Effects Of Foliar Spraying After Heading With Exogenous Hormones On Seed Vigor Of Hybrid Rice (Oryza Sativa L.)

Seed vigor is an important characterization of seed quality.It is urgent to improve seed production technology and produce high vigor seeds,which can alleviate the contradiction between the application of light and simplified production system based on high-quality seeds and the slow improvement of seed quality and enhance the core competitiveness of modern seed industry.Field experiments were conducted with different hybrid rice cultivars including‘Zheyou 12’（‘Zhe 04A’בZhehui 414’）,‘Zheyou 18’（‘Zhe 04A’בZhehui 818’）,‘Chunyou 84’（‘Chunjiang 16A’בC84’）and‘Chunyou 927’（‘Chunjiang 16A’בC927’）.Different concentrations of GA₃,6-BA,and IAA solutions were sprayed after 14 days artificial pollination to explore the impact of exogenous hormones spraying on seed vigor,and reveal the underlying regulatory mechanism from physiological and molecular levels,meanwhile,to screen out the appropriate spraying concentrations of exogenous hormones.This will provide the theoretical basis and technical support for the high vigor seed production of hybrid rice in China.The main results are listed as follows:1.Spraying appropriate concentrations of exogenous hormones after 14 days artificial pollination significantly promoted seed vigor of hybrid rice cultivars.Under the standard germination test,spraying different concentrations of GA₃,6-BA and IAA in 2019 and 2020 increased the germination rate,germination potential,germination index and vigor index of hybrid rice seeds by2.5-11.8%,19.0-130.0%,0.6-102.0%and 0.4-34.9%respectively.Under the artificial accelerated aging test,spraying different concentrations of GA₃,6-BA and IAA in 2020 increased the germination rate,germination potential,germination index and vigor index of hybrid rice seeds by 0.4-12.4%,6.4-77.5%,1.4-18.0%and 3.0-22.3%respectively.Based on the results of 2019 and 2020,the optimum spraying concentrations of GA₃,6-BA and IAA were 2.5,50 and 2.625 mg/L respectively.2.Spraying appropriate concentration in exogenous hormones after 14 days artificial pollination significantly increased the activities of antioxidant enzymes and decreased the content of MDA in both‘Chunyou 927’and‘Zheyou 18’.The optimal concentration was basically consistent with the result of seed vigor.After spraying 2.5 mg/L GA₃,the activity of SOD was increased by 3.2-12.7%,the activity of POD was increased by 4.8-45.3%,however the content of MDA was decreased by15.4-40.0%.After spraying 50 mg/L 6-BA,the activity of SOD in seeds was increased by 4.4-12.3%,POD activity was increased by 10.3-38.3%,MDA content was decreased by 3.6-6.9%.After spraying2.625 mg/L IAA,the activities of CAT and SOD in seeds were increased by 6.4-29.0%and 7.5-15.9%,POD activity was increased by 17.8-26.7%,MDA content was decreased by 15.4-33.3%.3.Spraying exogenous hormones with appropriate concentration after 14 days artificial pollination promoted the expression of antioxidant enzyme genes in both‘Chunyou 927’and‘Zheyou18’.The Real-Time PCR results showed that exogenous hormones significantly promoted the expression of Os APX1 and Os CSD3 genes.When sprayed concentration of 2.5 mg/L GA₃,the expression of Os APX1 and Os CSD3 was increased by 55.0%and 20.9%,respectively.The expression of Os APX1 and Os CSD3 was increased by 48.5%and 52.5%after sprayed 50 mg/L 6-BA.When sprayed concentration of 2.625 mg/L IAA,the expression of Os APX1 and Os CSD3 was increased by73.7%and 41.3%,respectively.In addition,the expression levels of Os APX1 and Os CSD3 after seed germination increased by 79.2%and 80.7%,77.3%and 27.4%,respectively.In conclusion,spraying appropriate concentrations of GA₃,6-BA and IAA after 14 days of artificial assisted pollination can induce the expression of antioxidant enzyme genes Os APX1 and Os CSD3,which promote seed antioxidant enzyme activity and improve seed antioxidant capacity,reduce malondialdehyde content and finally improve seed vigor.In the production of high vigor seeds of hybrid rice,it is recommended that the optimal spraying concentrations of GA₃,6-BA and IAA are2.5,50 and 2.625 mg/L,respectively.