Differences In Photosynthetic Characters Among Cowpea Varieties And The Alleviative Effect Of Exogenous EBR On NaCl Stress

Cowpea(Vigna unguiculata Linn.)is an important leguminous vegetable crop in China.The global food security issue is becoming increasingly severe,and continuously increasing crop yields is the goal pursued by agricultural production.Photosynthesis is the energy source for almost all living organisms,and improving crop photosynthesis efficiency to cultivate excellent varieties is a key way to significantly increase crop yield in the future.This paper studies the photosynthetic efficiency of different cowpea varieties to carry out genetic variation analysis in order to comprehensively evaluate cowpea variety resources,screen cowpea varieties with high photosynthetic efficiency and high yield,and provide reference basis for the innovation of cowpea germplasm resources and the breeding of new varieties.In this study,53 cowpea varieties were used as materials to carry out hydroponic and field experiments.Photosynthetic parameters,fluorescence parameters,spectral parameters,photosynthetic pigments,photosynthetic enzymes and other photosynthetic traits and agronomic traits such as pod length,pod weight and yield were measured.Genetic parameters were calculated and genetic variation analysis,correlation analysis,principal component analysis and cluster analysis were carried out.The differences of photosynthetic characteristics of 53 cowpea varieties under NaCl stress were studied by 2,4-epibrassino-lide.After treatment with CK,EBR,NaCl and EBR+NaCl,photosynthetic parameters,fluorescence parameters,spectral parameters,photosynthetic pigments,photosynthetic enzymes and other photosynthetic characteristics were determined after 3 days,and correlation analysis and principal component analysis were carried out.The effects of exogenous EBR on physiological parameters such as photosynthetic parameters and antioxidant enzymes of cowpea seedlings under NaCl stress were studied using "Ejiangdou7" in category I and "Jiang Da Zi Jiang 1" in category III obtained from cluster analysis.On the 1st,3rd,6th and 9th days after treatment,the botanical characters,photosynthetic parameters and antioxidant enzymes were measured,and variance analysis and principal component analysis were performed.The following conclusions are drawn:(1)Analyzing the difference of photosynthetic traits in 53 cowpea varieties,the results of differential analysis showed that among the 23 photosynthetic traits and 9 agronomic traits,the highest coefficient of variation was 94.413%,while the lowest was 2.472%.Among them,28 traits exceeded 10%,indicating significant differences in 28 photosynthetic and agronomic traits among these 53 cowpea varieties and rich genetic diversity.The results of genetic parameter analysis showed that the generalized heritability values of 28 photosynthetic and agronomic traits were more than 90%,indicating that these traits were mainly affected by genetic factors,while the generalized heritability data of chlorophyll b,carotenoid,NPQ and leaf length at seedling stage were between 70% and 90%,indicating that these traits were largely affected by genetic factors and less affected by environment.The results of correlation analysis showed that Pn was positively correlated with Gs,Ci and Tr.The results of principal component analysis showed that 23 photosynthetic characters and 9 agronomic characters of 53 cowpea varieties could be summarized into 10 principal components,with a cumulative contribution rate of 81.322%,reflecting a total information content of 81.322%,which could better replace 23 photosynthetic characters and 9agronomic characters to evaluate cowpea.The results of cluster analysis showed that 53 cowpea varieties could be grouped into three categories.The first category cowpea varieties had the strongest photosynthetic capacity at seedling stage,the weakest photosynthetic capacity at pod stage,and the lowest yield,which could be used for seedling research;Type II cowpea varieties have the weakest photosynthetic capacity at seedling stage,moderate photosynthetic capacity at podding stage and moderate yield,which can be used for alternative planting and production;The third type of cowpea varieties have medium photosynthetic capacity at seedling stage,the strongest photosynthetic capacity at pod stage,and the highest yield,which is suitable for planting and production.(2)Study on the differences in photosynthetic characters of 53 cowpea cultivars under NaCl stress induced by exogenous EBR,the results of difference and correlation analysis showed that the 53 germplasm resources had rich genetic diversity,and there was significant correlation between various photosynthetic characters.In CK,Pn was positively correlated with Gs,Ci and Tr,positively correlated with Leaf width,negatively correlated with Fv/Fm,and negatively correlated with Chla,Chlb and Chl(a+b).Under NaCl stress,Pn was positively correlated with Gs and Tr,and negatively correlated with Ci.Under EBR treatment,Pn was significantly positively correlated with Gs,Ci,Tr,and negatively correlated with Chla,Chlb,Chl(a+b),Y(II).Under EBR treatment and NaCl stress,Pn was significantly positively correlated with Tr,Gs and CRI1.In all treatments,Pn and Tr were significantly positively correlated.Principal component analysis showed that under CK,the photosynthetic characters of cowpea varieties could be summarized into 6 principal components,with a contribution rate of 82.298%,which could better replace 19 photosynthetic characters to evaluate 53 cowpea varieties;Under NaCl stress,the photosynthetic characteristics of cowpea varieties can be summarized into 7 main components,with a cumulative contribution rate of 84.564%;In EBR treatment,the photosynthetic characteristics of cowpea varieties can be summarized into 6 main components,with a cumulative contribution rate of 83.046%;Under EBR treatment and NaCl stress,the photosynthetic characteristics of cowpea varieties can be summarized into 7 main components,with a cumulative contribution rate of 85.742%.To explore the difference of physiological response of exogenous EBR to different cowpea varieties,so as to further explore the physiological regulation function of exogenous EBR on cowpea plants under NaCl stress,and provide more theoretical support for using exogenous EBR to alleviate the damage of cowpea under salt stress.(3)Studied the effects of exogenous EBR on photosynthetic parameters and antioxidant enzymes of two typical cowpea varieties under NaCl stress,EBR treatment increased the net photosynthetic rate of cowpea leaves of "Ejiangdou 7" and "Jiang Da Zi Jiang 1",decreased the concentration of intercellular carbon dioxide,stomatal conductance,transpiration rate,and decreased the chlorophyll a,chlorophyll b,and chlorophyll a/b of cowpea leaves,EBR treatment significantly increased the activity of antioxidant enzymes(SOD,POD,CAT,APX)and decreased the content of malondialdehyde in cowpea leaves under NaCl stress,indicating that EBR can alleviate the toxic effect of NaCl stress on cowpea.