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.