ارزيابي روابط هورمون‌هاي اكسين و سيتوكينين بر عملكرد و اجزاي عملكرد دانۀ ذرت در شرايط تنش خشكي

Evaluation of Relationship Between Auxin and Cytokinine Hormones on Yield and Yield Components of Maize under Drought Stress Condition

كاهش رشد گیاه در شرایط تنش خشكی نتیجه بر‌هم‌خوردن تعادل هورمون‌ها می‌باشد، بنابراین كاربرد خارجی تنظیم‌كننده‌های رشد می‌تواند عاملی در جهت معكوس‌كردن تنش‌های غیر‌زنده باشد. این مطالعه به‌منظور ارزیابی كاربرد هورمون‌های سیتوكینین و اكسین بر عملكرد دانه و اجزای آن در ذرت سینگل‌كراس‌704 در شرایط تنش خشكی اجرا شد. آزمایش در سه‌محیط جداگانه، شامل محیط بدون‌تنش خشكی، تنش خشكی در مرحلۀ رشد‌رویشی و تنش خشكی در مرحلۀ رشد‌زایشی انجام شد. هورمون‌های سیتوكینین در سه‌سطح (شاهد، محلول‌پاشی در مرحلۀ پنج تا شش‌برگی و هشت تا ده‌برگی) و اكسین در سه‌سطح (شاهد، محلول‌پاشی در مرحلۀ ظهور ابریشم و 15‌روز پس از ظهور ابریشم) در هر محیط در سه‌تكرار به‌صورت فاكتوریل در قالب طرح بلوك‌های كامل تصادفی در مزرعه مؤسسه تحقیقات اصلاح و تهیه نهال و بذر كرج در سال‌ زراعی 1392‌اجرا شد. بیش‌تر‌ین عملكرد دانه در محیط بدون‌تنش و مصرف هورمون اكسین در مرحلۀ ظهور ابریشم به‌ترتیب با میانگین 80/12 و 24/12‌تن در هكتار حاصل‌شد. اختلاف عملكرد دانه در شرایط تنش زایشی و بدون‌تنش معنی‌دار بود و 21/49‌درصد نسبت به‌محیط بدون‌تنش افت كرد. محلول‌پاشی هورمون سیتوكینین باعث افزایش تعداد دانه و كاهش وزن دانه شد، ولی محلول‌پاشی هورمون اكسین باعث افزایش وزن دانه و عملكرد دانه گردید. بر اساس نتایج تجزیۀ‌مركب حاصل از این آزمایش، در شرایط تنش خشكی، محلول‌پاشی هورمون‌های سیتوكینین و اكسین به‌ترتیب در مراحل هشت تا ده‌برگی و ظهور ابریشم به‌دلیل برقرای تعادل هورمونی مختل‌شده، تا حدود 20‌درصد مانع از افت عملكرد دانه در شرایط تنش زایشی شدند و به‌عنوان مراحل حساس در واكنش به‌این هورمون‌ها در شرایط تنش خشكی توصیه می‌شوند.

<strong > Introduction </strong > Drought is one of the major environmental conditions that adversely affects plant growth and crop yield. In the face of a global scarcity of water resources, water stress has already become a primary factor in limiting crop production worldwide. Drought is the major restriction in maize production. The plant growth reduction under drought stress conditions could be an outcome of altered hormonal balance and hence the exogenous application of growth regulators under stress conditions could be the possible means for reversing the effects of abiotic stress. Phytohormones such as auxine and cytokinine are known to be involved in the regulation of plant response to the adverse effects of stress conditions. Previous studies have shown that endogenous hormones are essential regulators for translocation and partitioning of photoassimilates for grain filling in cereal crops, and therefore could be involved in the regulation of grain weight and yield. <strong > Materials and Methods </strong > The experiment was carried out in three separately environments included non-drought stress environment (irrigation after soil moisture reached to 75% field capacity), drought stress in vegetative stage (irrigation after soil moisture reached to 50% field capacity in V4 to tasseling stage, but irrigation after soil moisture reached to 75% field capacity in pollination to physiological maturity stage) and drought stress in reproductive stage (irrigation after soil moisture reached to 75% field capacity in V4 to tasseling stage and irrigation after soil moisture reached to 50% field capacity in pollination to physiological maturity stage). Cytokinin hormone in three levels (control, spraying in V5 –V6 and V8-V10 stages) and auxin hormone in three levels (control, spraying in silk emergence stage and 15 days after that) were laid out as a factorial design based on randomized complete block with three replications in each environment at Seed and Plant Improvement Institute (SPII), Karaj, Iran, in 2013. Indole-3-butyric acid and N6-benzyladenin were used as auxin and cytokinin hormones, respectively. Concentration of auxine and cytokinine hormones were 10 and 50 mg per liter, respectively. Harvesting was done from 4.5 m2 at field maturity stage with 14 % grain moisture for estimating grain yield and yield components. SAS software (version 9.1) was used for statistical analysis. Traits means were compared by Duncan 's multiple range tests in 5% probably level. <strong > Results and Discussion </strong > Drought stress effect was significant (P≤0.01) for ear number per plant, row/ear, grain number per m2, 1000 kernels weight and grain yield and it wasn’t significant for kernels/row. Spraying cytokinine hormone was significant (P≤0.01) on ear number per plant, row/ear, grain number per m2 and it was also (P≤0.05) significant for 1000 kernels weight but it wasn’t significant for kernels/row and grain yield. Spraying auxine hormone was significant (P≤0.01) for1000 kernels weight and grain yield and it wasn’t significant forother yield components. The maximum yield was obtained 12.80 and 12.24 tons per hectare in non-stress environment and using auxin hormone in silk emergence stage, respectively. Grain yield was decreased 49.21% under reproductive drought stress and grain yield difference between non drought stress and vegetative drought stress was not significant. Spraying cytokinine hormone increased ear number by 10% in V8-V10 stage. The maximum row/ear was 16.16 kernels per row which was obtained by spraying cytokinine hormone in V8-V10 stage. Spraying cytokinine hormone increased grain number per m2 up to 20.75% in V8-V10 stage but it decreased 1000 kernels weight up to 13.76% in the same stage. The maximum 1000 kernels weight was 313.87 gr that was obtained by spraying auxine hormone in silk emergence stage. Spraying auxine hormone increased grain yield up to 23.38% in silk emergence stage. <strong > Conclusions </strong > Based on the results of this experiment, maize was tolerant to drought stress up to 50% field capacity in vegetative stage, but grain yield was decreased by 48.04% under drought stress condition in reproductive stage, and spraying cytokinine and auxine hormones in V8-V10 and silk emergence stages respectively, could prevent about 20% of decreasing of grain yield. Therefore, under drought stress condition, spraying cytokinine and auxin hormones in V8 –V10 and silk emergence stage can be recommended as the best time for using these hormones respectively, because they can balance hormones rate disturbs under drought stress condition.