Physiological responses of common bean (Phaseolus vulgaris L., cv. Sanry) to foliar spray of salicylic acid and biostimulant megafol under deficit irrigation stress

Introduction Deficit irrigation stress as a consequence of the progressive decrease in water availability has been a hot topic regarding food security during the last two decades (UNESCO, 2012).Growth and development of plants is influenced by reduction in turgor that result in decreased nutrient acquisition from dry soil (Luo et al, 2011). Due to the threat of climate change, there is a need to limit the use of water resources in arid and semi-arid climates. It is therefore important to find new approaches to avoid crop productivity losses in ‘limited fresh-water’ areas. Various strategies have been proposed to help crop production under drought conditions. An alternative and quick strategy to reduce negative effects of drought stress is exogenous application of organic osmolytes or plant growth regulators. Common bean (Phaseolus vulgaris L.) is considered one of the most important grains for human alimentation. Common bean is susceptible to drought stress or water deficit, which the production of this crop in many places of the world is carried out under drought stress conditions, due to insufficient water supply by rainfall and/or irrigation. Although several studies have investigated the effects of drought stress on growth and physiological parameters of common bean, no research has been carried out on the relationship between salicylic acid and biostimulants and drought tolerance of common bean. Therefore, the objective of this study was to investigate the physiological response of common bean to foliar application salicylic acid and biostimulants under water deficit condition. Materials and methods Field experiments were carried out from June to September 2015 at the Research Farm of Agriculture Faculty at the University of Zanjan, Iran. In order to study the effect of foliar application of salicylic acid (SA) and biostimulants on some physiological treats of common bean cv. Sanry under different irrigation regimes, the experiment was conducted in a split plot based on randomized complete block design with three replicates in research filed of university of Zanjan during 2015. Three different irrigation (I) regimes (100, 75 and 50% ETc) and foliar application of salicylic acid (0.5, 1 and 1.5 mM), Megafol (0.1, 0.2 and 0.3% MF) and to distilled water as control were conducted. Seeds of ‘Sanry’ cultivar were sown on 3-4 cm depth, with 15 cm spacing within row and 30 cm spacing between rows. At 3th leaf stage, foliar applications of SA and MF were weekly sprayed. All necessary management practices such as pests and weeds control were done according to recommended practices during the crop growth. Irrigation treatments were calculated based on actual evapotranspiration (ETc) rates. Three irrigation levels were (1) control or irrigation at 100% crop water requirement (I100), Deficit irrigation at 75% and at 50% of control. Foliar treatments include salicylic acid (0.5, 1 and 1.5 mM), Megafol (0.1, 0.2 and 0.3% MF) and distilled water as control were randomly applied on the sub-plots. The experiment design was a split-plot model based on a completely randomized block design (three irrigation levels, seven foliar treatments and three replications). Results and discussion In the present study, the physiological response of common bean plants was investigated after exposure to different levels of water deficit. Furthermore, evaluation of foliar applications of salicylic acid and magafol on cell membrane stability index, leaf relative water content, proline, and antioxidant enzymes activity under different levels of water deficit conditions were done in the current study. The results showed that water deficit stress reduced leaf relative water content and cell membrane stability index, and increased electrolyte leakage, proline content and catalase and peroxidase enzymes activity. Foliar application of SA and MF had significant effects on physiological traits. The highest relative water content was obtained in MF 0.2 and 0.3% treatments. The maximum electrolyte leakage and proline content was observed in 1.5 mM SA. The highest value of peroxidase enzyme activity was achieved with spray MF 0.2% under irrigation 75 ETc%. Conclusion According to the results, MF 0.2% treatment had the highest positive effect on physiological traits of common bean plant.