Antagonistic Potential of Fluorescent Pseudomonads and Control of Crown and Root Rot of Cucumber Caused by Phythophtora drechsleri

In this study, 200 isolates of fluorescent pseudomonads were isolated from different fields of East and West Azarbaijan and Ardebil provinces of Iran. These bacterial isolates were screened on the basis of a dual culture assay, the presence of known antibiotic genes, and their ability to successfully colonize roots and to promote plant growth. Twelve isolates exhibited 30% or more inhibition of mycelia growth of P. drechsleri. Genes encoding production of the antibiotics 2,4-diacetylphloroglucinol, phenazine-l-carboxylic acid, and pyoluteorin were detected in some strains but none of the strains possessed the coding gene for production of antibiotic pyrrolnitrin. In an in vitro test for root colonization, the population density on roots of plants treated with most of the above strains was more than 6 log(10) CFU g(-1) roots, with a maximum of 7.99 log(10) CFU g(-1) roots for strain 58A. Most of the strains promoted significant plant growth in comparison to non-treated controls. In green house studies, the percentage of healthy plants in pots treated with strains 58A and 8B was 90.8% and 88.7%, respectively. The difference between these treatments and treatment with the fungicide metalaxyl was not significant.