Abstract
A wide range of root-associated mutualistic microorganisms have been successfully applied and documented in the past for growth promotion, biofertilization, biofortification and biotic and abiotic stress amelioration in major crops. These microorganisms include nitrogen fixers, nutrient mobilizers, bio-remediators and bio-control agents. The present study aimed to demonstrate the impact of salt-tolerant compatible microbial inoculants on plant growth; Zn biofortification and yield of wheat (Triticum aestivum L.) crops grown in saline-sodic soil and insight of the mechanisms involved therein are being shared through this paper. Field experiments were conducted to evaluate the effects of Trichoderma harzianum UBSTH-501 and Bacillus amyloliquefaciens B-16 on wheat grown in saline-sodic soil at Research Farm, ICAR-Indian Institute of Seed Sciences, Kushmaur, India. The population of rhizosphere-associated microorganisms changed dramatically upon inoculation of the test microbes in the wheat rhizosphere. The co-inoculation induced a significant accumulation of proline and total soluble sugar in wheat at 30, 60, 90 and 120 days after sowing as compared to the uninoculated control. Upon quantitative estimation of organic solutes and antioxidant enzymes, these were found to have increased significantly in co-inoculated plants under salt-stressed conditions. The application of microbial inoculants enhanced the salt tolerance level significantly in wheat plants grown in saline-sodic soil. A significant increase in the uptake and translocation of potassium (K+) and calcium (Ca2+) was observed in wheat co-inoculated with the microbial inoculants, while a significant reduction in sodium (Na+) content was recorded in plants treated with both the bio-agents when compared with the respective uninoculated control plants. Results clearly indicated that significantly higher expression of TaHKT-1 and TaNHX1 in the roots enhances salt tolerance effectively by maintaining the Na+/K+ balance in the plant tissue. It was also observed that co-inoculation of the test inoculants increased the expression of ZIP transporters (2–3.5-folds) which ultimately led to increased biofortification of Zn in wheat grown in saline-sodic soil. Results suggested that co-inoculation of T. harzianum UBSTH-501 and B. amyloliquefaciens B-16 not only increased plant growth but also improved total grain yield along with a reduction in seedling mortality in the early stages of crop growth. In general, the present investigation demonstrated the feasibility of using salt-tolerant rhizosphere microbes for plant growth promotion and provides insights into plant-microbe interactions to ameliorate salt stress and increase Zn bio-fortification in wheat.
Highlights
Seven percent of the world’s total arable land (955 million ha) is affected by salt [1,2]
The results showed that B. amyloliquefaciens B-16 grew in a medium containing 5%NaCl, whereas T. harzianum UBSTH-501 grew at a salt concentration of 4.5% only (Supplementary Table S2)
B. amyloliquefaciens B-16 was found to be positive for all the traits tested and T. harzianum UBSTH-501 was positive for HCN, indole-3-acetic acid (IAA), siderophore, starch hydrolysis, protease production and P, K and Zn solubilization under in vitro assay (Supplementary Table S2)
Summary
Seven percent of the world’s total arable land (955 million ha) is affected by salt [1,2]. Salinity, being one of the major causes of loss in agricultural production in itself, has led to considerable reduction in the area of arable land magnifying the degree of reduction in agricultural production to a greater extent [5]. These soils are more prone to water-logging due to poor texture and permeability which affects crop establishment. The high pH in sodic soils decreases the availability of many plant nutrients like N, P, Ca, Mg, Fe, Cu, Zn, etc. The increased availability of Zn reduces the accumulation of Na+ ions in the plants system and thereby protects plants from salt injury and reactive oxygen species (ROS) through improved antioxidants system [19,20]
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