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ABSTRACT Excessive cobalt (Co) levels in agricultural soil cause significant toxicity, reducing crop growth and yield. This study aimed to assess the potential of Klebsiella sp. SRB‐5 (Accession no. OR715782), in mitigating cobalt toxicity and enhancing the growth of garden peas under cobalt stress. Strain SRB‐5, tolerant to 4000 ppm of Co(II), was evaluated for producing growth‐regulating substances, including indole‐3‐acetic acid (IAA), ammonia, siderophore, ACC deaminase, and solubilized phosphate, under cobalt stress. The optimal conditions for Co‐(II) biosorption by SRB‐5 were determined to be 25°C, pH 6.0, and an incubation time of 72 h. The strain's ability to mitigate Co‐(II) toxicity was tested by inoculating peas grown in soil treated with 1000, 2000, and 3000 ppm Co‐(II). Inoculation with Co‐tolerant SRB‐5 alleviated cobalt toxicity and significantly enhanced the physiological and biochemical properties of plants. Notably, SRB‐5 increased root length (19.2%), root biomass (29%), seedling vigor index (18.4%), total chlorophyll (52%), nodule biomass (41%), leghaemoglobin content (38%), root nitrogen (27%), and phosphorous content (19.3%) in 1000 ppm Co‐stressed peas. Additionally, bacterial inoculation reduced proline, malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ), and membrane injury by 85%, 57.3%, 90%, and 75%, respectively, in 1000 ppm Co‐exposed plants. Priming with SRB‐5 also reduced cobalt uptake in roots (88%), shoots (53.7%), and grains (79.6%) compared to uninoculated treatments. Metal‐tolerant beneficial soil bacteria, such as Klebsiella sp. strain SRB‐5, could serve as an effective alternative for enhancing pea production in metal‐contaminated soils. The use of Co‐tolerant PGPR strains holds potential for development as biofertilizers in future agricultural practices.
Danish et al. (Fri,) studied this question.