Effects of biochar and salicylic acid on physiological and orphological characteristics of European borage (Borago officinalis L.) under water defecit conditions

Water deficit has been the major contributor to the decline in plant yield. Soil amendment and certain hormonal agents are some strategies applied to mitigate the adverse effects of drought stress. The purpose of this study was to investigate the effects of one soil modifier and one growth regulator on some physiological and morphological characteristics of Borago officinalis L. under water deficit conditions. The experiment was implemented as a split-factorial in a randomized complete block design with four replications at the research farm of Agriculture Faculty of Shahroud University of Technology, Iran during 2017- 2018. The main plots consisted of three levels of irrigation (usual irrigation every five days, irrigation every 10 and 15 days) and sub-plots consisted of biochar at three levels (0, 5 and 10 t ha-1) and salicylic acid at two levels (0 and 0.5 mM). Based on the results, biochar, salicylic acid, and water deficit factors affected the number of flowering stems, number of stems, stem height, the amount of chlorophylls a and b, total chlorophyll, and carotenoids significantly. Interactions between salicylic acid and water deficit levels had the most effects on carotenoids and chlorophyll b. Triple interaction of factors also affected the total dry weight, number of flowering stems, the number of stems, stem height, and chlorophyll b. Generally, water deficit stress decreased the amount of photosynthetic pigments and leaf growth indices of European borage compared to control, and salicylic acid and biochar reduced the negative effects on the amount of photosynthetic pigments. Therefore, the use of biochar as a soil modifier and salicylic acid as a growth regulator seems to be useful in ameliorating some of the negative effects of water stress on Borago officinalis.