كاهش اثرات تنش شوري از طريق كاربرد خارجي ساليسيليك‌اسيد بر نيشكر (Saccharum officinarum L.)

Alleviation of Salinity Effects by Exogenous Applications of Salicylic Acid in Sugarcane (Saccharum officinarum L.) Seedlings

در این تحقیق اثر سالیسیلیك‌اسید ( (SAبر رشد و برخی پاسخ‌های فیزیولوژیك گیاه نیشكر (Saccharum officinarum L.) تحت تنش شوری آزمایشی به‌صورت فاكتوریل در قالب طرح كاملاً تصادفی با سه تكرار تحت شرایط گلخآن‌های در موسسه تحقیقات و آموزش توسعه نیشكر خوزستان، ایران، طی سال. زراعی 92-1391 اجرا شد. تیمار‌های آزمایشی شامل سه سطح شوری آب آبیاری (dSm-1 1 >ECW، dSm-13ECW = ، dSm-16ECW =)، و چهار غلظت SA (صفر، 5/0، یك و 5/1‌میلی‌مولار) بودند. نتایج این تحقیق نشان‌داد كه تیمار محلول‌پاشی با سالیسیلیك‌اسید با غلظت یك میلی‌مولار به‌ترتیب موجب افزایش 61/10، 05/5 ،24/8 و 98/46‌ درصدی وزن خشك كل، درصد محتوای نسبی آب برگ، محتوای كلروفیل و نسبت پتاسیم به سدیم ریشه در مقایسه با عدم كاربرد سالیسیلیك‌اسید (شاهد) شد. نسبت پتاسیم به سدیم ریشه همبستگی مثبت و معنی‌داری با وزن خشك كل (**85/0r =)، محتوای نسبی آب برگ (**67/0r =)، همبستگی منفی و معنی‌داری با سدیم ریشه (**87/0-r =)، كلر ریشه(**85/0-r =)، داشت. سالیسیلیك‌اسید در غلظت 5/1‌ میلی‌مولار نسبت به تیمار 5/0 و یك ‌میلی‌مولار تأثیر مثبت كمتری در شرایط تنش شوری داشت. نتایج بیان‌گر آن است كه كاربرد سالیسیلیك‌اسید با غلظت یك‌میلی‌مولار در لیتر در كاهش عوارض تنش شوری مؤثر بوده و در شرایط آب و خاك مشابه كاربرد آن در نیشكر به‌صورت محلول‌پاشی توصیه می‌گردد.

<strong > Introduction </strong > Abiotic stresses cause 71% reduction in crop yield around the world, from which 20% is related to salinity stress. The importance of sugarcane increases every day due to greater demand for sugar. Since sugarcane has mainly grown in arid and semi-arid regions, salinity is one of the main problems for this crop due to higher evaporation in these areas. Salicylic acid (SA) is classified as a phyto – hormone and belongs to a group of phenol compounds. Salicylic acid can improve plant tolerance to abiotic stresses. This research aimed at studying the effect of SA on the alleviating of salinity stress in sugarcane. <strong > Materials and Methods </strong > The effects of salicylic acid on the growth and some physiological responses of sugarcane (Saccharum officinarum L. cv. CP69-1062) were studied under salt stress. The experiment design was a factorial of two factors, based on a randomized completely design with three replications. The experiment was conducted in a greenhouse at the Sugarcane Research and Training Institute of Khuzestan, Iran in 2012. Treatments evaluated in this study were three levels of salt stress, including (ECW <1 dSm-1, ECW = 3 dSm-1, ECW = 6 dSm-1), and four concentrations of SA including 0, 0.5, 1 and 1.5 mM, respectively. The plants used in this experiment were produced through tissue culture technique. The data were analyzed using SAS (ver.9.5). <strong > Results and Discussion </strong > The statistical analysis showed that salinity stress above 3 dSm-1 can significantly (P ≤ 0.05) reduce plant growth and yield. This result confirmed the previous reports about low tolerance of sugarcane to salt stress. The most efficient treatment was, spraying with 1 mM SA concentration which resulted in, 10.61, 5.05, 8.24 and 46.98 % increase in total dry weight, relative water content (RWC), chlorophyll content and root K+/Na+ ratio respectively, in comparison with control treatment. The enhancement of these plant traits will improve plant growth and crop yield. Root K+/Na+ ratio showed a significant positive correlation with total dry weight (r =0.85**), RWC, (r =0.67**), and was negatively correlated with root Na+ (r =-0.87**) and root Cl-, (r =-0.85**). Thus increasing the amount of Na+ and Cl- in plant tissues, decreases the growth and yield. Results also showed the positive effect of higher K+ concentration on plant growth and plant tolerance to salinity stress. The concentration of 1.5 mM SA had less positive effect in improving salt tolerance compared to 0.5 mM and 1 mM SA. This might be due to the hormonal effect of this compound at greater levels and its negative efficacy on plant growth and development. Greater RWC with increasing K+/Na+ ratio might be due to higher osmotic adjustment in plant tissues. <strong > Conclusions </strong > This research showed that the growth and yield of sugarcane considerably reduced under salinity stress above 3 dS m-1. The results suggested that SA was useful in reducing adverse effects of salinity. Under similar soil and water conditions the application of 1 mM in form of foliar spraying can be recommended for sugarcane plants.