پديد آورندگان :
ليموچي، كاوه دانشگاه آزاد اسلامي واحد تبريز - دانشكده كشاورزي , يارنيا، مهرداد دانشگاه آزاد اسلامي واحد تبريز - دانشكده كشاورزي - گروه زراعت و اصلاح نباتات , سيادت، عطا اله دانشگاه كشاورزي و منابع طبيعي رامين , رشيدي، ورهرام دانشگاه آزاد اسلامي واحد تبريز - دانشكده كشاورزي - گروه زراعت و اصلاح نباتات , گيلاني، عبدالعلي سازمان تحقيقات، آموزش و ترويج كشاورزي - مركز تحقيقات كشاورزي و منابع طبيعي استان خوزستان - بخش اصلاح و تهيه نهال و بذر
چكيده لاتين :
Introduction: Rice is one of the important crops that is grown in large areas of the globe and is the staple food for half of the world`s population (Park et al., 2014). Khuzestan province of Iran with having 53611 hectares of land under rice cultivation produces about 240503 tons of rice annually. The prevalent irrigation method for rice production in Khuzestan is conventional water-flooding, which is considered to be inefficacious and wastes huge quantities of irrigation water (Sedaghat et al., 2015). Drought stress poses a major threat to the successful production of the crops worldwide. Therefore, one of the main challenges encountered by the agricultural sector is the production of more food with less water (Tuyen and Prasad, 2008). Rice is particularly affected by water stress. The severe decrease in the available water under alternating watering regimes (at a few day’s irrigation interval) can exceed the plant tolerance, particularly at seedling establishment stage, which can have negative impacts on vital plant developmental processes, resulting in inhibited vegetative growth. (Salehifar et al., 2014). Since the climate of Khuzestan is extremely hot, this region is prone to the frequent occurrence of drought stress. Wetting and drying of soil surface at the farm through alternating irrigation methods can facilitate the exchange of gases between the soil and its surrounding atmosphere and provide the plant root with adequate oxygen. Adopting alternating irrigation management strategy can meet crop water demands under critical water conditions (Shanmugasundaram, 2015). An important benefit of employing alternating watering methods for rice production is saving water. Thus it is important to determine how agronomic and physiological traits of different aerobic rice genotypes are impacted by the limited availability of water resulting from the use of alternating irrigation methods. Materials and Methods: This study was conducted at the farm of Agricultural Research Station of Shavoor which is affiliated with Agricultural Research Center and Natural Resources of Khuzestan province for two growing seasons of 2013-2014 and 2014-2015. The study site is between latitude 31°50’ and longitude 48°28’ at an altitude of 33m above sea level. The experiment was based on split plot design using completely randomized block layout with three replications. The main plots were allocated to two alternating watering regimes i.e. irrigation with 3 days interval (considered to be the favorable condition) and irrigation with 7 days interval (considered to be the stressful condition). The sub plots were assigned to12 rice aerobic genotypes (Oryza Sativum L. namely Vandana, IR 78908-193-B-3-B, IR 81429-B-31, IR 78875-176-B-1-B, IR 79971-B-202-2-4, IR 80508-B-194-4-B, IR 80508-B-194-3-B, IR 79907-B-493-3-1, IR 81025-B-347-3, IR 81025-B-327-3, Nada, Tarum). After the land preparation, the dry seeds of each genotype were sown in rows spaced 20 cm apart using Hamadani seed drill. Watering regimes were applied when the rice genotypes were at the middle of the tillering stage. Irrigation water for plots was supplied and controlled by a pump. The height of water in each plot was allowed to reach 5 cm, after which, the irrigation was ceased. This watering pattern implemented and maintained for the all irrigation regimes throughout the rice genotypes growing cycle. The plant responses were evaluated on the basis of several growth and physiological parameters including grain yield, 1000-grain weight, percentage of half-filled and fully-filled grains under water deficit and favorable conditions. Moreover, tolerance (TOL), drought tolerance index (DTI), drought susceptibility index (DSI), drought damage index (DDI), stress susceptibility index (SSI) and the extent of yield reduction were quantified. Results & Discussion: The results revealed that there was a large variation amongst the rice genotypes in terms of their response to alternating watering regimes. The highest drought tolerance was observed with the genotypes IR 78908-193-B-3-B and IR 81429-B-31 where their DRI was 32 % more under the stress condition (the irrigation interval of 7 days) than under the favorable condition (the irrigation interval of 3 days). The greatest drought damage occurred with genotype the IR 79971- B-202-2-4. On the basis of the grain weight susceptibility index, the genotype Tarum was found to be the most sensitive to stress. The estimation of these indices based on the grain yield demonstrated that Vandana not only outperformed other genotypes under the stress conditions but its grain yield was 17.93 higher than the other genotypes under the favorable condition. This indicates that the interaction effect between Vandan genotype and water deficit on fertility rate and grain yield was greater as compared to other genotypes. Since grain maturity period, which is considered to be a dominant mechanism in genotypes for yield loss reduction, did not decline in Vandana, it can be stated that the favorable watering condition for this tolerant genotype is the irrigation interval of 7 days. The genotypes that underwent yield decline as the result of the exposure to water-limited conditions had increased energy-expenditure due to stress endurance. Since the lower values of SSI are indicative of tolerant genotypes, Vandana with a lower SSI (- 0.522) was identified as a tolerant genotype, while other genotypes (IR 78875-176-B-1-B, IR 80508-B-194-4-B, IR 80508-B-194-3-B, IR 79907-B-493-3-1, IR 81025-B-347-3, IR 81025-B-327-3, Neda and Tarum with higher SSI (about 1 or more) were more susceptible to the stress. Conclusion: Our findings showed that the genotypes with the least tolerance to water deficit were associated with the highest drought susceptibility index and the lowest drought tolerance index, which ultimately contributed to their reduced yield. However, the genotypes that exhibited the most tolerance to drought stress were associated with the highest drought tolerance and consequently were able to acclimate to the stressful condition which helped them maintain their grain yield. In this regard, the Vandana aerobic genotype not only did not experience any decline in its yield under the stress condition, but also showed a yield increase of 390.6 kg per hectare. This makes the Vandana genotype a suitable candidate for growing under water-limited conditions. The superior indices observed in Vandana can be used in long or short-term plant breeding programs to produce more adaptable cultivars. Amongst the indices used in this study, DTI was better able to detect the drought-tolerant rice genotypes.
