Use of seaweed )Ascophyllum nodosum) extract in mitigating the negative effects of water deficit stress in chickpea by evaluating morphophysiological indicators

Seaweed (Ascophyllum nodosum) extract can play an effective role in plant growth and development due to having plenty of nutrients, plant growth regulators and helpful microorganisms can improve soil physicochemical characteristics. Seaweed extract is rich in growth hormones such as auxin, cytokinin, nutrients and widely used elements such as nitrogen, potassium, calcium, magnesium, trace elements such as iron, zinc, copper, manganese and other valuable compounds such as mineral salts, vitamins and Antioxidants have a positive and significant effect on morpho-physiological and functional characteristics of plants. In this regard, several studies have reported that the use of seaweed extract as a foliar application can increase the morphophysiological characteristics of crops. Water deficit stress is one of the most important factors limiting plant yield, the use of remedial treatments to reduce the negative effects of stress is essential and increases the strength and resistance of plants to abiotic stresses. The main purpose of this study was the effect of foliar application of Ascophilum nodosum seaweed extract in reducing the negative effects of water deficit stress on chickpea (Adel cultivar). 

In order to evaluate the effects of seaweed extract on morpho-physiological indices of chickpea (Adel cultivar) under water deficit stress, a factorial experiment based on completely randomized design was conducted in natural environment and with three replications at the Khatam Alanbia University of Behbahan. The experiment treatments consisted of four levels of seaweed extract (0, 1.5, 2.5 and 3.5%) and three levels of water deficit stress: non-stress, moderate stress and severe stress (irrigation at 25, 50 and 75 of field capacity, respectively). In this study, morphological and physiological traits such as plant height, number of leaves per plant, number of lateral branches, number of pods per plant, shoot dry weight, root dry weight, root length, photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids and Total chlorophyll), net photosynthesis, cell membrane stability and relative water content were measured. At the end of the growth period (about 50 days after planting), the aerial part was separated from the plant roots. In order to determine the dry weight of shoots and roots, the samples were dried in an oven at 72 °C for 48 hours and then their weight was determined with the AND scale model GT-300 made in Germany with an accuracy of 0.001 g. Lichtenthaller and Wellburn (1983) method was used to measure chlorophyll and carotenoids. In order to measure the amount of net-photosynthesis, a KR8700 gas exchange-measuring device made by Korea Tech Company was used. Bian and Jiang, (2008) method was used to measure the relative water content of leaves. 

The results on the simple effects of seaweed extract showed that all foliar application levels led to a significant increase in plant height, leaf number, root dry weight, net-photosynthesis rate, cell membrane stability and carotenoids content compared to the control. Seaweed extract of 2.5 and 3.5% levels led to a significant increase in root dry weight, number of leaves per plant, plant height and cell membrane stability compared to the control. Foliar application of 2.5% compared to other levels resulted in a significant increase in net-photosynthesis and carotenoids. Evaluation of simple effects of water deficit stress showed that severe stress (25% of field capacity) significantly reduced plant height, number of leaves, root dry weight, net photosynthesis, cell membrane stability and carotenoids content compared to non-stress conditions (75% of capacity) and moderate stress (50% of field capacity). The results of interaction of treatments showed that in non-stress conditions, levels of 2.5 and 3.5% of algae extract significantly increased the number of lateral branches, number of pods per plant, shoot dry weight, root length, relative water content, chlorophyll a, b and total chlorophyll content compared to the control. Under moderate stress conditions, application of 2.5% of seaweed extract significantly increased the number of lateral branches (+33%), number of pods per plant (+22%), shoot dry weight (+19%), root length (+12 %), Relative water content (+7%), chlorophyll a (+12%), chlorophyll b (+10.5%) and total chlorophyll (+11%) were compared with the control. Under severe stress conditions, 2.5% foliar application was able to increase the number of lateral branches (+30%), number of pods per plant (+27%), relative water content (+6%) and chlorophyll b content (+10%) in compare with control. 

According to the results of this study, the use of Ascophilum nodosum seaweed extract in all studied levels is recommended for chickpea in non-stress conditions, but in moderate and severe stress levels, 2.5% is recommended to improve the morpho-physiological characteristics of chickpea.