Effect of Drought Stress, Mycorrhiza and Bacteria on Mother Plant on Produced Seed Vigor and its Related Traits in Soybean (Glycine max cv. Kosar)

Abstract

Introduction: Soybean is a plant that has a moderate tolerance to drought stress. Drought stress is one of the most important abiotic stresses affecting soybean production by about 40%. In addition drought stress reduces seed vigor obtained from stress conditions. Positive effects of mycorrhizal fungi on the increase of dry matter and plant biomass, especially in low-irrigated conditions and in dry areas have been proven. The reason for the increase in yield of products in mycorrhizal inoculated plants is their water balance in water deficit stress conditions and as a result of the absorption of water and mineral elements. Rhizobium bacteria, carbohydrates, and other foods are catched from the phloem vessels and received energy is used to convert nitrogen to ammonium ion and eventually amino acids. Japonicum rhizobium bacterium is not naturally in Iranian soils and bacteria should be added to the soil with seeds. Materials and Methods: This experiment was carried out to determine the germination characteristics, seed vigor and its related traits in soybean Kosar cultivar grown under drought stress conditions and inoculation with mycorrhiza and bacteria with three replications during 2018. In the field experiment, drought stress including optimal irrigation (irrigation after 70 mm evaporation), moderate stress (irrigation after 110 mm evaporation) and severe drought stress (irrigation after 150 mm evaporation from class A evaporation pan), mycorrhizal fungus in three levels, without mycorrhiza, and inoculation with glomus mosseae, Glomus intraradices and Rhizobium bacterium in two levels, including no inoculation and inoculation with Rhizobium japonicum. Results: The mean comparison showed that the seeds obtained under normal irrigation, inoculation with mycorrhiza and bacteria had the highest dry weight of radicle, plumule and seedling, percentage and germination rate. Under the mentioned conditions, the lowest electrical conductivity of the seeds and the mean time of germination were obtained. Severe and moderate drought stress compared to optimum irrigation, reduced stress tolerance index, root tolerance index and stem tolerance index, seedling vigor index and seed vigor index about 42-23, 38-18, 30-18, 50-26 and 41-21) percent, respectively. Inoculation with Glomus mosseae and Glomus intraradices compared to non-inoculation with mycorhizal fungi increased the seed vigor index, radicle lentgh, plumule lentgh and seedling lentgh by 48-42, 27-26, 41-37 and 35-33 percent, respectively. Inoculation with Rhizobium japonicum compared to non-inoculation with bacterium increased radicle lentgh, plumule lentgh and seedling lentgh by 21%, 16% and 18%, respectively. The highest water percentage of seedling tissue was obtained under optimum irrigation conditions, inoculated with mycorrhizal fungi and inoculated with rhizobium bacteria. Conclusion: According to the results of this study, in all three different irrigation conditions to improve germination and increase seed vigor, the use of mycorrhiza fungi is effective especially glomus mosseae and inoculation with Rhizobium bacteria.