Effect of irrigation on physiological traits and seed yield of soybean under inoculation with mycorrhiza fungi and rhizobium bacteria

Introduction Drought is considered to be a major threat to soybean production worldwide and yet our current understanding of the effects of drought on soybean productively is largely based on studies on above-ground traits. The symbiotic interaction between soybean and rhizobia facilitates atmospheric nitrogen fixation, a process that provides essential nitrogen to support plant growth and development. Symbiotic nitrogen fixation is important for sustainable agriculture, as it sustains plant growth on nitrogen-poor soils and limits fertilizer use for crop nitrogen nutrition (kunert et al., 2016). Application of mycorrhiza and nano oxide of Zn+Fe increased grain yield by 35.9% as compared with non-mycorrhiza, non-foliar application of nano oxide under severe water limitation. It seemed that mycorrhiza and nano oxide of Zn+Fe application was usable for profitable safflower production under water limitation condition (Seyed Sharifi and Seyed Sharifi, 2017). The aim of this study was to determine the effect of different levels of drought stress in inoculation with mycorrhiza fungi and Rhizobium bacteria on physiological traits and grain yield of soybean. Materials and methods In order to investigate the effects of water deficit stress and inoculation with mycorrhiza fungi and rhizobium bacteria on physiological traits and seed yield of soybean, an experiment was conducted as a factorial split plot design based on a randomized complete block design with three replications at research farm of agricultural highschool of Urmia during 2017. The main factor was three water deficit stress levels such as optimum, moderate and severe (irrigation after 70, 110 and 150 mm evaporation from class A evaporation pan), subplots was inoculation with mycorrhiza fungi including without mycorrhiza, and inoculation with Funneliformis mosseae and Rhizophagus intraradices and rhizobium bacteria inoculation in two levels of non inoculation and inoculation with Bradyrhizobium japonicum. In this experiment, Kowsar (new cultivar of soybean) was used. Row spacing was 50 cm and plant spaces on each rows was 10 cm. Each plots contained four rows with four meter long. To determine the seed yield, two border rows and 0.5 m from both sides of middle rows were excluded. For yield components, 10 plants were randomly collected and traits of leaf temperature, relative water content, chlorophyll a., chlorophyll b, proline, electrolyte leakage and seed yield were determined. Results and discussions By increasing water deficit stress without inoculation with mycorrhiza increased leaf temperature but decreased relative water content and chlorophyll b. By increasing water deficit stress without inoculation with bacteria leaf temperature was increased but chlorophyll b and seed yield was decreased. Inoculation with bacteria with or without inoculation with mycorrhiza decreased leaf temperature. This conditions was existed for relative water content, chlorophyll a and b content. Inoculation with bacteria and mycorrhiza specially F. Mosseae caused that maximum seed yield was obtained with 443.2 g m-2. Proline and electrolyte leakage in treatment of severe water deficit stress and non inoculation with mycorrhiza and bacteria was greater than other treatments. Minimum proline and electrolyte leakage observed in treatment of optimum irrigation and inoculation with bacteria and mycorrhiza F. mosseae. Conclusion In addition, water deficit stress caused unsuitable conditions for soybean that led to loses of seed yield but inoculation with bacteria and mycorrhiza reduced unsuitable conditions and soybean growth was improved.