Salt Tolerance Evaluation?Gene Discovery And Germplasm Innovation Of Water-saving And Drought Resistant Rice Core Resources

Rice(Oryza sativa L.)is one of the most important food crops,feeding more than half of the world's population.In its production process,it is often restricted by drought and soil salinization.Drought will aggravate the degree of soil salt damage,while salt stress will inhibit water absorption,resulting in physiological drought.At present,the water-saving and drought-resistant rice has achieved good application in alleviating the shortage of water resources.Therefore,studying the salt tolerance of water-saving and drought-resistant rice and improving its resistance to salt stress is one of the important ways to increase rice yield.Salt tolerance in rice is a complex quantitative trait refferring to a large number of genes.The research on mechanisms of salt tolerance in rice and development of salt-tolerant rice are lagging behind.The evaluation of salt tolerance and learning the molecular mechanism of salt tolerance in rice can provide informative cues in developments of salt-tolerant rice varieties.In this study,salt tolerances of 360 rice germplasm?sea rice 86?water-saving and drought-resistant rice were evaluatedat the germination satge,seedling stage,and whole life history,by measuring their performance under treatments of NaCl solutions.Meanwhile,the genome-wide association analysis was applied to identify QTLs and genes of rice salt-tolerance.Key findings are listed below:1.At the germination stage,the germination potential and germination rate was decreased,the duration of germination was prolonged,the shoot length and root length were decreased.The relative salt damage raterepresents great variations under the treatment of 200 mmol/L NaCl solution.It is therefore appropriate to evaluate salt tolerance at this concentration.The averaged damage degree of all genotypes was 2.79.It indicates that rice salt tolerance at the germination stage is morderate.The damage degree of sea rice 86 was 1.The averaged damage degree of water-saving and drought-resistant rice was 3.33.2.At the seedling stage,the average survival ratio among genotypes was 28.17%.The survival ratio was ranged from 0.00 to 100.00%.The coefficient of variation was 83.40%.The averaged damage degree of all tested genotypes at the seedling stage was 4.03.It indicates rice salt tolerance at the seedling stage was generally poor.The damage degree of sea rice 86 was 1.The averaged damage degree of water-saving and drought-resistant rice was 3.67.3.Rice growth were greatly inhibited in the field irrigated with sea water,and the yield per plant was the most sensitive to salt stress.The yield index was used to determine the damage degree due to its susceptibility under salt stress.A total of 250 materials were harvested,and based on the yield per plant,the average salt damage level of the tested genotypes during the whole growth period was 3.59.The damage degree of sea rice 86 was 1.The averaged damage degree of water-saving and drought-resistant rice was 3.67.4.By evaluating salt tolerance for these 360 genotypes at the germination stage,seedling stage,and throughout its whole life hitory,we found great differences in salt tolerance at different stages.The salt tolerance at the germination stage was significantly higher than these at the seedling stage and during whole life history.Salt tolerance in japonica rice was stronger than that of indica rice at the germination stage,seedling stage,and throughout the whole life history.There was no significant difference in salt tolerance between lowland and upland rice at seedling stage.However,salt tolerances at the germination stage and throughtout the whole life hitory were higher in upland rice than those in lowland rice.The japonica-upland rice possesses highest salt tolerance in general.5.Based on the genome-wide association analysis,we detected 51 sites which were significantly associated with salt tolerance.thirteenth known salt-tolerant genes(e.g.OsHAP2 E,OsCBL8,ZFP185,OsCCD1,OsAPX2,OsP5 CR,OsMYB2,OsLEA3-2,OsRPK1,OsAHP2,OsCam1-1,and OsBIERF3 locates within these QTLs.Meanwhile,we also identified candidate genes of salt tolerance,including OsEXPA8,LOC_Os02g33490,LOC_Os03g32160,and etc.6.The water-saving and drought-resistant rice were improved by the salt-tolerance characteristics of sea rice 86,and the salt tolerance during germination and seedling stage was significantly improved.Created 43 excellent salt-tolerant materials during the germination stage,including 16 genotypes in degree-1,27 genotypes in degree-2;27 excellent salt-tolerant materials at the seedling stage,including 10 genotypes in degree-1,17 genotypes in degree-2.In summary,we identify dosens of valueable genotypes with high salt-tolerance.They can be used in Water-saving and drought-resistant rice breeding.These candidate QTLs and genes identified in can help us to learn molecular bases of salt-tolerance.