Experimental Evidence on The Functional Agent of 2,4-diacetylphloroglucinol in Biocontrol Activity of Pseudomonas fluorescens 2P24

Pseudomonas fluorescens 2P24, a plant disease biocontrol agent isolated from wheat take-all decline soil, is characterized with efficient production of antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG). In this study, the 2,4-DAPG was investigated as a functional agent in antibiosis and biocontrol activity using genetic methods. A 2,4-DAPG negative mutant of P. fluorescnes 2P24, named 2P24MP-ME, was constructed through site-directed mutangensis. The mutant was unable to inhibit the growth of plant pathogens Gaeumannomyces graminis, Rhizoctonia solani and Ralstonia solanacearum in Petri dish and to control the development of tomato bacterial wilt in greenhouse. A plasmid-bearing 2,4-DAPG biosynthetic locus inserted into 2P24MP-ME resulted in a complemented strain 2P24-P. The restored 2,4-DAPG production and strong antibiosis against the phytopathogens were observed in the 2P24-P. Moreover, the efficacy of the 2P24-P for control of tomato bacterial wilt was also recovered to the level of the wild type in the greenhouse. The results indicate that the 2,4-DAPG was one of the key biocontrol factors in P. fluorescens 2P24 and played an important role in controlling tomato bacterial wilt.