ارزیابی وضعیت آبی و مراحل بحرانی آن در ژنوتیپ‌های جو (hordeum vulgare) دیم با استفاده از شاخص تنش آبی گیاه (cwsi)

تنش رطوبتی حاصل از کمبود بارندگی (تنش خشکی) و گرما (تنش گرمایی) از عمده‌ترین تنش‌های محیطی می‌باشد که بر تولید محصولات زراعی در مناطق خشک و نیمه خشک اثر منفی می‌گذارد. مطالعه به‌منظور تعیین آستانه تنش رطوبتی با استفاده از پارامترهای تنش گرمایی مرتبط با وضعیت آبی گیاه و شناسایی و معرفی لاین‌های مقاوم به این تنش‌ها انجام گرفت. آزمایش به‌صورت کرت‌های خرد شده در قالب طرح بلوک‌های کامل تصادفی در سه تکرار و در شرایط تنش آبی (دیم) و بدون تنش آبی (50 میلی‌متر آبیاری تکمیلی در زمان کاشت و 30 میلی متر در مرحله آبستن) در کرت اصلی و 15 ژنوتیپ جو در کرت‌ فرعی در دو سال زراعی (95-1394 و 97-1396) در ایستگاه تحقیقات کشاورزی دیم (مراغه) به اجرا در ‌آمد. صفات گیاهی، عملکرد، اجزای عملکرد، دمای پوشش سبز (tc) در 6 مرحله از ظهور برگ پرچم (zgs55) الی خمیری نرم (zgs85) و ndvi در 7 مرحله از ظهور اولین گره (zgs31) الی خمیری نرم (zgs85) اندازه گیری شد. با استفاده از شاخص cwsi، آستانه تنش رطوبتی برای ژنوتیپ های جو 0/75 و آستانه دمای بحرانی 24/2 درجه سانتی گراد معادل با 7/3 میلی متر بر روز تبخیر-تعرق پتانسیل (et0) و 4/99 کیلوپاسکال کمبود فشار بخار هوا (vpd) تعیین شد. حداکثر تنش رطوبتی قابل تحمل (cwsi) به عنوان مبنای توقف کامل تعرق و فتوسنتز در گیاه جو، tc و تبخیر-تعرق پتانسیل (et0) به ترتیب 1/04، 32/7 درجه سانتی گراد و 11/01 میلی متر بر روز به‌دست آمد. شروع مرحله بحرانی از 20 خرداد (261 روز از اول مهر ماه) معادل با شروع گلدهی (zgs60) بود. در نهایت ژنوتیپ های انصار،chicm/an57//albert ، sahand/c25041 و ste/antares//yea762 مقاوم به تنش و مناسب برای شرایط دیم و ژنوتیپ‌های آبیدر، sahand/c25041، قره آرپا، chicm/an57//albert و ماکویی برای شرایط آبیاری تکمیلی توصیه می شوند.

Assessment of Water Status and Its Critical Stages in Dryland Barley Genotypes (Hordeum vulgare) Using Crop Water Stress Index (CWSI)

