Microbiome Alterations Are Correlated with Occurrence of Postharvest Stem-End Rot in Mango Fruit

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 altemata 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 Attemaria (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.