maximum peak.3.Genotypes had a significant effect on the F1seed vigor of hybrid rice.9to33days after pollination, the average germination rate of Ⅱyou416(85.3%) was significantly higher than those of Jinyou974(82.1%) and Yliangyoul(80.6%); the average germination index(GI) of Ⅱyou416(35.6) and Jinyou974(34.5) were significantly higher than that of Yliangyoul(32.1); the average vitality index(VI) of Jinyou974(12.4) and Ⅱyou416(11.8) was significantly higher than that of Yliangyou1(9.8). The9to33days after pollination, to Flseed of hybrid rice the highest germination rate of Yliangyoul(94.5%) was significantly higher those of IIyou416(91.0%) and Jinyou974(92.0%); the highest germination index(GI) of Jinyou974(44.1)was significantly higher those of IIyou416(40.1) and Yliangyoul(39.3); the highest vitality index(VI) of Jinyou974(20.8) and IIyou416(19.0) were significantly higher than that of Yliangyoul(10.6).4.The length of time when seeds were developed with germination ability were basically consistent among different hybrid rice combinations, but the numerial sizes of every traits varied among different combinations. At the9th day after pollination, the initial germination rate of Jinyou974was significantly higher than those of IIyou416and Yliangyoul; the initial germination index(GI) decreased progressively from IIyou416, Jinyou974to Yliangyoul; the initial vitality index(VI) decreased from Jinyou974, Yliangyoul to IIyou416. The formation of seed vigor presented a single-peak curve and the maximum peak of Yliangyoul was earliest (about17days after pollination) and IIyou416the latest(about27days after flowering). The seed vigor gradually decreased after the maximum peak.5.Seed vigor was affected by the seed filling. The gaining weight process of the1000-grain weight of hybrid rice seed from Liangyoupeijiu appeared " S" curve, which were presented as a basic trend of a slow earlier stage, fast middle stage and slow later stage. The germination rate, germination index(GI) and vitality index(VI) all increased rapidly during fast growth period of grain filling. Correlation analysis indicated that there were highly significant positive correlations between seed vitality index(VI) and germination rate, germination index and the accumulation of seed’s dry matter; highly significant negative correlations between seed vitality index(VI) and the seed moisture content; negative correlations between seed vitality index(VI) and the grain filling rate.6. The dehydration effects of chemical dehydration were affected by the types of reagent, spraying stage and the concentration of reagent. During the waxy stage of F1hybrid rice of Liangyoupeijiu, eight representive dehydrating agents were sprayed as treatments and the results were as follows:the seed moisture contents were all lower than the control before harvesting, but F2-4and F2-2had the best dehydrating effects and can reduce about a half; during yellow stage, F2-4and F2-2also had the best dehydrating effects, but the spraing effects were a little worse compared with the waxy stage, for example, the high concentration treatment of F2-2reduce the moisture content12.4%.There were certain differences of dehydration effects among concentrations.7.Chemical dehydrations had a significant effect on the F1seed vigor of hybrid rice Liangyoupeijiu. The types, concentrations and spraying stages of reagents had smaller effects on germination rate, but larger effects on germination index(GI) and vitality index(VI). Comprehensive tests showed that all the treatments that had good dehydration effects had a negative effect on the seed’s germination and vigor and the influence degrees enhanced along with the increase of concentrations. Among all the chemichal dehydrating agents, F2-4-2(medium concentration) of middle waxy stage, F2-2-1(low concentration) and F2-4-2(medium concentration) of middle yellow stage not only had a good dehydrating effects, but also had a smaller effects on seed germination and vigor.