Effect of Biological and Chemical Treatments During Flowering on Stem-End Rot Disease, and Mango Yield.

Pathogenic fungi, as the Botryosphaeriaceae family, can penetrate during flowering and endophytically colonize the stem of mango fruit (Mangifera indica) without causing any visible symptoms. Those fungi become active during abiotic stress or fruit ripening and cause stem and inflorescence dieback or fruit stem-end rot (SER) fungal disease. We hypothesized that anti-fungal treatments during the main event of Botryosphaeriaceae penetration would reduce the disease. Initially, we showed that treatments with the fungicide "Switch" (fludioxonil and cyprodinil) during orchard flowering (cv. Keitt and Shelly) reduced the occurrence of pathogenic fungi in the fruit stem-end and significantly reduced fruit's incidence of SER disease. As mango orchards are sprayed weekly against powdery mildew (PM) disease during flowering, we combined two treatments against PM disease with two treatments against both PM- and SER-causing pathogens. Application of biological treatments of the fungicide "Serenade" (Bacillus subtilis) or chemical treatments of the fungicides "Luna Tranquility" (fluopyram and pyrimethanil) or "Switch" during flowering in 'Shelly' and 'Keitt' mango orchards significantly reduced inflorescence/stem dieback (up to 50%) and fruit drop and significantly increased the number of fruit per tree, which led to a significant increase in yield, up to 41%, in heavily infected orchards. In addition, this application during flowering (March to April) affected post-harvest fruit quality (August to September) by a significant (P < 0.005) reduction of the incidence and the severity of stem-end rot disease and even fruit side-rot disease, without affecting fruit ripening and other quality parameters. While all fungicides were effective, the chemical fungicides were more effective than the biological fungicide. Thus, changing the PM fungicide regime to control Botryosphaeriaceae penetration during mango orchard flowering led to reduced inflorescence/stem dieback, reduced fruit drop, increase in yield, and minimized post-harvest decay.

Harvesting Mango Fruit with a Short Stem-End Altered Endophytic Microbiome and Reduce Stem-End Rot.

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.