Investigation of morphophysiological changes of barley (Hordeum vulgare L.) under drought stress in greenhouse conditions

Plants are exposed to various environmental stresses during growth and development under natural and agricultural conditions. Drought is one of the most severe abiotic stresses that greatly affects plant yield. Metabolic changes under stress cause the morphological and physiological changes in the plant which may eventually lead to reduced yield. Barley is one of the most important cereals which a large part of the human population in many parts of the world are dependent on it as a source of food and animal feed.

In order to investigate the effects of drought stress on some morphological and physiological traits in barley as one of the most important crop, this experiment was carried out in the greenhouse of the agriculture faculty, Ferdowsi University of Mashhad in 2019 in a factorial based on a randomized complete block design with three replications. Experimental factors were included: different levels of drought stress including 100% of field capacity (control or no stress), 80, 60 and 40% of field capacity and two barley cultivars containing semi-sensitive (Fajr30) and drought tolerant (Dasht). First, the seeds of both cultivars were planted in trays filled with coco peat, perlite and sand, and after two weeks, the seedlings were transferred to pots filled with garden soil. The pots were watered daily and after one month (4 to 6 leaf stage) until the end of the growing season, they were subjected to drought stress treatments. During the vegetative stage, morphological traits such as plant height (from crown to end of plant), stem diameter, number of leaves, number of tillers, leaf area and number of stomata below and above the leaf were examined using common methods. Physiological traits including proline, soluble sugars, photosynthetic pigments and antioxidant enzymes (catalase and peroxidase) were also measured. Analysis of variance was performed using JMP statistical software version 8 and the mean of treatments was compared using LSD test at the level of 5%.

The results of this experiment showed that the effect of cultivar and drought stress were significant for many of the studied traits. The highest plant height, stem diameter, number of leaves and tillers and leaf area index were observed in plants without stress (100% FC), which was significant compared to other stress level. Also, the comparison of the two cultivars showed that Dasht, as a drought tolerant cultivar, has more leaves and tillers but less leaf area and stomata than the semi-sensitive cultivar Fajr30. In other words, the tolerant cultivar produces more leaves but smaller under stress condition which finally reduces the leaf area compared to the sensitive cultivar. This can be a good solution for drought resistance through reduce evaporation from the leaf surface as well as shading. In addition, osmotic regulators such as proline and soluble sugars and the activity of antioxidant enzymes including catalase and peroxidase increased under drought stress and it was higher in tolerant cultivar. In fact, it seems that tolerant cultivar can tolerate drought stress through activating their immune system by producing osmoprotectant and increasing the activity of antioxidant enzymes.

In general, results showed that proline, soluble sugars and antioxidant enzymes play a role in the mechanism of stress tolerance and their metabolism is affected by drought stress. The results of this experiment suggest that the accumulation of these osmoprotectans and morphological changes can be part of the drought resistance mechanisms in the drought tolerant genotype of barley, which can ultimately be used in breeding programs to improve drought tolerance. In general, the results of this experiment showed that both barley cultivars responded to drought stress, but Dasht cultivar showed more tolerance in these conditions.