Evaluation of Symbiotic Association between Various Rhizobia, Capable of Producing Plant-Growth-Promoting Biomolecules, and Mung Bean for Sustainable Production

Abid Mahmood,Sabir Hussain,Tanvir Shahzad,Qasim Ali,Sanaullah Yasin,Hayssam M Ali,Mohamed Z M Salem,Muhammad Ibrahim,Muhammad Khalid

doi:10.3390/su132413832

Abstract

To feed the increased world population, sustainability in the production of crops is the need of the hour, and exploration of an effective symbiotic association of rhizobia with legumes may serve the purpose. A laboratory-scale experiment was conducted to evaluate the symbiotic effectiveness of twenty wild rhizobial isolates (MR1–MR20) on the growth, physiology, biochemical traits, and nodulation of mung bean to predict better crop production with higher yields. Rhizobial strain MR4 resulted in a 52% increase in shoot length and 49% increase in shoot fresh mass, while MR5 showed a 30% increase in root length, with 67% and 65% improvement in root fresh mass by MR4 and MR5, respectively, compared to uninoculated control. Total dry matter of mung bean was enhanced by 73% and 68% with strains MR4 and MR5 followed by MR1 and MR3 with 60% increase in comparison to control. Rhizobial strain MR5 produced a maximum (25 nodules) number of nodules followed by MR4, MR3, and MR1 which produced 24, 23, and 21 nodules per plant. Results related to physiological parameters showed the best performance of MR4 and MR5 compared to control among all treatments. MR4 strain helped the plants to produce the lowest values of total soluble protein (TSP) (38% less), flavonoids contents (44% less), and malondialdehyde (MDA) contents (52% less) among all treatments compared to uninoculated control plants. Total phenolics contents of mung bean plants also showed significantly variable results, with the highest value of 54.79 mg kg−1 in MR4 inoculated plants, followed by MR5 and MR1 inoculated plants, while the minimum concentration of total phenolics was recorded in uninoculated control plants of mung bean. Based on the results of growth promotion, nodulation ability, and physiological and biochemical characteristics recorded in an experimental trial conducted under gnotobiotic conditions, four rhizobial isolates (MR1, MR3, MR4, and MR5) were selected using cluster and principal component analysis. Selected strains were also tested for a variety of plant-growth-promoting molecules to develop a correlation with the results of plant-based parameters, and it was concluded that these wild rhizobial strains were effective in improving sustainable production of mung bean.

Highlights

The global increase in human population and consequences of environmental damages have been indicating that global food production may soon be insufficient to feed all of the world’s population
A growth room experiment under controlled conditions was conducted to evaluate the effect of different wild rhizobial strains on the growth, physiology, nodulation, antioxidants enzymes, and biomass of mung bean to select the best-performing rhizobial strains for further experimentation
This variation their growth promo‐. Bean growth, This variation in in their growth promotion tion be attributable to auxin, gibberellins, and flavonoid andbiomolecules other biomolecules couldcould be attributable to auxin, gibberellins, and flavonoid and other producproduction by the rhizobia

Summary

Introduction

The global increase in human population and consequences of environmental damages have been indicating that global food production may soon be insufficient to feed all of the world’s population. It is necessary to sustainably increase agricultural productivity to produce enough food to meet the needs of the world [1]. Use of plant-growth-promoting microorganisms, especially bacteria, is one of the sustainable agricultural practices which benefit the plants either as free-living cells or by endophytic and symbiotic mechanisms [2]. Rhizobia can metabolize ambient nitrogen in root nodules and convert it into plant-available nitrogenous compounds. This process reduces the application of nitrate fertilizers and results in cost saving for both the environment and the farmer [5]. Subsequent crops may enjoy the benefits of the BNF produced by the symbiosis of legume and rhizobia along with the host crop [6]

Methods

Results

Discussion

Conclusion