Postharvest microbiota dynamics of mango fruit stem-end in response to light, temperature and during storage
Stem-end rots (SER) develop in harvested mangos during fruit ripening and cause significant losses. SERs are caused by pathogenic fungi (e.g. Colletotrichum gloeosporioides, Alternaria alternata, Lasiodiplodia theobromae, Neofusicoccum, Dothiorella, Phomopsis mangiferae, and others) that endophytically colonize fruit stems during fruit development in the orchard and remain quiescent until the onset of fruit ripening. This work was conducted to characterize the endophytic microbiota in mango fruit stem-end tissue and study the effect of different postharvest treatments on the composition of bacterial and fungal communities. Microscopic observations showed that during the quiescent stage various fungi colonize the phloem of fruit stem-end, and after switching to the pathogenic stage they expand to the fruit parenchyma surrounding the stem, causing SER. Interestingly, fruits that were subjected to high light in the orchard developed less SER after storage. These fruits accumulated anthocyanins leading to red color peel, which was correlated with resistance to both anthracnose and SER. The bacterial and fungal microbiomes in stem-end of red and green mango fruit stored at different temperatures were examined using universal bacterial and fungal primers (16S and ITS respectively). Bioinformatic data analysis showed that the community compositions of the fungi and bacteria in the mango stem-end were significantly modified during storage, in response to different storage temperatures and in response to high light in the orchard. For example, Pleosporaceae (Alternaria) was the most abundant fungi in green (susceptive fruit) that was not exposed to sunlight or during storage (fruit ripening). This change in fungal composition was accompanied with increased occurrence of SER. Soon before the development of SER, the increased amount of fungi was correlated with the increase in abundance of chitin degrading Chitinophagaceae bacteria. Collectively, our results show that pre and post-harvest treatments modify microbial community in the stem-end and could be associated with reducing postharvest SERs.