بررسی اثرات کائولین و اسید سالیسیلیک بر عملکرد و برخی پاسخ‌های فیزیولوژیکی زیتون تحت تنش خشکی

کمبود آب و تنش خشکی ناشی از آن یکی از مهم‌ترین عوامل محدودکننده تولید محصولات کشاورزی در مناطق گرمسیر و نیمه گرمسیر است. در این آزمایش اثر کاربرد مستقل و برهمکنش اسید سالیسیلیک و کائولین بر تحمل به تنش خشکی در زیتون در دو سال 1398 و 1399 بررسی شده است. آزمایش به صورت فاکتوریل در قالب طرح بلوک های کامل تصادفی با سه تکرار انجام شد. برای این کار درختان 14 ساله زیتون رقم ̕زرد̔ با استفاده از تیمارهای آب مقطر (شاهد)، یک میلی مولار سالیسیلیک اسید، کائولین 2/5 درصد و کاربرد ترکیبی سالیسیلیک اسید+ کائولین محلول‌پاشی شده و پس ‌از آن تحت سه رژیم آبیاری متفاوت (100، 75 و 50 درصد نیاز آبی درخت) قرار گرفتند. نتایج نشان داد که در هر دو سال انجام آزمایش، با افزایش سطح کم‌آبیاری میزان عملکرد کل به‌طور معنی‌داری کاهش (10 تا 30 درصد) یافت. کاهش سطح آبیاری منجر به افزایش نشت یونی و مالون دی آلدهید، فنل کل و پرولین شد. همچنین با کاهش سطح آبیاری محتوای آب نسبی و کلروفیل به طور معنی داری کاهش یافت. نتایج نشان داد که محلول‌پاشی درختان زیتون با سالیسیلیک اسید و کائولین سبب کاهش نشت یونی و مالون دی آلدهید شده و محتوای رطوبت نسبی، کلروفیل، فنل و عملکرد کل را نسبت به شاهد بهبود دادند. همچنین محلول‌پاشی به‌وسیله سالیسیلیک اسید سبب افزایش معنی‌دار پرولین و کربوهیدرات کل شده و تیمار کائولین تاثیر معنی‌داری بر این صفات نداشت. در بیشتر صفات مورد ارزیابی استفاده هم‌زمان از تیمارهای سالیسیلک اسید و کائولین تاثیر هم‌افزایی نداشت. بنابراین برای کاهش آثار تنش در درخت زیتون استفاده از تیمارهای سالیسیلک یا کائولین به‌صورت جداگانه توصیه می‌شود.

Evaluation of the Effects of Kaolin and Salicylic Acid on Yield and some Physiological Responses of Olives under Drought Stress

Introduction: The availability of water for irrigating crops is one of the serious challenges at present and the future of the world. Drought stress has harmful effects on plant growth and productivity, though bringing some serious changes in plant physiology and biochemistry. Drought reduces plant growth and yield by having negative effects on plants water potential, cell division, photosynthesis activity, chlorophyll content, and protein synthesis. Although olive naturally tolerates drought, studies had shown that drought undermines its growth, yield and photosynthesis. Employing some appropriate transpirationreducing approaches could induce olive tolerance towards water deficiency. In this regard, kaolin, through raising light reflection and diminishing the rate of transpiration, is able to lessen leaf temperature in the stressed plants. Salicylic acid (SA), as a strong signaling molecule in plants, regulates physiological and biochemical functions effective in defense mechanisms and also boosts biological and nonbiological factors involved in augmenting plants.. The major roles of SA in drought stressed plants are as follows: activation of antioxidant defense system, production of secondary metabolites, synthesis of osmolytes, optimization of mineral status and maintenance of proper balance between plant photosynthesis and growth. Although some information over effects of SA and kaolin individually on stressed plants is available, to the best of our knowledge, their simultaneous effects on plants under stressful conditions has not been investigated yet. Therefore, the present study was aimed to investigate different applications of SA and kaolin (i.e. individually and simultaneously) on fieldgrown olives under drought condition.Materials and Methods: This research was conducted in Dalahu Olive Research Station located in Kermanshah province. This experiment was designed as a factorial experiment in the form of a randomized complete block design with 3 replications. Factors included different foliar spraying (i.e. control, 1 mM SA, 2.5% kaolin, and a combination of them in the mentioned concentrations) and irrigation at three levels (i.e. 100, 75, and 50% of water requirement). Irrigation was performed based on threeday interval schedule according to the above method by measuring daily evapotranspiration and required volume of water by considering the plant coefficients of olives and by drip irrigation.Results and Discussion: Although olive tree is a droughttolerant plant, drought diminished its yield. The results of this study demonstrated a decrease in total yield of olive trees due to water deficit in different years. In this regard, water deficit under high temperature and low atmospheric humidity are believed to bring about a reduction in yield of droughtstressed olive. The results of this research showed that the foliar application of SA and kaolin on olive trees led to a reduction in ionic leakage and malondialdehyde (MDA) and an increase in RWC, chlorophyll content, phenol and total yield, as compared to the control. Foliar application of SA caused a significant increase in proline content and total carbohydrates, while kaolin had no significant effect on aforementioned traits. It seems that a reduction in oxidative damage and an increase in yield of olive cultivars under different irrigations manifested several defense mechanisms induced by exogenous application of SA and kaolin. In this context, kaolin was found to protect leaves and fruits from harmful ultraviolet rays and this remarkably improves the performance of droughtstressed plants by a decrease in the ambient temperature of plants in order to mitigate deleterious effects of drought such as oxidative damage, chlorophyll degradation, and lowering RWC. These results have been substantiated for different olive cultivars at different parts of the world under this condition.In the present study, SA increased chlorophyll content, RWC, proline content, carbohydrate and total phenol; as a result, the yield of SA treated plants was higher than that in control plants. Similarly, Brito et al (5) reported that applying SA on droughtstressed olive improved osmolate accumulation, photosynthesis activities, RWC and chlorophyll content. The accumulation of phenolic compounds in SAtreated plants is believed to protect plants against stressful conditions. Therefore, the role of SA and kaolin in alleviating drought in favor of enhancing plants yield represents their efficiency under such condition. In the present study, we also employed a combination of SA and kaolin and the results showed no synergistic function between them on most traits. Therefore, to reduce the effects of drought on olive tree, it is recommended to utilize SA or kaolin separately.