Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 1996
Publication Date: N/A
Interpretive Summary: During the past decade, the control of postharvest diseases of fruits and vegetables with beneficial microorganisms has made great progress as an alternative to synthetic fungicides, which are becoming less effective, and also face increasing public disapproval. Recently, EPA registered three beneficial microorganisms for the control of major diseases of pome and citrus fruits. This work focused on developing means of enhancing biological control to broaden the spectrum of activity to control other important diseases and to increase reliability and efficacy of the method. Based on ecological studies, we developed a method for selecting beneficial microorganisms from apple fruit, which can be combined to provide control superior to the individual microorganisms. This reduces the rate of application and increase reliability of the method. This concept can also be used to improve biological control in other systems.
A new and very effective approach in selecting antagonists for mixtures with superior biocontrol potential to the individual antagonist has been developed. Microorganisms selected for the mixtures were isolated from exposed apple tissue in weekly intervals during the last 5 weeks before harvest. They were classified and grouped to nutritional clusters on the basis of utilization of 95 carbon sources in Biolog plates using MicoLog and MLCLUST programs, respectively. Yeasts were dominant at all isolation times. Bacteria were isolated only occasionally. All isolates were screened for biocontrol potential against P. expansum on Golden Delicious apple. The most promising antagonists from different clusters were paired, with preference given to those colonizing the same fruit, then colonizing different fruit but at the same time of isolation, and finally to those colonizing various fruit at various times of isolation. From 21 yeast antagonists tested in 13 combinations, four had superior control to the individual antagonists. A combination of antagonist isolates T5-D3 and T5-E2 was consistently superior to the individual application in controlling blue mold on apples. Nutritional profiles of these antagonists based on utilization of 35 carbon and 33 nitrogen sources revealed significant differences in carbon catabolism. These differences caused niche differentiation and allowed populations of both antagonists to flourish in the same wound. This was confirmed by a high level of coexistence in de Wit displacement series, and close to the unity relative yield at all antagonist proportions tested. Combining antagonists on the basis of niche differentiation appears to be an effective method of improving biocontrol of postharvest and probably other diseases.