Document Type : Applicable
Authors
1 M.Sc Graduate, Department of Soil Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran.
2 Assistant Professor, Department of Soil Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran
3 Associate Professor, Department of Soil Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran
Abstract
Introduction: Abiotic stresses are the most important limiting factors affecting agricultural productivity. Soil salinity is considered one of the most severe abiotic stresses in plants. Crop plants must use biological mechanisms to cope with unfavorable environmental conditions. Their growth, development, and yield will be reduced if they fail in coping with such conditions. The plant microbiome provides plants with the main basic support they need to obtain nutrients, resist diseases, and tolerate abiotic stresses. The metabolic and genetic potential of the plant microbiome transforms plants into appropriate organisms for fighting unfavorable environmental conditions. Hence, the use of salt-tolerant halophyte rhizosphere bacteria is an effective strategy for improving plant growth in saline soils.
Materials and methods: Consequently, this research intended to isolate indigenous resistant bacteria adapted to salinity stress conditions from the rhizosphere of desert plants in Kerman Province and determine their effects on some physiological and biochemical characteristics of maize plants in soil under salt stress. First, the rhizosphere bacteria of desert trees were isolated and purified. Next, their growth was studied at various sodium chloride concentrations (0, 100, 200, 300, 400, 500, 600, and 650 mM) in solid microbial culture media and then in quantitative testing at various sodium chloride concentrations (0, 320, 650, and 850 mM) in liquid microbial culture media. Four bacterial strains (BZ79, BR90, BG59 and BG71) were selected for the greenhouse stage. The greenhouse experiment was performed on maize plants with three replications using a completely randomized design arranged as a factorial consisting of four salt-tolerant strains and a control at two soil salinity levels: non-saline soil (1.32 dS/m) and saline soil (12 dS/m). The experiment was completed in 90 days. Finally, dry weight of the aerial organs, fresh weight of the aerial organs and of the roots, length of the aerial organs and of the roots, concentrations of chlorophyll a, b, total chlorophyll, and carotenoid content of maize plants in saline and non-saline soils were measured.
Results and discussion: The results of the statistical analysis showed that the bacterial strains differed significantly in salt tolerance, and some of them were even able to tolerate high sodium chloride concentrations (up to 850 mM) and grow well. Salt stress causes osmotic stress, ionic imbalance, and oxidative damage in maize plants thereby decreasing growth and photosynthetic efficiency. The results indicated that increases in salinity level reduced dry matter of the aerial organs (51.4%), fresh weight of the aerial organs (24.4%), fresh weight of the roots (15.9%), length of the aerial organs (7.8%), chlorophyll a content (64.2%), chlorophyll b content (115%), and carotenoid content (3%). However, inoculation of the maize plants with salt-tolerant bacteria significantly increased dry weight of the maize plants, fresh weight of the aerial organs and of the roots, length of the aerial organs and of the roots, concentrations of chlorophyll a, chlorophyll b, and total chlorophyll, and carotenoid content in non-saline and saline soils. Of course, the increases in these plant parameters caused by inoculation with salt-tolerant bacteria were more pronounced in saline soil compared to non-saline soil. The results demonstrated that, compared to the uninoculated control (B0), inoculation of the plants with the bacterial strains BZ79, BR90, BG59, and BG71 increased dry weight of the aerial organs in the non-saline soil by 20%, 12.3%, 13%, and 3%, respectively, and by 62.2%, 39.5%, 59%, and 41.4%, respectively, in the saline soil. The largest dry weight of the aerial organs (25.95 g) was recorded in the maize plants inoculated with BZ79 and the smallest (1 g) in those uninoculated with the control (B0). Compared to the uninoculated control (B0), inoculation of the maize plants with BZ79, BG59, and BG71 in the saline soil improved chlorophyll a concentration by 1.7%, 1.9%, and 2.4%, respectively, and increased chlorophyll b concentration by 2.6%, 1.7%, and 1.8%, respectively. However, inoculation with BR90 did not increase chlorophyll a content. In the saline soil, inoculation with both BR90 and BG59 led to a three-fold increase in carotenoid content compared to the uninoculated control.
conclusion: Among the indigenous rhizosphere bacteria, BZ79 was the most effective in improving maize plant tolerance to salt stress. These findings indicated the potential of these indigenous salt-tolerant bacteria as an effective factor for reducing the damage caused by salt stress by increasing the physiological performance of the maize plants and the photosynthetic pigments in them. Given the beneficial effect of the indigenous salt-tolerant bacteria under saline soil conditions, these microorganisms have the potential to be candidate as biofertilizer in the future.
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