Enhancing Fusarium oxysporum tolerance in Phaseolus vulgaris: Isolation and characterization of bacterial endophytes

Abstract

Research surrounding microbial biocontrol has garnered considerable attention in the last few years due to the numerous advantages as opposed to synthetic agrochemicals. Phaseolus vulgaris is an important legume that is cultivated worldwide, especially in third-world countries. The growth and yield of this crop are often severely limited by the pathogen Fusarium oxysporum. The aim of the study is to investigate the biological control potential of six plant bacterial isolates against F. oxysporum, both in vitro and in vivo. Six bacterial endophytes were isolated from Ledebouria ovatifolia leaves (E1), Solanum dulcamara leaves (E2), Cortalaria retusa leaves (E3), Euphorbia prostrata roots (R1), Solanum nigrum roots (R2), and Helichrysum splendidum roots (R3). These isolates were characterized for any biocontrol activity they might have against F. oxysporum PPR1. Isolation, characterization, identification, and biocontrol antagonistic assays were carried out in vitro against F. oxysporum, following standard protocols. The isolates were identified using 16S rRNA gene PCR sequencing. A phylogenetic analysis indicated that the leaf isolates displayed a close relationship with Bacillus altitudinis (E1), Streptomyces bikiensis strain SBM (E2), and Pseudomonas rhodesiae (E3). Root isolates displayed a close relationship with Enterobacter kobei (R1), Enterobacter sp. (R2), and Pseudomonas sp. strain (R3). Five out of the six isolates exhibited catalase activity and zinc solubilization activity, whereas all isolates exhibited siderophore production activity. Most of the tested isolates were able to produce the extracellular hydrolytic enzymes protease and amylase. The isolates exhibiting the highest hydrolytic enzyme activities were able to significantly inhibit F. oxysporum growth in vitro. E. kobei exhibited the most promising plant growth-promoting activity, hydrolytic enzyme activity, F. oxysporum antagonism, and increased seedling growth of P. vulgaris. These results suggest that E. kobei represents a good biocontrol candidate against F. oxysporum. The ability of this bacterial isolate to colonize and its promising biological activities suggest it has enormous potential to be used as both a biopesticide and plant growth stimulator.