Identification And Screening Of Saline-alkali Tolerance Of Upland Cotton Varieties In Xinjiang

Cotton is the main economic crop in Xinjiang.Salt and alkali stress inhibits the germination of cotton seeds,resulting in cotton seedling shortage or death,prolonging the growth cycle and low maturity,and poor cotton yield and quality.Therefore,screening cotton varieties resistant to saline-alkali stress and exploring its resistance mechanism are of great significance to improve cotton yield in saline-alkali soil in Xinjiang.In this study,under the indoor artificial climate chamber conditions,41 main varieties in Xinjiang were used as materials,and the saline-alkali concentration was set as 365 mmol·L^-1,390 mmol·L^-1,415mmol·L^-1and 465 mmol·L^-1of the mixed saline-alkali concentration.By measuring the germination rate and physical indexes（morphological indexes,crude fat content,protein content and water content）of cotton seeds under saline-alkali stress,2 varieties with high saline-alkali tolerance,5 varieties with saline-alkali tolerance and 34 varieties with sensitive saline-alkali tolerance were selected.High saline-alkali tolerance Xinluzhong 82（L6）,Xinluzhong 68（L7）,sensitive saline-alkali Xinluzhong 42（L12）and Xinshi H12（L39）were used as materials,and the saline-alkali concentration was set as 219 mmol·L^-1and 365 mmol·L^-1of the mixed saline-alkali concentration and the control group of clear water（CK）.The changes of water absorption,water absorption rate,germination characteristics,root characteristics and storage substances in the germination process of different resistant cotton varieties under saline-alkali stress were analyzed to explore the differences in saline-alkali tolerance of cotton varieties.In the field under different natural saline-alkali conditions（high concentration,low concentration）,with high saline-alkali tolerance varieties L7;salt-tolerant varieties Jiza 708（L9）,Xinluzhong 67（L14）,Xinluzhong70（L19）;xinluzhong 37（L1）,Xinluzhong 88（L8）,Xinluzhong 56（L18）and Xinluzhong 82（L27）were used as materials.The seedling rate,agronomic traits,photosynthetic physiology and cotton yield were measured to verify the reliability of indoor screening.The main results are as follows:（1）Screening of saline-alkali tolerance of cotton seedsThe variation coefficient of morphological indexes of 41 cotton varieties ranged from 2.55%to 9.19%,and the variation coefficient of storage materials and water content ranged from 5.11%to 21.88%.With the increase of salt concentration,cotton seed germination rate decreased.The average germination rate of cotton seeds under 390 mmol·L^-1saline-alkali stress was 44.13%lower than that of 365 mmol·L^-1.The germination rate of cotton seeds at different concentrations was classified.The first type was high saline-alkali tolerant varieties L6 and L7.The second category was salt-tolerant varieties L9,Yuanmian 11（L10）,L14,L19 and Fuquan 668（L30）;the varieties were classified into the third type of sensitive saline-alkali varieties.The saline-alkali germination rate was significantly negatively correlated with the area,diameter,length,length/width and perimeter of cotton seeds,significantly negatively correlated with the width of cotton seeds,and significantly positively correlated with roundness and protein.The area of cotton seed was significantly positively correlated with length,width,diameter and circumference,and significantly negatively correlated with roundness,protein content and crude protein content.The germination rate of regression model was 50.19-23.75×length+223.81×roundness.Therefore,through the analysis of physical indexes of cotton seeds,the rapid prediction and screening of salt and alkali resistance of cotton seeds can be realized.（2）Physiological mechanism of salt and alkali tolerance difference of different cotton varieties at germination stageWith the increase of saline-alkali concentration,the water absorption of salt-tolerant and salt-sensitive cotton varieties at germination stage under 365 mmol·L^-1mixed saline-alkali stress decreased by 18.00%and 48.05%compared with that of water.Under 219 mmol·L^-1mixed saline-alkali stress,the germination rate,germination potential and germination index of salt-tolerant and salt-sensitive cotton varieties decreased by 4.02%,14.66%,4.29%,20.00%,46.67%and 60.04%,respectively,while the average germination time increased by 7.49%and 7.23%,respectively.Under saline-alkali stress,the root length,surface addition,diameter and volume of alkali-tolerant and alkali-sensitive cotton decreased by 76.0%,152.0%,96.6%,27.9%,17.3%,108.0%,307.2%and 101.2%,respectively.Under saline-alkali stress,the total sugar,total protein and crude fat of salt-tolerant varieties were 46.90%,32.15 and 18.48%higher than those of sensitive varieties.Therefore,under saline-alkali stress,salt-tolerant cotton seeds maintained normal osmotic adjustment and enhanced salt-alkali resistance by increasing water absorption rate and storage substance content.（3）Changes in plant morphology and yield of different cotton varieties under saline-alkali conditionsSaline-alkali stress seriously inhibited the cotton seedling rate,and the seedling rate of high concentration was 75.25%lower than that of low concentration.At the early flowering stage and full boll stage,the morphological indexes（plant height,stem diameter,and number of fruit branches）of cotton under high concentration of saline-alkali decreased by 26.91%,10.19%,8.23%,16.29%,3.53%,and 7.23%compared with those under low concentration.The transpiration rate（Pn）,net photosynthetic rate（Tr）,intercellular CO₂concentration（Ci）and stomatal conductance（Gs）of cotton leaves under high concentration treatment were 3.34%,43.10%,7.52%and 36.85%lower than those under low concentration treatment on average.Compared with the low concentration treatment,the average yield per plant of cotton under high concentration saline-alkali stress was 12.60%and 13.52%lower.The yield per plant of L18 was reduced by 21%,and that of L19 was only 6%.Therefore,under saline-alkali stress,cotton varieties with strong saline-alkali tolerance can increase cotton yield by enhancing photosynthesis.In summary,according to the correlation between the germination rate of cotton seeds and the physical indexes of cotton seeds,the germination rate of cotton seeds under saline-alkali conditions was obtained by stepwise regression equation=50.19-23.75×length+223.81×roundness.High saline-alkali tolerance varieties L6 and L7 were screened.The results of indoor saline-alkali stress test showed that with the increase of saline-alkali stress,the soluble protein decomposition rate of high-tolerant varieties was faster than that of sensitive varieties under saline-alkali stress,so as to reduce the osmotic potential of cotton seeds,promote the absorption of water by cotton seeds,and reduce the damage degree of saline-alkali stress.Under natural saline-alkali stress,photosynthesis of cotton with different saline-alkali tolerance decreased,cell osmotic pressure increased,and organic matter synthesis was hindered,resulting in significant differences in yield.In this study,the external morphology of cotton seeds was associated with the germination rate of cotton seeds under saline-alkali stress,and the screening and prediction of saline-alkali tolerance were carried out.Cotton seeds with different tolerance were planted in saline-alkali areas in Xinjiang.The accuracy and reliability of rapid screening of cotton seeds were ensured by experiments,which provided a theoretical basis for high-yield planting of cotton in saline-alkali land in Xinjiang.