اثر تنش خشکی بر مولفه‌های فتوسنتزی، عملکرد و اجزای عملکرد رقم‌های یونجه گرمسیری

به منظور مطالعه اثر تنش خشکی بر خصوصیات برگی و فتوسنتزی رقم‌های یونجه گرمسیری، آزمایشی به‌صورت کرت‌های خردشده در قالب طرح بلوک‌های کامل تصادفی با سه تکرار در سال‌های 1398-1396 در مرکز تحقیقات کشاورزی صفی‌آباد دزفول اجرا شد. عامل اصلی چهار سطح آبیاری (تامین 25، 50، 75 و 100 درصد نیاز آبی) و عامل فرعی پنج رقم یونجه (بغدادی، نیکشهری، یزدی، مساسرسا و امید) بودند. پس از استقرار گیاه در سال اول، عملکرد ماده خشک و تر و صفات مرتبط با خصوصیات برگی و فتوسنتزی اندازه‌گیری و ارزیابی شدند. نتایج نشان داد که با اعمال تنش خشکی عملکرد ماده‌تر و خشک، محتوای آب نسبی برگ (rwc) و حداکثر کارایی کوانتوم فتوسیستم دو (φpsii) کاهش ولی درصد ماده خشک علوفه، نسبت وزنی برگ به ساقه، میزان نشت الکترولیت (el) و شاخص کلروفیل (spad) افزایش یافتند. رقم بغدادی، بیشترین عملکرد ماده خشک علوفه در شرایط بدون تنش (16.9 تن در هکتار) و هم‌چنین بالاترین شاخص تحمل به تنش (sti) را درکلیه سطوح تنش خشکی (با مقادیر به‌ترتیب 19.5، 12.4 و 6 در تنش ملایم، متوسط و شدید) داشت. رقم یزدی کمترین عملکرد ماده خشک علوفه در شرایط بدون تنش (9.9 تن در هکتار) را داشت اما شاخص پایداری عملکرد (ysi) بالایی در شرایط تنش ملایم (0.988) تا شدید (0.364) داشت.

Effect of Drought Stress on Photosynthetic Parameters, Yield and Yield Components of Tropical Alfalfa Genotypes

AbstractIntroductionWater resources limitation and plant stress due to water shortage is one of the important and common environmental stresses in agricultural production, including forage production in hot and dry areas. Therefore, the selection and development of droughttolerant cultivars are very important. In irrigated lands of Iran, the average of irrigation efficiency is 37% and water productivity is 0.8 kg per cubic meters, which is lower than the world average. For increasing water efficiency, maintaining the production capacity and creating sustainable agriculture, it is necessary to identify the effective factors on the reduction of irrigation water productivity and provide an appropriate solution. In arid regions such as Khuzestan province, by using both a proper irrigation program and irrigation levels below the water requirement, obtaining an acceptable yield of alfalfa could be expected. In order to achieve these objectives, determination of the irrigation water productivity of tropical alfalfa cultivars and their drought tolerance under different irrigation regimes were the main aims of this study. Materials and MethodsFor evaluating tropical alfalfa genotypes under different drought stresses, an experiment was carried out based on split plots design with three replications in Safiabad Agricultural Research Center, Dezful, Iran, during 20192020. The main factor was four levels of irrigation (25, 50, 75 and 100% of water requirement) and the second factor was five alfalfa cultivars (Baghdadi, Nikshahri, Yazdi, Mesasirsa, and Omid). In this experiments, plant characteristics including dry and wet forage yield, percentage of dry forage, leaf to stem weight ratio, chlorophyll index (SPAD), electrolyte leakage from the leaf cell membrane (EL), relative leaf water content (RWC), and Maximum quantum yield in the darkadapted conditions (ΦPSɪɪ) were determined. Results and DiscussionThe results revealed that by applying drought stress, wet and dry forage yields, RWC, and ΦPSɪɪ  decreased but the percentage of dry forage, leaf to stem weight ratio, EL, and SPAD increased. Among the studied genotypes, the Baghdadi genotype had the highest dry forage yield in all situations; nonstress conditions (16.9 t/ha), mild drought stress (15.094 t/ha), moderate drought stress (9.58 t/ha) and severe drought stress (4.664 t/ha). The Yazdi genotype had the lowest dry forage yield; 9.9, 9.7, 5.7 and 3.6 t/ha for nonstress, mild, moderate, and severe drought stresses conditions, respectively. In our experiment, the Baghdadi genotype showed a highstress tolerance index (STI) and we highly recommend planting it in the north of Khuzestan province, but the Yazdi alfalfa genotype despite low dry forage yield under both nonstress and drought stress conditions is not recommended due to low production. We suggest using Yazdi genotype in eugenic plans due to high yield stability index (YSI) under drought stress conditions and having some favorable physiological and photosynthetic parameters associated with drought stress tolerance. ConclusionIn this study, Baghdadi alfalfa cultivar was identified as a desirable cultivar in tropical regions of Iran such as Khuzestan. Yazdi alfalfa cultivar had favorable physiological and photosynthetic components. Thus, it can be used as a favorable parent in breeding programs such as synthetic alfalfa production (through the transfer of genes associated with drought stress tolerance).