Simultaneous p-solubilizing and biocontrol activity of rhizobacteria isolated from rice rhizosphere soil

Abstract

Application of beneficial rhizobacteria as plant biofertilizers and biocontrol agents may be a promising alternative to chemical control. To perform this aim, the present work is an evaluation of three phosphate-solubilizing Aeromonas strains isolated from the rhizosphere of rice. These selected rhizobacteria were checked for quantitative assay of tricalcium phosphate (TCP) solubilization and P concentrations were between 119.56 and 165.85 mg l-1. Then, they were evalu- ated for extracellular hydrolytic enzymes production (chitinase, cellulase, amy- lase, lipase, and protease). The results showed that they were all able to hydrolyze different substrates apart from carboxymethyl cellulose. These test bacteria were checked in vitro as well for antagonism ability against six fungal phytopatho- gens, Colletotrichum acutatum, Verticillium dahliae, Phytophthora cinnamomi, Phytophthora cactorum, Botryotinia fuckheliana, and Fusarium oxysporum, and also against five phytopathogenic bacteria, Pseudomonas savastanoi, Clavibacter michiganensis, Ralstonia solanacearum, Erwinia amylovora, and Pseudomonas syringae. GT70 was the only isolate that showed antifungal effect against two fungi, V dahliae and P. cactorum. For antibacterial activities, the best inhibition was obtained in the presence of GT70 and PT29 against R. Solanacearum. Finally, these bacteria were used for rice inoculation substituting soluble P by TCP. The results demonstrated significant increases in plant length and dry matter, especially in the presence of both strains GT70 and PT29 after 30 days under controlled conditions. However, more evaluation of these isolates under field conditions is needed before recommending them as biofertilizers.