Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2011
Publication Date: November 21, 2011
Citation: Janisiewicz, W.J., Pimenta, R.S., Jurick Ii, W.M. 2011. A novel method for selecting antagonists against postharvest fruit decays originating from latent infections. Biological Control. 59:348-389. Interpretive Summary: Biological control of fruit decays using beneficial microorganisms after harvest has been used commercially with a great success for the past fifteen years, and the number of new biocontrol products is increasing. These products were developed to control decays originating from infection of fruit wounds made during harvest and postharvest handling; however, there are no products to control decays developing after harvest from asymptomatic latent infections of sound fruits that occur in the orchard. This is largely due to the lack of research in this area because there are no methods for selecting beneficial microorganisms against this type of infection. We developed a method for selecting such beneficial microorganism based on their ability to colonize artificially induced fungal structures that are involved in the latent infections of stone fruits on parfilm and wax membranes. The microorganisms that are able to colonize the fungus have been further tested for decay control ability on plums with artificially induced latent infections under laboratory conditions. We found several very effective beneficial bacteria that controlled brown rot of plums using this method. Future research will focus on selecting those beneficial microorganisms that are best adapted to conditions occurring during storage and handling of the fruit in packinghouses, and optimizing the biocontrol process.
Technical Abstract: Biological control of fruit decays originating from wound infections after harvest has made great progress during the past two decades and several products are commercially available. However, this is not the case for postharvest decays originating from latent infections which occur in the orchard. This is mainly due to the lack of methodology used to screen and evaluate microbes for biocontrol activity against this type infection. We have developed a method involving interactions between the pathogen structure involved in latent infection (appressorium) and the test microorganism which can evaluated in vitro and then tested for biocontrol activity in situ on fruit. The emphasis was placed on a direct interaction between the pathogen and the potential antagonist. Appressoria of the brown rot pathogen, Monilinia fructicola, were produced on wax membranes or parafilm after depositing drops containing conidia in a 0.25 mM sucrose solution containing 10 mM cAMP and incubating at 18 degrees C for 16 h. This was followed by the addition of the test organism, additional incubation at 24 degrees C for 72 h, and microscopic observations. Microorganisms colonizing appressoria and mycelium were further tested for biocontrol activity on fruit containing artificially induced latent infections. The latent infections were induced by inoculating fruit wrapped in gauze with conidia and kept moist during a 16 h incubation period at 18 degrees C. The fruit were then treated with the potential antagonist, incubated for 24 h at 24 degrees C, after which the gauze was removed, the fruit were incubated for 7 to 10 days at 24 degrees C, and then evaluated for decay development. We found several effective antagonists against brown rot of stone fruits using this approach. The next step is to select those antagonists that are best adapted to conditions occurring during storage and handling of the fruit. This approach may also be adapted to develop biocontrol of latent infections in other fruit/pathogen systems.