Enhancing Biocontrol Activity 2341 In Combination with Other Treatments

Under the experimental conditions used by some researchers, there have been occurrences of disappointing results when the currently registered biocontrol products were used as stand-alone treatments [44-46]. Research on biocontrol organisms, whether for pre- or postharvest uses, is typically reductionist — testing one product versus another in stand-alone trials. When the biocontrol agent does not perform equally well as the chemical in these stand-alone trials, the biocontrol agent may be pronounced inferior, and that is usually the end of the story. Research shows that mixtures of biocontrol agents with other biorational products can provide excellent efficacy not seen in stand-alone trials. For example, Conway et al. showed that they could eliminate postharvest decay caused by Colletotrichum acutatum on apples with a combination of either of two antagonists and heat [47]. Either antagonist alone eliminated decay caused by Penicillium expansum, but the two were more effective together. Combinations with chemical agents should be tested as well to prevent resistance, increase efficacy, and reduce the amount of chemicals that could be used. Continued funding for research of this type will increase the probability that biocontrol agents will be more widely adopted for postharvest uses. For this reason, combination with other treatments might be envisaged to achieve more consistent and robust disease control. Biocontrol agents are not necessarily incompatible with chemical fungicides, which can often be used at reduced rate in such situations. The use of several antagonistic bacteria and yeasts, including the agents in BioSave and Aspire, has been shown to be compatible with postharvest chemical fungicides at full or reduced rates, and such combinations have resulted in higher efficacy than biocontrol agents alone [5,7,12,44-46,48,49]. Lowering the use rates of chemical fungicides, while helping reduce chemical residues on fruit, can also compensate for possible shortcomings of biofungicides against early or incipient infections and sensitivity to environmental conditions.

The combination of biocontrol agents with other storage technologies is not only desirable, but necessary. Biocontrol agents should be compatible with low temperature and controlled or modified atmosphere storage, as these methods are commonly used to extend the shelf life of fruits and vegetables. So far, reports of combining antagonistic yeasts with controlled or modified atmospheres have been positive, improving the performance of yeasts in high CO2 and low O2 compared to storage in air [11,12]. Several antagonistic yeasts are capable of growth and survival on fruit held in cold storage [3,5,49,50], which make them compatible for use on commodities that require rapid chilling and storage at low temperatures. Combination of biocontrol agents with other cultural disease control methods like fruit curing [51] or heat treatment [52,53] could also be advantageous depending on the commodity. Finally, the combination of two or more antagonists with different characteristics, which could be considered as mixtures of microorganisms, can be more effective in controlling decay than single agents [3,10]. While it has been suggested that the postharvest environment can be manipulated somewhat to accommodate biological control, it is likely that the most successful biofungicides will be effective under the normal handling and storage conditions used for each commodity.

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