Bacillus species as the most promising bacterial biocontrol agents in rhizosphere and endorhiza of plants grown in rotation with each other

Abstract

In this study, a total of 550 cultivable bacterial isolates were isolated from rhizosphere and endorhiza of rice, Berseem clover, and oilseed rape grown in rotation with each other. The potential of antifungal activity of all isolates against five rice pathogenic fungi was investigated under in vitro conditions. Of 550 isolates, 139 inhibited the mycelial growth of at least one fungal rice pathogen. The results also showed that rhizosphere and endorhiza of every third plant (three studied plants) harbored the bacteria (139 isolates) with good potential for inhibiting fungal rice pathogens in vitro. Based on biochemical tests and by comparison of 16S rDNA sequences, of the superiors six endophytic and rhizosphere isolates, which showed strong inhibitory effects against the mycelial growth of all the five fungal rice pathogens (Magnaporthe oryzae, M. salvinii, Fusarium verticillioides, F. fujikuroi, and F. proliferum), were identified. Two isolates REN4 and CEN2, isolate CEN6, isolate CEN3, and two isolates REN3 and CEN5 were closely related to Bacillus mojavensis, B. amyloliquefaciens, B. subtilis, and B. cereus respectively. Strains REN4 and REN3 were obtained from rhizosphere and endorhiza of rice, while strains CEN6 and CEN2, and strains CEN5 and CEN3 were isolated from rhizosphere and endorhiza of clover and oilseed rape respectively. Therefore, it can be concluded that plants cultivated in rotation with rice and grown on the same soil harbor protective bacteria such as genus Bacillus and that may be potential reservoirs of bio-control agents for control of the rice pathogenic fungi tested in this study.