ARS | Publication request: Aureobasidium pullulans as a biocontrol agent of postharvest pathogens of apples in Uruguay

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 12, 2009
Publication Date: August 20, 2009
Citation: Vero, S., Garmendia, G., Gonzalez, M., Garat, F., Wisniewski, M.E. 2009. Aureobasidium pullulans as a biocontrol agent of postharvest pathogens of apples in Uruguay. Biocontrol Science and Technology. 19:1033-1049.

Interpretive Summary: Some fruits are highly susceptible to postharvest rots and appear to have very little resistance to specific fungal pathogens. The application of chemical fungicides are required to prevent the economic losses that would occur as a result of these postharvest infections; however, consumers prefer a reduction in the use of chemical pesticides. The use of antagonistic microorganisms as biocontrol agents to inhibit postharvest pathogens has shown great potential. This research describes the isolation, identification, and evaluation of ten strains of the yeast, Aureobasidium pullalans as a biocontrol agent to control postaharvest rots of apple caused by the fungi, Penicillium exanpsum and Botrytis cinerea. Of the ten strains tested, strain ApB proved to be the most effective in lab tests and packing house tests conducted in Uruguay. The ApB strain did not grow at temperatures above 35 degrees C which is an important human safety factor. The strain was also resistant to chemical postharvest fungicides indicating that it could be used in combination with a low-dose of these chemicals or would not be adversely affected by chemical residues potentially present in a commercial environment. The ability of these strains to scavenge iron from the environment may give the yeast an important competitive advantage over the postharvest pathogens present and therefore, may play an important role in its mechanism of action. This research lays the foundation for the development of an alternative approach to managing postharvest diseases of apple in Uruguay and reduce consumer exposure to synthetic, postharvest fungicides.

Technical Abstract: The yeast, Aureobasidium pullulans, was the microorganism most frequently recovered from the surface of apple fruit (cv. Red Delicious) stored in commercial cold chambers for six months. In the present work, ten isolates of Aureobasidium pullulans were assayed to determine if they could control blue and grey mold disease of apple during cold storage. Although nine of ten isolates significantly reduced the percentage of decayed wounds when compared to the control, one of them, designated isolate ApB, showed the highest levels of protection. ApB was able to grow in a wide range of temperatures lower than 35 degrees C, which is an important human health safety factor. ApB was resistant to thiabendazole, iprodione and imazalil, the most commonly commercially applied fungicides in postharvest treatment of apples in Uruguay. Regarding the mechanisms of action of the selected biocontrol agent, lytic enzymes did not seem to play a central role. ApB depleted iron from nutrient media, which may be an important aspect of its ability to inhibit Botrytis cinerea. Further experiments are needed, however, to determine if the depletion of iron is caused by the production of siderophores, by the immobilization of iron in an insoluble pigment, or a combination of both.