Sonia Diskin

Pathogenic fungi, as Botryosphaeriaceae family, can penetrate during flowering and endophytically colonize the stem of mango fruit (Mangifera indica) without causing any visible symptoms. Those fun...

Stem-end rot (SER) is a serious postharvest disease of mango fruit grown in semi-dry area. Pathogenic and non-pathogenic microorganisms endophytically colonize fruit stem-end. As fruit ripens, some pathogenic fungi switch from endophytic colonization to necrotrophic stage and cause SER. Various pre/post-treatments may alter the stem-end community and modify SER incidence. This study investigates the effects of harvesting mango with or without short stem-end on fruit antifungal and antioxidant activities, the endophytic microbiome, and SER during fruit storage. Our results show that harvesting mango with short stem significantly reduced SER during storage. At harvest, fruit harvested with or without stem exhibit a similar microorganisms community profile. However, after storage and shelf life, the community of fruit without stem shifted toward more SER-causing-pathogens, such as Lasiodiplodia, Dothiorella, and Alternaria, and separated from the community of fruit with stem. This change correlated to the high antifungal activity of stem extract that strongly inhibited both germination and growth of Lasiodiplodia theobromae and Alternaria alternata. Additionally, fruit that was harvested with stem displayed more antioxidant activity and less ROS. Altogether, these findings indicate that harvesting mango with short stem leads to higher antifungal and antioxidant activity, retaining a healthier microbial community and leading to reduced postharvest SER.

After harvest, the fruit ripens and stem-end rot (SER) starts to develop, leading to significant fruit losses. SER is caused by diverse pathogenic fungi that endophytically colonize the stem during fruit development in the orchard or field and remain quiescent until the onset of fruit ripening. During the endophytic-like stage, the pathogenic fungus colonizes the phloem and xylem of the fruit stem-end; after fruit ripening, the fungus converts to a necrotrophic lifestyle, while colonizing the fruit parenchyma, and causes SER. The fruit stem-end is colonized not only by pathogenic fungi, but also by various nonpathogenic endophytic microorganisms, including fungi, yeast and bacteria. However, little is known about the fruit stem-end endophytic microbiome, which could contain new and existing biocontrol agents. To control fruit SER, treatments such as ripening inhibition, harvesting with the stem, application of chemical or biological fungicides, or physical control such as heat treatments, cold storage, or exposure to light have been suggested. This review focuses on the characterization of SER pathogens, the stem-end microbiome, and different pre- and postharvest practices that could control fruit SER.

During storage and ripening, mango fruit develop stem-end rots (SER) that reduce quality, causing significant losses of harvested fruit. The presented results indicate that pathogens, endophytically colonizing the fruit’s stem end, awaken during fruit ripening and cause SER. The main pathogens causing SER in mango grown in Israel were found to be Alternaria alternata and Lasiodiplodia theobromae. Confocal analysis of the sliced stems indicated that the pathogens endophytically colonize the phloem of the fruit’s stem end; they branch into the fruit parenchyma when the pathogen switches to its actively pathogenic stage. We show that the stem ends are also colonized by other microorganisms, including fungi, yeast, and bacteria, which do not cause any apparent symptoms and are considered as true endophytes. Stem-end microbiomes of red (resistant) compared with green (susceptible) mango stored at optimal and suboptimal temperatures were deep sequenced for fungi and bacteria using internal transcribed spacer and 16S, respectively. Our results showed that both fungal and bacterial community changes are dependent on fruit peel color, storage duration, and storage temperature. The stem-end microbiota seems to be very dynamic in terms of interactions and changes. For example, in susceptible fruits, as green mango compared with red mango and in fruit after storage compared with harvested fruit, the abundance of Alternaria (Pleosporaceae) pathogens increased. This increase in pathogenic fungi was correlated with the increased occurrence of SER. In those two scenarios, before the rot developed, the increased amount of fungi was correlated with an increased abundance of chitin-degrading Chitinophagaceae bacteria. In summary, our results show that various conditions modify the microbial community at the stem end and can reduce postharvest SER.