An in planta method for the screening of Plant Growth Promoting Rhizobacteria to control plant pests and pathogens
Abstract: Plant pests and diseases are among the most important biotic agents causing serious losses and damages to agricultural production. A number of different strategies are currently being employed to manage and to control them, especially using pesticides. As we know, the synthetic pesticides have a negative effect on environment and health. This leads to the enormous interest in finding effective non chemical alternatives to protect plants against pests and diseases, such as biocontrol agents (BCA). One group of important BCA is the Plant Growth Promoting Rhizobacteria (PGPR). This paper explains the effective method to find PGPR strains, which have the ability to control plant pest and diseases, and also to increase growth and yield of plant. This method is based on in planta selection of PGPR from healthy plants in pest or disease endemic areas. This approach focuses on general forms of disease suppression, especially indirect mechanisms, such as induced systemic resistance. We characterized only the best PGPR strains which have several mechanisms, such as to control plant pest and disease and to promote growth and to increase yield of plants. This technique has the possibility to find the new, easy and cheap biocontrol organisms. Our previous study showed that PGPR strains from the rhizosphere of healthy plants could control plant pests and pathogens and also increase plant growth and yield, such as 10 PGPR strains from rhizosphere of healthy ginger to control Ralstonia solanacearum race 4; 13 PGPR strains from rhizosphere of healthy chili to control bacterial wilt disease; 3 indigenous PGPR strains and 2 non-indigenous PGPR’s strains to control the armyworm on onion; 12 PGPR strains from rhizosphere of healthy onion to control Xanthomonas leaf blight disease. The best PGPR strains from onion’s rhizosphere were identified as Pantoea agglomerans, Enterobacter cloacae, Stenotrophomonas sp., Serratia marcescens, five Bacillus thuringiensis strains, B. cereus, B. weihenstephanensis and Bacillus sp. We have obtained the new information, that B. thuringiensis strains could control Xanthomonas leaf blight on onion. As we know, these bacteria commonly act as entomopathogen to control insect pest.