Biocontrol of Avocado Dematophora Root Rot by Antagonistic Pseudomonas fluorescens PCL1606 Correlates With the Production of 2-Hexyl 5-Propyl Resorcinol

Abstract

A collection of 905 bacterial isolates from the rhizospheres of healthy avocado trees was obtained and screened for antagonistic activity against Dematophora necatrix, the cause of avocado Dematophora root rot (also called white root rot). A set of eight strains was selected on the basis of growth inhibitory activity against D. necatrix and several other important soilborne phytopathogenic fungi. After typing of these strains, they were classified as belonging to Pseudomonas chlororaphis, Pseudomonas fluorescens, and Pseudomonas putida. The eight antagonistic Pseudomonas spp. were analyzed for their secretion of hydrogen cyanide, hydrolytic enzymes, and antifungal metabolites. P. chlororaphis strains produced the antibiotic phenazine-1-carboxylic acid and phenazine-1-carboxamide. Upon testing the biocontrol ability of these strains in a newly developed avocado-D. necatrix test system and in a tomato-F oxysporum test system, it became apparent that P. fluorescens PCL1606 exhibited the highest biocontrol ability. The major antifungal activity produced by strain P. fluorescens PCL1606 did not correspond to any of the major classes of antifungal antibiotics produced by Pseudomonas biocontrol strains. This compound was purified and subsequently identified as 2-hexyl 5-propyl resorcinol (HPR). To study the role of HPR in biocontrol activity, two Tn5 mutants of P. fluorescens PCL1606 impaired in antagonistic activity were selected. These mutants were shown to impair HRP production and showed a decrease in biocontrol activity. As far as we know, this is the first report of a Pseudomonas biocontrol strain that produces HPR in which the production of this compound correlates with its biocontrol activity.

Organic Amendments to Avocado Crops Induce Suppressiveness and Influence the Composition and Activity of Soil Microbial Communities

“…S2 in the supplemental material). The disease index (DI) in each treatment was calculated according to the method described by Cazorla et al (52). The experiment was considered finished 165 days postinoculation in both of the assays.…”

Iturin A is the principal inhibitor in the biocontrol activity ofBacillus amyloliquefaciensPPCB004 against postharvest fungal pathogens

“…Recently, the use of biological control agents has received great attention because of the ability of such strains to suppress different plant diseases involving various modes of action (Cazorla et al 2006;Liu et al 2009;Sharma et al 2009) and the possibilities to be integrated with other control methods (Nofal and Haggag 2006;Pertot et al 2008;Correa et al 2009). Among the most promising candidates for bacterial biocontrol agents are several species of the genus Bacillus.…”

Detection of Phenazines from UPMP3 Strain of Pseudomonas aeruginosa and its Antagonistic Effects against Ganoderma boninense

“…The rhizospheric bacteria, different species of Pseudomonas sp., are very important sources for the detection of antimicrobial compounds and their practical use as biopesticides (Cazorla et al, 2006). UPMP3 strain of P. aeruginosa produced organic compounds during the incubation period which was detected by the color change of the culture medium.…”