Biological control of postharvest fungal diseases in lemons using native killer yeasts

JULIA PEREZ IBARRECHE; MARÍA FLORENCIA PEREZ; JACQUELINE RAMALLO; MILENA SEPULVEDA; JULIÁN RAFAEL DIB

Conferencia; 6th International Conference on Biotechnology for the Wellness Industry (ICBWI); 2016

Economic losses caused by postharvest diseases represent one of the primary problems of citrus industry worldwide. The main diseases affecting citrus are the "green mold" and "blue mold", produced by Penicillium digitatum and Penicillium italicum, respectively. These fungi are wound pathogens and cause a soft and wet rot that quickly deteriorates the organoleptic characteristics of the fruit. To control citrus postharvest diseases, the most commonly used method is the application of synthetic fungicides because of its low cost, ease of application and effectiveness. Among them, thiabendazole and imazalil are the most used, however the emergence of resistant strains limits the efficiency. In addition, their use is increasingly restricted due to their carcinogenic effects, residual toxicity, long period of degradation and environmental pollution they generate, combined with barriers to international trade.Because of these reasons biological control has been developed as an alternative to synthetic fungicides, reaching promising results by using antagonistic microorganisms to control postharvest diseases. Yeasts stand out among known antagonists with the advantages of not producing spores or mycotoxins, with simple nutritional requirements and ease large-scale production. These microorganisms can colonize dry surfaces for long periods and even resist to several pesticides used in postharvest stage. Furthermore, special attention has been paid to some yeasts showing the ability to secrete protein toxins or glycoprotein that are lethal to susceptible microbial cells, which are known as killer yeasts.The aim of this work was to evaluate native yeasts with "killer" phenotype as biological control agents of post-harvest fungal diseases in lemons and as alternatives to the use of chemical agents that can be harmful to humans as well as to the environment.437 yeast strains were previously isolated in our lab from citrus plants in Tucuman city, which is known as one of the major producer and manufacturer of lemons in the world. 8.5% of the yeasts showed a killer phenotype. In vitro antagonistic activity of killer isolates against phytopathogenic fungi P. digitatum, P. italicum and Phomopsis citri was evaluated. According to molecular identification, based on the 26S rDNA D1/D2 domain sequences analysis, strains were identified belonging to the genera Saccharomyces, Wickerhamomyces, Kazachstania, Pichia, Candida and Clavispora. Subsequently, killer strains that had caused the maximum in vitro inhibition of P. digitatum were selected and their ability to inhibit the fungus in in vivo assays in lemons were evaluated regarding extent and type of control and comparing with the protective effects of a commercial product based on Candida oleophila. Two strains of Pichia and one strain of Wickerhamomyces caused a significant growth inhibition (p