Stress-resilient endophytic bacteria from mung bean (Vigna radiata L.) with biocontrol and plant growth-promoting potential.

Abstract

Plant growth-promoting endophytes with combined abiotic stress tolerance and biocontrol capacity are critical for sustainable agriculture. However, the functional diversity of mung bean (Vigna radiata L.)-associated bacterial communities and potential trade-offs between stress adaptation and antagonistic activity remain poorly understood. This study characterized endophytic bacteria from seeds and roots of mung bean cultivated in Ethiopia, to identify stress-resilient strains with biocontrol and plant growth-promoting potential. Twenty-eight endophytic bacteria were isolated from seeds (n = 16) and roots (n = 12). Eight representative isolates were screened for abiotic stress tolerance, enzymatic activities, and antifungal potential. Four isolates (GMB R1, R2, S5, S6) showed robust thermotolerance (OD₆₀₀ >0.58 at 45 °C), while others exhibited reduced growth at ≥ 40 °C. GMB R2 displayed exceptional pH tolerance (OD₆₀₀ <15% reduction across pH 4-10), and strong drought osmotolerance (OD₆₀₀ = 0.91 under 40% PEG). ACC deaminase activity was detected in six isolates, and siderophore production in seven. Enzymatic profiling revealed strain-specific specialization: GMB R1 had the highest cellulase activity (index 2.5), GMB R2 highest chitinase (1.6), and GMB S5 highest protease (2.0). Dual culture assays against Aspergillus flavus showed strong antifungal activity. Molecular identification using 16S rRNA sequencing confirmed GMB R1 as Pseudomonas fluorescens, GMB R2 as Pantoea agglomerans, and GMB S5 as Serratia marcescens. Plant growth promotion assays demonstrated cross-host efficacy in wheat (Triticum aestivum L.) and rapeseed (Brassica napus L.): GMB R1 increased rapeseed radicle length by 149%, GMB R2 enhanced wheat shoot elongation and rapeseed plumule length by 127%, and GMB S5 improved wheat root dry weight by 85% and root length by 77%. Mung bean endophytes exhibit substantial functional diversity, with combined abiotic stress tolerance, enzymatic specialization, antifungal activity, and plant growth-promoting traits. The absence of trade-offs between stress adaptation and biocontrol, together with complementary activities among isolates, highlights the potential of these strains for development as multifunctional bioinoculants suitable for marginal agroecosystems.