Screening For Drought-tolerance Soybean Germplasm Using PEG Simulated Stress And The Physiological Chemical Characteristics In Seedling Stage Of Drought Tolerance Soybean(Glycine Max(L.)Merr.)

Drought is the main factor that restricts crop yield.Soybean is sensitive to drought and the serious drought will cause about 40%loss of soybean yield.Screening drought-tolerant varieties to adapt to poor climate conditions is the main way to increase soybean yield.In this experiment,62 soybean cultivars from different provinces in China were used as materials in order to seclect drought tolerance cultivars in soybean seelding stage by PEG8000-simulated drought stress,The drought tolerance cultivars were evaluated by principal component analysis which combined wilting index in the upper ground part and root morphological index under ground part with together.The physiological and biochemical characteristics among drought-tolerant,drought-sensitive cultivars(Glycine max(L.)Merr.)and wild soybean(Glycine soja Sieb.et Zucc.)were also investigated.The main results are as follows:1.Optimizing the PEG simulated drought stress concentration in germination test:The germination test was carried out in germination boxes with 0%(control),10%,15%,20%,25%different PEG concentrations using Tianlong 1 as material.The results showed that the germination potential was 96%,82%,76%,50%and 2%respectively under different PEG concentrations(0%,10%,15%,20%,25%).More than half of soybean seeds could germinate normally except 25%PEG treatment.There were no significant germination percentage among 0%,10%,15%and 20%PEG treatment.However,the germination percentage decreased significantly until the PEG concentration was higher than 20%.Therefore,20%PEG 8000(osmotic potential-0.54 MPa)was used as a concentration to simulate droughtstress in this experiment.2.Selecting drought-tolerant soybean varieties:62 cultivated soybeans from different parts of China were used as materials to select drought-tolerance soybean varieties.20%PEG 8000(osmotic potential-0.54 MPa)simulated drought stress was accomplished by sand culture method when the first trifoliolate leaf was developed fully.The results showed that the wilting index of each soybean variety showed polymorphic distribution after 4 d PEG treatment,with the lowest of Tiefeng 31 being 2.75,while the wilting index of Fendou 93 and Pine Bean being the highest reaching 9.Further studies showed that wilting index was positively correlated with plant height and relative conductivity,but negatively correlated with dry weight,stomatal conductance and transpiration rate.Root morphological characteristics of different cultivars showed that root-shoot ratio,root length,lateral root number,root surface area and root volume were negatively correlated with wilting index and positively correlated with root volume.The drought tolerance of 62 soybean varieties was evaluated comprehensively by the principal component analysis.Tiefeng 31 was selected as a drought tolerant cultivar,Fendou 93 was a drought sensitive cultivar,which was consistent with the wilting index.3.The physiological and biochemical characteristics among drought-tolerant varieties,drought-sensitive varieties and wild soybeans:20%PEG 8000(osmotic potential-0.54 MPa)simulated drought stress was accomplished at the time of the first threetrifoliolate leaf fully developed among drought-tolerant cultivar Tiefeng 31,drought sensitive cultivar Fendou 93 and wild soybean genotype.The indexes were measured after 0 h,6 h,24 h,48 h and 72 h drought stress treatment.The results showed that drought stress induced stomatal closure,stomatal conductance and transpiration rate decrease;dry weight of shoot decrease,root length,lateral root number,root surface area and root volume increases.The above-ground dry weight of Fendou 93 decreased by 65.94%.The root length,lateral root number,root surface area and root volume of Tiefeng 31 increased by 52.47%,169.79%,30.94%and 12.42%.However,the root length,lateral root number,root surface area and root volume of Fendou 93 decreased by 54.68%,57.75%,53.09%and 51.15%,respectively.After drought stress,SOD and POD activities increased in Tiefeng 31 and wild soybean,but CAT and APX activities increased in Fendou 93.The MDA content in Tiefeng 31 and wild beans stayed stable,and increased in Fendou 93 obviously.The contents of soluble sugar and soluble protein increased,but the changes of these two substances were very small for Tiefeng 31 and wild beans,which could be said to be basically unchanged.At the same time,under drought stress,Fendou 93 accumulated a lot of proline,while Tiefeng 31 and wild soybeans did not change much.The activities of delta-OAT,ProDH and P5CS of Fendou 93 increased,and Tiefeng 31 accumulated more ProDH and P5CS before drought.With the prolongation of drought time,the activities of ProDH and P5CS decreased.The activities of delta-OAT,ProDH and P5CS of wild soybean increased first,then decreased and then increased after drought.4.Relative expression analysis of proline metabolism-related enzymes genes:The relative expression of delta-OAT,P5CS,P5CR and ProDH genes was determined by qRT-PCR.The results showed that under mild drought stress,the expression level of the delta-OAT genes in Fendou 93 and Tiefeng 31 were up-regulated,while the expression levels of the P5CS genes in wild soybeans were down-regulated,but the relative expression levels of the P5CS genes in wild soybeans did not change significantly.The activities of proline-related enzymes showed the same trend.The P5CR and ProDH genes in three varieties were down-regulated,and the ProDH base was also down-regulated,thus reducing the degradation of proline.