Microorganisms, application timing and fractions as players of the milk-mediated powdery mildew management

Milk has proven to be efficient in powdery mildew (PM) control, but little has been reported on the modulators of its efficacy. This work aimed at studying milk's preventive and curative activities on PM control, determining the changes of fungal structures after milk treatment, surveying the leaf microbial community after milk treatment and testing the milk's fractions and sources for PM control. A preventive activity of milk was only observed for plants treated with milk at 30% concentration, whilst a reduced number of mildew colonies were recorded on leaves treated with conidia exposed to milk before inoculation. Scanning electron microscopy revealed damaged hyphae and conidiophores, a deposit over conidia and abundant yeast-like microorganisms for milk-treated plants. The microbial community was higher on plants treated with milk than those either treated with a fungicide or water and a yeast isolated from milk-treated leaves controlled the disease as well as milk. Both raw and pasteurized milk were the most efficient sources, and the lactose fraction had an effect similar to ultrahigh temperature (UHT) milk. Our results shed light on important aspects that should be considered when using milk for PM management.

► Milk has a direct activity on Podosphaera xanthii and a weak to absent preventive one. ► Milk treatment stimulates the buildup of the microbial community and yeasts have biocontrol activity. ► Any milk source has the potential for the disease control. ► The control efficacy of milk sources drops with the heat treatment. ► A promising milk fraction for the disease control is lactose.