Isolation and identification of bacteria from rhizosphere soil and their effect on plant growth promotion and root-knot nematode disease

The root-knot nematode (RKN) severely affects plant growth and productivity. Thus, protection of plants from RKNs has become an important task, especially for increasing crop yields. The objective of this study was to screen plant growth-promoting rhizobacteria (PGPR) for the ability to control RKNs. In this study, 860 strains of bacteria were collected from rhizosphere soil and five bacteria isolates were identified with high efficacy against RKNs: Bacillus cereus (Sneb 560), B. subtilis (Sneb 815), Pseudomonas putida (Sneb 821), P. fluorescens (Sneb 825) and Serratia proteamaculans (Sneb 851). The five bacteria isolates had high larvicidal and ovicidal activity in vitro. In a novel result, Sneb 851 showed especially high potential as a biocontrol agent against Meloidogyne incognita, causing 99.17% juvenile mortality and 61.11% egg mortality. In the pot experiment, tomato seeds treated with Sneb 825 displayed significantly higher levels of growth in root and shoot compared to control plants. Meanwhile, treatment with Sneb 815, Sneb 821 and Sneb 825 exhibited higher efficacies in reducing the number of galls and juveniles in the soil. In the field experiment, application of the five bacteria isolates increased the plant biomass and showed high biocontrol efficacy against M. incognita. The lowest gall index was observed in the treatment with Sneb 815 and Sneb 825 both in 2014 and 2015. Taken together, the five PGPR isolates can be regarded as potential biocontrol agents against RKNs in the future.