|Quecine, Maria Carolina -|
|Pizzirani-Kleiner, A -|
Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2009
Publication Date: June 1, 2009
Citation: Quecine, M., Kidarsa, T.A., Pizzirani-Kleiner, A.A., Loper, J.E. 2009. Roles of rhizoxin and 2,4-diacetylphloroglucinol in suppression of Fusarium spp. by the rhizobacterium Pseudomonas fluorescens Pf-5. Phytopathology. 99(6S):106. Technical Abstract: Pseudomonas fluorescens strain Pf-5 is a rhizosphere bacterium that acts as a biocontrol agent of soilborne plant diseases and produces at least 10 different secondary metabolites, including several with antifungal properties. We derived site-directed mutants of Pf-5 with single and multiple mutations in the biosynthetic gene clusters for the antifungal metabolites 2,4-diacetylphoroglucinol (2,4-DAPG), pyrrolnitrin, pyoluteorin, hydrogen cyanide and rhizoxin. These mutants were tested for suppression of the pathogens Fusarium verticillioides and Fusarium oxysporum f. sp. pisi on several culture media. Rhizoxin and 2,4-DAPG were found to be primarily responsible for fungal antagonism by Pf-5. Previously, other workers showed that the mycotoxin fusaric acid (FA), which is produced by many Fusarium species including F. verticillioides, inhibited the production of 2,4-DAPG by Pseudomonas spp. In this study, amendment of the culture medium with FA decreased 2,4-DAPG production of Pf-5 and reduced transcript levels of 2,4-DAPG biosynthetic genes, assessed using RT-qPCR. Therefore, the mycotoxin influenced antibiotic production by Pf-5 at the transcriptional level. Our results demonstrated the importance of two compounds, rhizoxin and 2,4-DAPG, in suppression of Fusarium spp. by Pf-5 and confirmed that an inter-species signaling system mediated by FA influenced 2,4-DAPG production by the bacterial biological control organism.