Introduction Barley could be grown under lowinput and harsh conditions because of its wide adaptability to drought, and heat stresses. Nonetheless, the water stress leads to yield reduction when drought stress occurs during stem elongation and grain filling stages. In rainfed areas, water and heat stress occur together, specifically after anthesis, amplifying the adverse effects of water stress via disrupting water uptake of crops. In this regard, measurement of canopy temperature (Tc) by infrared thermometry is a nondestructive method that can effectively characterize the water status of plants. There is a linear relation between Tc and transpiration, which increases upon stomata closure. Since stomata is very sensitive to environmental variations and moisture reduction in the plant and it is very difficult to measure, therefore, Tc is the preferred factor to determine the crop water status. The Tc was used to calculate the practical Crop Water Stress Index (CWSI) by Idso et al. (1981) and Jackson et al. (1981). Dold et al., (2017) reported a positive significant correlation between CWSI and transpiration, daily soil water content, and plant production. Negative significant correlations between CWSI and pure photosynthesis rate, transpiration, and stomatal conductance were also reported. This study was aimed to: (i) assess the water stress effects on dryland barley genotypes using Tc, (ii) identify the upper limit for Tc affecting performance and reducing barley grain yield, (iii) determine the critical point of water stress, and (iv) apply CWSI to select the most suitable barley genotypes for both rainfed and supplemental irrigation conditions.Materials and Methods To determine the crop water stress index (CWSI) and assess water status of dryland barley genotypes, an experiment was carried out in a split plot arrangement based on randomized complete block design with 15 genotypes in three replications at the Dryland Agricultural Research Institute, Maragheh (46° 45ʹ E, and 37° 26ʹ N), Iran in the 20152018 cropping seasons. The main plots included rainfed (as stress conditions), and supplemental irrigation (two times: 50 mm irrigation in the sowing time and 30 mm irrigation in the booting stage) as nonwater stress conditions. The subplots included 15 barley genotypes (GaraArpa, 71411, Abidar, Ansar, ARMICB, ChiCm/An57//Albert, Dobrynya, Kuban06, Makooei, Redical, Sahand, Sahand/C25041, Sararood1, Ste/Antares//YEA762 and Valfajr). The barley genotypes were planted by Wintersteiger planter in sixrow plots with 8 m long and 1.20 m wide (20 cm row spacing). The sowing rate was 380 seeds per m2 based on the thousand kernel weight (TKW) of each genotype. Seeds were treated by Penconazole fungicide. The planting dates were October 4, 2015, and October 7, 2017. In each plot, two canopy temperatures (Tc) were measured using infrared thermometer Model A1 in six crop reproductive stages from the half of ear emerged above flag leaf ligule stage (GS55) to the soft dough stage (GS85). Measuring time was between 1:00 to 2:00 pm.Results and Discussion The results indicated that the upper baseline for non–transpiring of dryland barley genotypes (TcTa = 0.0008VPD + 5.89; VPD: vapor pressure deficit) was 5.9 °C (ranged from 5.5 to 6.9) which is equal to 32.4 °C green canopy and 9.0 to 11.1 mm/day evapotranspiration. Nonstressed baseline or lower baseline (TcTa = 2.4662VPD + 9.15; R2 = 0.97**) showed that CWSI threshold value was 0.75 which is equal to 24.3 °C (23.7 to 26.1 °C) Tc under supplemental irrigation and 23.3 to 24.7 °C under water stress conditions. Additionally, CWSI threshold was equal to 7.3 mm/day evapotranspiration and 5.02 kPa VPD. On the other hand, results revealed that when Tc exceeded 25 °C, biological yield, thousand kernel weight (TKW) decreased significantly, followed by grain yield in different barley genotypes. The slope of the CWSI calibration equation (TcTa = 2.4662VPD + 9.15) is often more negative in hot and dry areas, and tends to zero in cold and humid areas. Therefore, its negativity indicates the conditions of moisture stress for barley genotypes in the dryland phase. The CWSI threshold for barley genotypes growth stages happened at 248 (6th June) days from sowing time (4th – 7th October) which is equal to flowering stage (ZGS60). According to CWSI quantity, Ansar, ChiCm/An57//Albert, Sahand/C25041and Ste/Antares//YEA762 were grouped in the tolerance class under stress (dryland) conditions. However, Abidar, Sahand/C25041, GaraArpa, ChiCm/An57//Albert and Makooei were placed in the tolerance class under nonstress (supplemental irrigation) conditions.ConclusionThe CWSI could estimate the intensity of heat and water stresses in the grain filling stage for barley genotypes in cold and semiarid areas. The average of canopy temperature threshold values were 24.8 and 24.0 °C for dryland barley genotypes in supplemental irrigation and dryland conditions, respectively. In addition, these indices could be used to estimate heat and water stress tolerance levels for barley genotypes.