بررسی اثر تنش‌های خشکی و شوری بر شاخص سطح برگ، برخی صفات فیزیولوژیکی و بهره‌وری مصرف آب کنجد در منطقه گرم و خشک استان یزد

خشکی و شوری از مهم‌ترین چالش های کشاورزی در مناطق خشک و نیمه‌خشک هستند. هدف از پژوهش حاضر، بررسی شاخص سطح برگ، برخی صفات فیزیولوژیکی و بهره وری مصرف آب کنجد رقم اولتان در شرایط تنش های هم‌زمان خشکی و شوری بود. برای این منظور آزمایشی در مزرعه تحقیقاتی دانشگاه اردکان در سال زراعی 1398-1399 به صورت آزمایش فاکتوریل در قالب طرح بلوک های کامل تصادفی و با سه تکرار انجام شد. تیمارهای آزمایش شامل سه سطح آبیاری با دورهای 4، 8 و 12 روز و چهار سطح شوری آب شامل 1.5، 4، 7 و 10 دسی زیمنس بر متر بود. نتایج نشان داد که افزایش دور آبیاری از 4 به 12 روز باعث کاهش حداکثر شاخص سطح برگ به میزان 49 درصد، افزایش 14 درصدی شاخص سبزینگی و کاهش 15 درصدی پتانسیل آب برگ شد و اثر معنی دار بر دمای سطح برگ نداشت. افزایش شوری از 1.5 به 10، کاهش 58 درصدی حداکثر شاخص سطح برگ، افزایش 18 درصدی دمای سطح برگ، کاهش 40 درصدی شاخص سبزینگی و کاهش 17 درصدی پتانسیل آب را به دنبال داشت. افزایش شوری آب آبیاری از 1.5 به 4، 7 و 10، باعث کاهش 35، 80 و 96 درصدی عملکرد دانه شد. افزایش دور آبیاری از 4 به 8 و 12 روز، به ترتیب باعث کاهش معنی دار 55 و 51 درصدی بهره وری مصرف آب شد. نتایج اثر متقابل نیز نشان داد که در همه صفات مورد بررسی به‌جز پتانسیل آب برگ اختلاف معنی داری بین دورهای آبیاری 8 و 12 روز در همه سطوح شوری مشاهده نشد. اگرچه بیشترین عملکرد دانه و بهره وری مصرف آب در تیمار شوری 1.5 و دور 4 روز مشاهده شد اما بر اساس نتایج بررسی صفات فیزیولوژیکی، عملکرد دانه و بهره وری مصرف آب کنجد به خصوص در شرایط کمبود آب استفاده از دور آبیاری 12 روز به‌جای دور 8 روز در همه سطوح شوری قابل توصیه است.

investigation of drought and salinity stresses on leaf area index, some physiological traits, and water productivity of sesame in hot and arid region of yazd province

introduction:  in the irrigated agriculture of iran, the quantitative and qualitative limitations of water resources and consequently, drought and salinity stresses, always threaten crop production. this problem exists in most regions of the country. sesame is one of the oilseed and industrial crops that is somewhat resistant to drought and salinity and its placement in the cultivation pattern can provide some part of the country’s need for sesame production and oilseed crops. sesame is known as the queen of oil seeds because of its high percentage and quality of oil and high properties for health. the aim of this study was to investigate the water productivity, leaf area index, and some physiological traits of sesame oltan variety including canopy cover temperature, chlorophyll index, and water potential under simultaneous drought and salinity stresses. materials and methods:  a factorial experiment in randomized complete block design was conducted in research farm of ardakan university during the 2019 to 2020 growing season with three replications. experimental factors were four salinity levels of irrigation water including 1.5, 4, 7, and 10 ds.m-1 and three drought levels with different irrigation intervals as 4, 8 and 12 days, respectively. during the growing season, leaf area index, canopy cover temperature, and chlorophyll index were measured for four times (35, 50, 65 and 85 days after sowing). leaf water potential was also measured in the mid-growing season. water productivity for grain production was also determined. statistical analysis was done using spss version 22 software and averages were compared with duncan’s test at 5% probability level. results and discussion:  results showed that the irrigation interval had a significant effect on the leaf area index, leaf water potential, grain yield, and water productivity. irrigation water salinity had a significant effect on all of the studied traits, the interaction of the drought and salinity stresses was not only significant on spad index. increasing the irrigation interval from 4 to 12 days and increasing water salinity from 1.5 to 10 ds m-1 decreased the maximum leaf area index of sesame by 49% and 58%, respectively. also, an increase in salinity from 1.5 to 10 ds.m-1 resulted in 18% increase in leaf temperature, 40% decrease in spad index, and 17% decrease in leaf water potential. the increase in drought stress also had no significant effect on leaf temperature, while it caused 14% increase in spad index and 15% decrease in leaf water potential. increasing the irrigation interval from 4 to 8 and 12-day caused a 67 and 68% significant decrease in grain yield, respectively. there was no significant difference in the grain yield of 8 and 12-day irrigation interval. increasing the water salinity from 1.5 to 4, 7, and 10 ds.m-1 decreased the grain yield by 35, 80, and 96%, respectively. increasing the irrigation interval from 4 to 8 and 12 days caused a 55 and 51% decrease in water productivity, respectively. this index decreased significantly (95%) by increasing water salinity from 1.5 to 10 ds.m-1. conclusion:  water productivity and maximum leaf area index decreased significantly by increasing water salinity and irrigation interval. an increasing trend in leaf temperature was observed with increasing salinity, which is due to the decrease in plant transpiration under exposure to salinity stress. the spad index showed a decreasing trend with the increase in salinity, while the increase in drought stress (increasing the irrigation interval) caused an increase in this index. sesame leaf water potential also decreased by increasing salinity and drought stresses. generally, results showed that leaf area index and studied physiological traits of sesame were more affected by water salinity stress than drought stress. the results of interaction also showed that in all investigated traits, except for leaf water potential, no significant difference was observed between 8 and 12-day irrigation interval at all salinity levels. in 1.5 and 4 ds.m-1 salinity levels, the difference in grain yield and water productivity were significant in 4 and 8-day irrigation interval, while there was no significant difference in 7 and 10 ds.m-1 salinity levels. although the highest grain yield and water productivity were observed in the 4-day irrigation interval and 1.5 ds m-1 salinity level treatment, based on the results of physiological traits, grain yield, and water productivity of sesame, especially under water shortage conditions, it is recommended to use 12-day irrigation interval instead of 8-day because there was no significant difference in the water productivity.