Alleviation of fungicide-induced phytotoxicity in greengram [Vigna radiata (L.) Wilczek] using fungicide-tolerant and plant growth promoting Pseudomonas strain

Abstract

This study was designed to explore beneficial plant-associated rhizobacteria exhibiting substantial tolerance against fungicide tebuconazole vis-à-vis synthesizing plant growth regulators under fungicide stressed soils and to evaluate further these multifaceted rhizobacteria for protection and growth promotion of greengram [Vigna radiata (L.) Wilczek] plants against phytotoxicity of tebuconazole. Tebuconazole-tolerant and plant growth promoting bacterial strain PS1 was isolated from mustard (Brassica compestris) rhizosphere and identified as Pseudomonas aeruginosa following 16S rRNA gene sequencing. The P. aeruginosa strain PS1 solubilized phosphate significantly and produced indole acetic acid, siderophores, exo-polysaccharides, hydrogen cyanide and ammonia even under tebuconazole stress. Generally, tebuconazole at the recommended, two and three times the recommended field rate adversely affected the growth, symbiosis, grain yield and nutrient uptake in greengram in a concentration dependent manner. In contrast, the P. aeruginosa strain PS1 along with tebuconazole significantly, increased the growth parameters of the greengram plants. The inoculant strain PS1 increased appreciably root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, and seed yield of greengram plants at all tested concentrations of tebuconazole when compared to the uninoculated plants treated with tebuconazole. The results suggested that the P. aeruginosa strain PS1, exhibiting novel plant growth regulating physiological features, can be applied as an eco-friendly and plant growth catalyzing bio-inoculant to ameliorate the performance of greengram in fungicide stressed soils.

Keywords: Legume; Phosphate solubilization; Plant growth promoting rhizobacteria (PGPR); Pseudomonas; Tebuconazole; Toxicity.

Figure 1

Maximum tolerance levels of phosphate solubilizing strains grown in minimal salt agar medium (devoid of carbon and nitrogen sources).

Figure 2

Plant growth promoting (PGP) activities of rhizobacterial strains recovered from mustard rhizosphere. Vertical bars represent mean of three replicates ± standard errors. Set 1, Set 2, Set 3 and Set 4 represent the PGP traits of the rhizobacterial strain PS1, PS2, PS9 and PS19, respectively. Salicylic acid; DHBA = 2,3-dihydroxy benzoic acid; IAA = indole acetic acid; EPS = exo-polysaccharides.

Figure 3

Impact of the recommended, double and three times the recommended rate of tebuconazole on the P. aeruginosa strain PS1 (in terms of optical density) grown in minimal salt agar medium (devoid of carbon and nitrogen sources).