The role of plant growth-promoting bacteria in alleviating drought stress on pepper plants

Abstract

Plant growth-promoting bacteria (PGPB) are important microorganisms that can be used to improve plant responses against biotic and abiotic stresses. Thus, 60 bacterial strains were isolated from pepper plants cultivated in a semiarid region in southeast Ethiopia. Initial screening for drought tolerance revealed that 12 (20.0%) isolates were able to grow in the presence of 2 M NaCl (w/v), 11 (18.33%) isolates were shown thermotolerance capacity up to 65 °C and 18 (30.0%) isolates were shown maximum tolerance for polyethylene glycol concentration (15%). Moreover, 16 (26.67%) of the strains were strong biofilm producers, while 54 (90%) were EPS producers with a better production in the medium containing 10% glucose. Also, the highest flocculation yield was recorded by AAUSR23 (148 mg/L) at 0.5 M of NaCl. A subset of 10 strains was identified based on a semi-automated Biolog MicroPlate identification system and belonged to fourteen genera (Bacillus spp, Pseudomonas spp. Stenotrophomonas spp, Enterobacter spp, Achromobacter spp, Comamonas spp, Acinetobacter spp, Burkholderia spp, Serratia spp, Ocrobactrum spp, Pantoea spp, Rhizobium spp, Aeromonas spp, and Klebsiella spp). Four selected strains produce auxin on the root tip of Arabidopsis thaliana when treated with DR5::GUS. The bacterized seeds of pepper with four selected drought resistant bacterial strains were evaluated in the greenhouse; the inoculated plants showed 23.6–52.8% and 41–79.6% higher shoot and root lengths, respectively, compared with the control. Our results showed that drought resistant bacteria isolated from the rhizosphere and endophyte of pepper grown on water deficient lands might be used for alleviating drought stress in crop plants.