M.A. Thesis:

EFFECT OF SALICYLIC ACID ON REDUCING THE EFFECTS OF DROUGHT STREESS ON BARLEY YIELD

This study was conducted a split plot experiment based on randomized complete block design with three replications in Sabzevar in 2017. The treatments included irrigation at two levels of drought stress (irrigation cut from booting to harvesting stage) and complete irrigation and salicylic acid spraying treatment at four levels of zero (control), two, four and six mM at stage of shoots on barley. The results showed that in both conditions of irrigation and drought stress, the highest number of spikes, number of seeds, seed yield and biological yield per m2 were obtained in two to six mM of salicylic acid, respectively, and the lowest was related to control treatment. The lowest water use efficiency was obtained under full irrigation conditions without salicylic acid and with the consumption of salicylic acid up to six mM, water use efficiency increased. In addition, salicylic acid spraying in drought stress conditions compared to full irrigation led to increase water use efficiency. In both conditions, full irrigation and irrigation cut, the highest and lowest grain yields were obtained from 6 mM salicylic acid and control treatments (without salicylic acid spraying), respectively. Under full irrigation and drought stress, spraying with 6 mM of salicylic acid increased the grain yield by 44% and 48% compared to control (without salicylic acid spraying). It seems that the effect of salicylic acid spraying in drought stress conditions was more effective than irrigation conditions in improving irrigation water treatment than irrigation treatment. Physiological efficiency of N increased with increasing salicylic acid consumption, and consumption of six milligrams of salicylic acid with ratios of 124.6 and 132.1, respectively, in both conditions of irrigation and cut irrigation, had the highest physiological N, respectively. Cut irrigation conditions increased N remobilization, also increased the physiological efficiency of N to 113.95%. On the other hand, salicylic acid reduced drought stress by increasing physiological efficiency N and N remobilization, which improved wheat grain yield under stress conditions compared to complete irrigation. Water deficit at first affecting the structure of the cell membrane, increased the permeability of the membrane relative to the ions and macromolecules and at second stage decreased the photosynthesis by decreasing the chlorophyll index, which finally reduced the yield and its components. Also, salicylic acid alleviate drought stress by reducing ion leakage, increasing proline concentration and chlorophyll index resulting to improved wheat seed yield under stress conditions compared to full irrigation.

Keywords: Biological yield, proline, grain yield, nitrogen remobilization, and solubility.