Botrydial confers Botrytis cinerea the ability to antagonize soil and phyllospheric bacteria.

The role of the sesquiterpene botrydial in the interaction of the phytopathogenic fungus Botrytis cinerea and plant-associated bacteria was analyzed. From a collection of soil and phyllospheric bacteria, nine strains sensitive to growth-inhibition by B. cinerea were identified. B. cinerea mutants unable to produce botrydial caused no bacterial inhibition, thus demonstrating the inhibitory role of botrydial. A taxonomic analysis showed that these bacteria corresponded to different Bacillus species (six strains), Pseudomonas yamanorum (two strains) and Erwinia aphidicola (one strain). Inoculation of WT and botrydial non-producing mutants of B. cinerea along with Bacillusamyloliquefaciens strain MEP218 in soil demonstrated that both microorganisms exert reciprocal inhibitory effects; the inhibition caused by B. cinerea being dependent on botrydial production. Moreover, botrydial production was modulated by the presence of B. amyloliquefaciens MEP218 in confrontation assays in vitro. Purified botrydial in turn, inhibited growth of Bacillus strains in vitro and cyclic lipopeptide (surfactin) production by B. amyloliquefaciens MEP218. As a whole, results demonstrate that botrydial confers B. cinerea the ability to inhibit potential biocontrol bacteria of the genus Bacillus. We propose that resistance to botrydial could be used as an additional criterion for the selection of biocontrol agents of plant diseases caused by B. cinerea.

Survival of native Pseudomonas in soil and wheat rhizosphere and antagonist activity against plant pathogenic fungi.

Survival of Pseudomonas sp. SF4c and Pseudomonas sp. SF10b (two plant-growth-promoting bacteria isolated from wheat rhizosphere) was investigated in microcosms. Spontaneous rifampicin-resistant mutants derived from these strains (showing both growth rate and viability comparable to the wild-strains) were used to monitor the strains in bulk soil and wheat rhizosphere. Studies were carried out for 60 days in pots containing non-sterile fertilized or non-fertilized soil. The number of viable cells of both mutant strains declined during the first days but then became established in the wheat rhizosphere at an appropriate cell density in both kinds of soil. Survival of the strains was better in the rhizosphere than in the bulk soil. Finally, the antagonism of Pseudomonas spp. against phytopatogenic fungi was evaluated in vitro. Both strains inhibited the mycelial growth (or the resistance structures) of some of the phytopathogenic fungi tested, though variation in this antagonism was observed in different media. This inhibition could be due to the production of extracellular enzymes, hydrogen cyanide or siderophores, signifying that these microorganisms might be applied in agriculture to minimize the utilization of chemical pesticides and fertilizers.