Screening Of Salt-tolerant Germplasm Resources And Genome-wide Association Study Of Salt Tolerance Genes In Rice

With the increase of soil salinization and the growth of population,the development and utilization of saline-alkali land has received increasing attention.As one of the world's major food crops,rice(Oryza Sativa)has a certain salt tolerance.Therefore,the development of excellent rice varieties resistant to salt and alkali is one of the important ways to develop and utilize saline-alkali land.In this study,193 rice germplasms from all over the country,Korea and Japan were used as materials to screen salt tolerant germplasms at germination,seedling and reproductive growth stages,the genome-wide association study(GWAS)was used to locate the chromosome regions related to salt tolerance,and to explore the physiological mechanism of salt tolerance during the reproductive growth period through the determination of physiological indicators of some control varieties,which provided theoretical basis for improving the salt tolerance mechanism of rice and establishing the salt tolerance cultivation technology system of rice.The main results were as follows:1.All rice varieties were delayed in germination under 1.2%NaCl treatment at germination stage,and the germination rate decreased at different levels.On the 8th day after salt treatment,the germination rate was stable.Therefore,the relative salt injury rate was calculated by using the relative germination rate on the 8th day,and 16 varieties with strong salt tolerance were finally screened out.2.The salt treatment was carried out with 0.8%NaCl solution at the four-leaf stage of rice seedlings.After the salt treatment,the chlorophyll content of rice seedlings decreased gradually,and the average dead leaf rate increased instead.On the 6th day after salt treatment,most salt-sensitive rice varieties died.On the 8th day after treatment,the fresh weight of seedlings under salt treatment was significantly lower than that of control.Although the relative plant height also decreased,there was no regularity.The correlation between dry weight and root-shoot ratio and other characters was low.Finally,salt tolerant varieties were screened according to chlorophyll content,average dead leaf rate,mortality rate and fresh weight.15 varieties showed high salt tolerance at seedling stage,and one of them showed salt tolerance at germination stage and seedling stage.3.The salt treatment was carried out with 0.5%NaCl solution at the booting stage of rice,and the chlorophyll content and average dead leaf rate of rice leaves were determined at 7 d,14 d and 21 d after salt treatment,and the top three leaves were sampled and dried at 14 d to determine the content of Na+ and K+.In addition,the panicle length and seed setting rate were measured after matured.Finally,19 salt-tolerant were screened out based on the above indicators,4 of which were salt-tolerant at both booting stage and germination stage,namely Xilong 1-16,Youliudao,Qisizao 3 and Zhongyu No.1,while there were no variety was salt-tolerant at both booting stage and seedling stage.4.At the germination stage,the germination rate of the 4 d and 6 d and the corresponding SNP markers were used for genome-wide association analysis,and chromosome regions significantly correlated with salt tolerance were detected on chromosomes 1 and 8.Whole genome-wide association analysis was carried out at the seedling stage with chlorophyll content and average dead leaf rate at 4 d and 6 d,and a common chromosomal region was detected on chromosomes 1,6,7 and 12.In the 6 d and 8 d mortality analysis,the same chromosomal region was detected only on chromosomes 1 and 6,but the regions detected on chromosomes 7 and 12 were duplicated with the previous two indicators.Only one comnon region on chromosome 10 was detected using 7 d and 14 a chlorophyll content and average dead leaf rate at the reproductive growth stage.5.The content of soluble sugar,proline,malondialdehyde and the activities of antioxidant enzymes(SOD,CAT,POD)as well as the content of Na and K in roots,stems and leaves of rice during reproductive growth were determined.It was found that the salt tolerance of rice was mainly related to the maintenance of soluble sugar content in leaves,the increase of proline content and the maintenance of antioxidant enzymes activities.It was also found that salt-tolerant cultivars could effectively prevent Na from being transported from root to leaf,and had stronger ability to selectively transport K+ from root to leaf.