عنوان مقاله [English]
Environmental stresses especially drought are important and effective factors reducing plant production. Mung bean (Vigna radiata (L) Wilczek) from leguminosae family mostly grows in tropical areas and has a lower water requirement compared to other legumes. The role of mycorrhizal symbiosis to protect plants under drought conditions is considerable. The main effects of drought stress at the flowering stage are aborting flowers and eventually declining seed yield while the major effects of drought stress are on reproductive organs of plants in the pod filling stage. Therefore, effects of drought stress occurring due to lack of water are in different growth stages which can be divided into flowering and pod filling stages. The aim of this study was to improve some morphophysiological traits, nitrogen, protein, root colonization, mycorrhizal dependency and mycorrhizal growth response percentage of mung bean by Glomus mosseae and Pseudomonas fluorescence strain 169 symbiosis under different imposed moisture stress conditions.
Materials and Methods
A split plot Randomized Complete Block Design experiment with three replications was conducted in the research farm of Islamic Azad University of Miyaneh branch, Iran, during 2016. The main factors allocated to three levels of drought stress included: normal irrigation (control), stopping irrigation in flowering stage, stopping irrigation in pods formation stage. Sub-factor was considered for four treatments of inoculation including: non-inoculation (control), inoculation by G. mosseae, P. fluorescens strain169 and G. mosseae+P. fluorescens strain169. Parto variety of mung bean (Vigna radiata L. Wilczek) used in this study was provided by Seed and Plant improvement Institute, Karaj, Iran. Suspension solutions of Pseudomonas fluorescens strain169 with 108-109 live and active bacteria per ml (CFUml-1) were provided by Water and Soil Research Institute, Karaj, Iran. Glomus mosseae was obtained from Zist Fanavaraneh Turan biotech firm, which had approximately 30 live fungi per gram and was produced by culturing in host plants, used in the form of soil mixed spores and hyphae. Inoculation of seeds by Pseudomonas fluorescence strain 169 was done in the morning by mixing them in an aluminum paper. The 2% glucose solution was added to increase the number of bacteria attached to seeds, and the seeds were then allowed to be dried in shadow. In order to increase the efficiency of fungi and bacteria in sowing time, seeds were not sterilized. Based on physicochemical analysis, the soil clay and organic carbon, nitrogen, phosphorus and potassium amount in the experimental farm was 1.5%, 0.1%, 5.70 (mg.kg-1) and 301 (mg.kg-1), respectively. In this study, traits such as protein of seed (%), nitrogen of seed (%) and root colonization (%), relative water content (%) as well as mycorrhizal dependency (%) and mycorrhizal growth response (%) were measured, and the average of ten samples from each plot for plant height (cm), the number of leaves per plant, dry weight of leaves (g), dry weight of stem+pod (g), dry weight of plant (g), stem diameter (mm) and the number of branches were collected and calculated. All measured data were analyzed for simple analysis of variance using MSTAT-C software. Mean comparison was carried out by the Duncan test at 5% probability level using SPSS (Ver.16).
Results and Discussion
Results displayed significant variation among drought stress treatments for the majority of growth characteristics. Based on inoculation treatments, there were significant differences between all measured traits except the number of leaves per plant and stem diameter. Drought stress decreased the majority of morphophysiological traits. Glomus mosseae increased dry weight of leaves and dry weight of plant by 44.3% and 8.45% respectively. G.mosseae was more effective to increase growth characteristics of mung bean. According to water requirement, pods forming stage was the most sensitive growth stage. Co-inoculation of P. fluorescence strain 169+G. mosseae synergistically affected root colonization percentage and nitrogen percentage of seeds. Protein content of seeds in drought stressed condition was more than normal irrigation plots. Plants located in cutting irrigation in pods filling stage plots plus inoculated by G. mosseae+P. fluorescence 169 had the highest protein content of seed with average 16.560%.
This study indicated that major differences between G. mosseae, Pseudomonas fluorescence strain 169 and interaction of them for their ability to enhance growth characteristics of mung bean. G. mosseae and P. fluorescence strain 169 could alleviate drought stress effects through enhancing the plant height directly. Pod formation stage was identified as a susceptible growth stage of the plant under water deficit condition. In addition, stopping irrigation in pod formation stage had a high negative influence on the number of leaves and branches in plant. The majority of measured growth characteristics was positively affected by soil microbial mass. Plants inoculated by P. fluorescence 169+G.mosseae under cutting irrigation in pod filling stage had the highest root colonization by 55.3%. Synergistic effects of G. mosseae and P. fluorescens 169 increased dry weight of stem+pod, dry weight of plant, which seems to be an important finding for physiologists and soil scientists. Glomus mosseae individually improved plant height and dry weight of leaves in cooperation with other treatments.
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