| China's rice production is in the period of transition from intensive farming to simlified and mechanized rice production.However,seed quality of hybrid rice can not meet the requirement for simlified and mechanized rice production at present.Moreover,hybrid rice high vigor seed with high germination percentage,high field seedling emergence,high seedling quality and high seed uniformity are not generally achieved in China.Field experiments were conducted at Yongan(113°37?E,28°09?N,Altitude 98 m)and Datang(113°93?E,26°08?N,Altitude 824 m),respectively,Hunan province,China from 2017 to2019.The experimental hybrid combinations were‘?you838'(‘?-32A'as female parentבR838'as male parent),‘?you416'(‘?-32A'as female parentבR416'as male parent)and‘Jiuliangyouhuazhan'(‘33S'as female parentבHuazhan'as male parent).The mechanisms underlying the high vigor formation of hybrid rice seed were revealed from the perspectives of ecological condition,physiological characteristics,and omics analysis,respectively.Moreover,the effect and the mechanism of‘3-3-3'seed production technology on seed vigor of hybrid rice were studied.Consequently,this paper was to provide theoretical basis and technical support of improvement of hybrid rice seed vigor in China.The main results were shown as follow:(1)A significant correlation was recorded between temperatures after full heading in different ecological sites and seed vigor of hybrid rice.The values for daily mean temperature,daily maximum temperature,and daily minimum temperature after full heading in Yongan were considerably higher than Datang,respectively.Germination percentage,germination energy,germination index and vigor index in Datang were 11.9%,10.3%,10.2%and 22.7%higher than Yongan,respectively.Moreover,seedling quality in Datang was significantly higher than Yongan.Seedling fresh weight,seedling dry weight,stem base width and seedling height in Datang were 13.5%,68.8%,6.5%and 10.8%higher than Yongan,respectively.Additionally,temperatures after full heading were negatively correlated with seed vigor parameters(r=-0.8917*?-0.9885**).(2)A significant correlation was recorded between seed vigor of hybrid rice and seed filling characteristics and starch accumulation.Seed filling rate and seed filling duration in Datang(high vigor seed)were 25.0%(16.7%-33.3%)lower and 26.6%(20.8%-32.3%)higher than Yongan(low vigor seed),respectively.Moreover,the values for total starch content and amylose content of high vigor seed were 2.7%and 4.2%higher than low vigor seed,respectively.The starch granules of high vigor seed were more tightly packed and compact,while those of low vigor seed exhibited large spaces between each other.Consequently,decreasing the seed filling rate and prolonging the seed filling duration through choosing seed production environment with optimal temperatures could be beneficial to high vigor formation of hybrid rice seed.(3)Significant differences were recorded in seed vigor of early-and late-pollination hybrid rice seed.Germination percentage,germination energy,germination index and vigor index of early-pollination seed were 14.5%,12.3%,18.3%and 34.2%higher than late-pollination seed,respectively.Moreover,seed vigor of early-and late-pollination seed in high vigor seed lots were higher than low vigor seed lots,respectively.Germination percentage,germination energy,germination index and vigor index of late-pollination seed in high vigor seed lots were 26.6%,26.7%,20.9%and 39.8%higher than low vigor seed lots,respectively.Consequently,seed vigor of seed lots could be improved with cultivation measures such as early pollination and flower and seed raising.(4)The high value range of vigor index of hybrid rice was lower than the high value range of germination percentage.Germination percentage and vigor index showed a trend of quadratic parabola with downward opening with the increase of days after pollination.Based on the divided range from 75%to 125%of the day of peak value,the high value ranges of germination percentage and vigor index ranged from 16 to 26 and 17 to 24 days after pollination,respectively.About 20 days(from 17 to 24 days after pollinaiton)after pollination can be recommended as optimum harvest time of hybrid rice high vigor seed.It indicated that early harvest of hybrid seed colud be beneficial to the simultaneous improvement of germination percentage and vigor index.(5)A significant correlation was recorded between seed vigor of hybrid rice and metabolites and gene expression.The number of significantly differential metabolites of seed harvested on 20 days after pollination in different seed production sites was 59,including 53down-regulated metabolites and 6 up-regulated metabolites.Moreover,the number of significantly differential genes of seed harvested on 20 days after pollination in different seed production sites was 5411,including 2542 down-regulated genes and 2869 up-regulated genes,among which 2 biological processes and 7 molecular functions were significantly enriched.Additionally,in tricarboxylic acid cycle,the malic acid,fumaric acid and iso-citric acid of high vigor seed were significantly down-regulated,respectively.In gluconeogenesis,genes namely LOC4347383,LOC4341496,LOC4340640 and LOC4337406 of high vigor seed were significantly up-regulated,respectively.(6)The‘3-3-3'seed production technology with the characteristics including suitable site,early harvest and flower and seed raising was integrated based on mechanisms of hybrid rice high seed vigor formation.Seed vigor of hybrid rice was significantly improved with the application of‘3-3-3'seed production technology,which increased the quantity of yellow seed and quality of green seed.Germination percentage and vigor index of green seed and yellow-seed percentage with the application of‘3-3-3'seed production technology was 9.5%,22.3%and 6.7%,respectively,higher than that with the application of conventional seed production technology.Consequently,the application of‘3-3-3'seed production technology increased germination percentage,germination energy,vigor index by 6.2%,7.5%and19.0%,respectively. |
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