Biological control of postharvest fungal decays in citrus: a review

Citrus (Citrus spp.) species produce a variety of fruits that are popular worldwide. Citrus fruits, however, are susceptible to postharvest decays caused by various pathogenic fungi, including Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, Aspergillus niger, and Aspergillus flavus. Decays resulting from infections by these pathogens cause a significant reduction in citrus quality and marketable yield. Biological control of postharvest decay utilizing antagonistic bacteria and fungi has been explored as a promising alternative to synthetic fungicides. In the present article, the isolation of antagonists utilized to manage postharvest decays in citrus is reviewed, and the mechanism of action including recent molecular and genomic studies is discussed as well. Several recently-postulated mechanisms of action, such as biofilm formation and an oxidative burst of reactive oxygen species have been highlighted. Improvements in biocontrol efficacy of antagonists through the use of a combination of microbial antagonists and additives are also reviewed. Biological control utilizing bacterial and yeast antagonists is a critical component of an integrated management approach for the sustainable development of the citrus industry. Further research will be needed, however, to explore and utilize beneficial microbial consortia and novel approaches like CRISPR/Cas technology for management of postharvest decays.