Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2001
Publication Date: N/A
Interpretive Summary: Biological control of postharvest decays of fruit using beneficial microorganisms has been in commercial use for the past few years. Efficacy of the biocontrol can be improved greatly if the mechanisms of biological control were better understood. However, past methods did not allow to study in depth mechanisms that operate in a fruit system after harvest. We developed a new laboratory method to study mechanisms of biological control in the postharvest fruit system. By using fruit juice as substrate we simulated natural conditions at the fruit wound. The method allows measurement of nutrients competition between an antagonist and a pathogen. The method is non-destructive, so that the infectivity of a pathogen can be tested after exposure to a biocontrol antagonist. The method can also be used to study other mechanisms of biocontrol, where direct contact between an antagonist and a pathogen is not required.
Technical Abstract: Biocontrol agents may compete with pathogens for nutrients and space to delay or prevent decay of fruits after harvest. These mechanisms of biocontrol have been difficult to study because no method has been available to determine the significance of each of the components of competition. We developed a non-destructive method using tissue culture plates with cylinder inserts containing defusing membrane at one end to study competition for nutrients without competition for space. Other biocontrol mechanisms in which direct contact between an antagonist and a pathogen is not required can also be studied. The method was used to determine the competition between a yeast biocontrol agent and Penicillium expansum for limited nutrients in apple juice, during 24 h incubation, simulating a fruit wound. An antagonist depleted amino acids and inhibited germination of P. expansum conidia. Exposing these conidia to fresh apple juice increased conidia germination to the level comparable to that exhibited by conidia which were not exposed to the antagonist. Because the culture plate method was non-destructive, a follow-up experiment in an agar diffusion test was conducted. Juice, in which the antagonist grew, did not inhibit germination of P. expansum conidia that were seeded on the plates. This corroborates findings from the culture plate method that inhibition of the conidia germination resulted from competition for nutrients. The new method can be coupled with existing techniques to improve understanding of antagonist-pathogen interaction for biocontrol of postharvest diseases.