Screening Of Alkali-tolerant Sorghum Varieties And The Effects Of Alkaline Stress On Sorghum Seedling

Alkaline salt（NaHCO₃）is the main saline-alkali component in inland soda saline-alkali soil,and is also one of the important abiotic stresses affecting crop growth and development.With the increasing area of saline alkali land,breeding saline alkali tolerant crop varieties and clarifying the resistance mechanism of crops are very important for the effective use of saline alkali land.Sorghum is one of the main economic crops crops in the world,with strong salt-alkali resistance,but vulnerable to alkali stress at seedling stage.In this study,65 local varieties commonly grown in northeast China were used as materials,and the three-leaf-one-heart seedlings were treated with sole alkaline salt NaHCO₃.Through variety screening and comprehensive evaluation,the alkali tolerance factor and alkali resistance ranking of sorghum were obtained.The alkali-tolerant variety Z14 and alkali-sensitive variety Z1 were selected to measure the changes of physiological and biochemical indexes.High-throughput transcriptome sequencing was conducted to analyze the expression of related genes in alkali-tolerant cultivar Z14.The results are as follows:1.Screening and comprehensive evaluation of sorghum varieties under alkali stress.65 sorghum varieties commonly grown in northeast China were used in this study,and the screening concentration of the varieties was 60m M NaHCO₃in the preliminary test.The seedlings were cultured to the single-leaf stage with 60m M NaHCO₃,and 13 indexes including plant height,root length,dry and fresh weight of leaves,dry and fresh weight of roots,relative water content,relative electrical conductivity and chlorophyll content were determined on the fifth day.Using principal component analysis to get 13 indicators cumulative variance contribution rate of 81.86%.Among them,the aboveground fresh weight,chlorophyll a,relative conductivity,chlorophyll a/b,carotenoids,and root fresh weight have a high cumulative contribution rate,which can be used as the characteristic index for the evaluation of alkali tolerance adaptability of sorghum.After cluster analysis,65 tested materials were divided into three categories,including 9 alkali-resistant varieties,38 neutral varieties and 18 alkali-sensitive varieties.Among them,Z27,Z18,Z11,Z26,Z17,Z14 and Z58 had better comprehensive characters and could be used as candidate for sorghum cultivation and breeding in northeast China.2.Determination of growth phenotypic index indexes of alkali-tolerant and alkali-sensitive sorghum varieties under NaHCO₃stress.In this study,alkali-tolerant cultivar Z14（heilong sterile maintainer no.28）and alkali-sensitive cultivar Z1（heilong sterile maintainer no.180）were used to measure the phenotypic and root indexes of sorghum seedlings at 0d,1d,3d,5d,7d,10d,and 14d under NaHCO₃treatment at 80m M concentration.Under NaHCO₃stress,the plant height,dry fresh weight and other agronomic traits of the two cultivars decreased,and the decrease of alkali-sensitive cultivars was more obvious than that of alkali-tolerant cultivars.The differences of root length,root surface area,root volume,root tip number,root node number and root crossing number of alkali sensitive cultivars increased with the increase of stress time compared with control group.The total water content of the two cultivars decreased obviously,which was correlated with the decrease of fresh weight.3.Determination of physiological indexes of alkali-tolerant and alkali-sensitive sorghum varieties under alkali stress.Under alkali stress,the contents of chlorophyll A,chlorophyll B and carotenoid decreased gradually with the increase of stress time.The SPAD value,gas exchange parameters and chlorophyll fluorescence parameters of sorghum leaves all decreased,and the decrease of alkali-sensitive Z1 was larger than that of alkali-tolerant Z14.The content of MDA,relative conductivity,superoxide anion and hydrogen peroxide in sorghum roots and leaves increased gradually with the increase of stress time,and the content of alkali-sensitive Z1 was higher than that of alkali-tolerant Z14.The contents of SOD,POD,CAT,APX proline and soluble protein in alkali-tolerant Z14 were higher than those in alkali-sensitive Z14.The results showed that alkali-tolerant cultivars had stronger scavenging ability of reactive oxygen species than alkali-sensitive cultivars.4.Transcriptome analysis of sorghum seedling leaves under NaHCO₃stress.In this study,transcriptome sequencing analysis was conducted on RNA extracted from leaves of alkali-tolerant sorghum seedlings treated with NaHCO₃for 0h,12h,24h and 72h and it was found that with∣log2FC∣≥1,the number of differentially expressed genes in SA12h vs SA0h contrast group was the largest,the number of up-regulated genes and down-regulated genes were 2619 and 2707,respectively.Among the differentially expressed genes in different contrast groups treated with NaHCO₃,it was found that the number of biological processes enriched in GO classification was the largest,the number of signal transduction mechanisms enriched in COG annotation was the largest,and metabolism was the main part of KEGG enriched pathway.Transcriptome data were used to screen some genes involved in chlorophyll metabolism,photosynthesis and physiological response,and it was found that these genes were expressed in different degrees,thus regulating the adaptability of sorghum seedlings to alkali stress.In this study,the alkali-tolerant variety screening and comprehensive evaluation of common sorghum varieties in Northeast China were carried out,and the physiological indexes of the selected alkali-tolerant and alkali-sensitive sorghum varieties were analyzed to clarify the alkali resistant phenotype of sorghum.Further,the transcriptome sequencing of alkali tolerant sorghum variety was carried out to preliminarily screen the differentially expressed genes involved in alkali stress response and their enrichment pathways.This study provides a basis for screening sorghum varieties suitable for planting in saline-alkali areas and analyzing the physiological and molecular mechanism of sorghum alkali tolerance.