Survey of fluorescent pseudomonads from rhizosphere and rhizoplane of tomato for biocontrol of Clavibacter michiganensis subsp. michiganensis

Tomato bacterial wilt and canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm) is an economically important seed-borne disease in the major tomato growing regions all over the world. Also, this disease is present in northern, northwestern, and central provinces of Iran. This study aimed to isolate fluorescent pseudomonads with efficient antagonistic activity against Cmm from tomato rhizosphere and rhizoplane. In the present study, ninety six fluorescent pseudomonads were isolated from rhizosphere and rhizoplane of tomato plants using King’s medium B agar and tested for antagonistic activity against Cmm by co-inoculation culture in vitro. Seed and roots of tomato transplants were inoculated with representative antagonistic strains and planted in the soil infected by Cmm in greenhouse. The incidence and severity of the disease were assessed on tomato as well as growth parameters. Nineteen strains exhibited inhibitory activity against Cmm in vitro and two selected strains (M1R1 and H1R1) were identified as Pseudomonas putida based on their phenotypic characteristics and partial 16S rRNA gene sequences. These two strains produced siderophore and hydrogen cyanide. In greenhouse, strain M1R1 reduced the disease incidence by 30% and 40% in Superluna and Falat cultivars, respectively. Strain H1R1 reduced the disease incidence by 20% only in Falat cultivar. Strains M1R1 and H1R1 decreased the disease severity by 52.93 % and 10.60 % in Superluna and 47.90 % and 42.88 % in Falat cultivars, respectively. Strain M1R1 increased the growth parameters, including fresh and dry weight, and height of the inoculated plants significantly in comparison with control. These results indicated that rhizospheric fluorescent pseudomonads could be effective agents in the biocontrol of tomato bacterial wilt and canker disease.