Isolation and characteristics of Pseudomonas fluorescens to inhibit Phytophthora palmivora causing rot disease in durian

Plant growth promoting Rhizobacteria (PGPR) have long been selected as biocontrol agents for plants. The PGPR are beneficial bacteria that live in plant roots and enhance plant growth by various of mechanisms. The PGPR have many species of the bacterial genus Pseudomonas, in which the Pseudomonas fluorescens strains is suitable for application as a biocontrol agent due to its abundance in natural soil and plant root systems. Pseudomonas fluorescens strains have important characteristics such as the ability to adhere to soil particles and to rhizomes, the ability to synthesize antibiotics, and to produce hydrolytic enzymes. Furthermore, P. fluorescens strains also possess plant growth promoting characteristics such as proteolysis, phosphate solubilization, iron chelation, and phytohormone production. Durian is a crop that has been expanded in Southeast Asian countries but the rate of durians infected with root, stem and fruit rot caused by P. palmivora is quite large. In this study, five native P. fluorescens isolates were isolated from 70 soil and rhizome samples collected from 10 durian growing provinces and evaluated for their ability to antagonize P. palmivora in petri plates. These isolates were gram negative, small, single isolated rods without sporulation when observed under microscope. All of them tested positive for catalase test, oxidase test, starch hydorolysis, gelatine liquefaction, H2S, citrate utilization and negative with indole, Voges-proskauers, methyl red. All of 5 native P. fluorescens isolates were capable of phosphate solubilizing activity, N2 fixation, siderophore and IAA production. The study showed that P. fluorescens P. fDN strain was able to inhibit P. palmivora causing rot disease in durian with 51.85% inhibition of radial growth.