The Effect of Nitrogen Fertilizer and Different Strains of Symbiosis Bacterium on Quantitative and Qualitative Traits of Guar (Cyamopsis tetragonoloba) under Various Water Regimes

Abstract Background and Objective: The present study was aimed to investigate the effects of the application of different levels of nitrogen fertilizer and inoculation of different strains of Rhizobium bacteria on morpho-physiological, biochemical, yield and yield components of guar under different levels of drought stress.   Materials and Methods: The experiment was performed as a split factorial in a Randomized Complete Block design with three replications in the 2019-2020 growing seasons. Experimental treatments included different irrigation regimes (complete irrigation, cessation of irrigation up to 50% of flowering and 50% of podding) as main plots and treatments of different levels of nitrogen fertilizer (control, 50 and 100 kg.ha-1) and inoculation of Guar seeds with different strains of Bradyrhizobium japonicum (non-inoculation, and strains of RS150 and RS153) as subplots. Traits of plant height, shoot dry weight, number of leaves per plant, number of seeds per m2, 1000-grain weight, grain yield, biological yield, chlorophyll a, b, and total chlorophyll, carotenoids, soluble sugars, grain protein and enzymatic activities of catalase and superoxide dismutase were evaluated in the present study.   Results: The obtained results indicated that the application of low irrigation resulted in reducing all traits except indices of soluble sugars and the enzymatic activities of catalase and superoxide dismutase. On the other hand, different levels of nitrogen fertilizer and Rhizobium inoculation significantly increased all studied traits. Also, it was observed that although the strain of RS150 significantly increased chlorophyll b content and enzymatic activities of catalase and superoxide dismutase than the RS153 strain, the application of RS153 strain was maximal in other traits.   Conclusion: In general, complete irrigation was required in the study area, and increasing nitrogen fertilizer levels up to 100 kg.ha-1 had no adverse effects on morphological traits, yield, and yield components of guar plants growing under drought stress. Furthermore, the application of Bradyrhizobium japonicum moderated the negative impacts of drought stress.