Effect of Sterol Biosynthesis Inhibitors and Azole-Type Inducers on Growth and Development of Plasmopara Viticola on Grapevine

The study tested the effects of azole fungicides and brassinosteroid biosynthesis inhibitors on the growth and spore production of Plasmopara viticola, the downy mildew pathogen in grapevines. It was found that applying demethylation inhibitors (DMIs) and azole-type inducers two days before inoculation delayed mycelial growth initially but did not affect it by day 5 or 7, and only weakly reduced sporulation. These effects were absent when applied during or after inoculation, indicating that azole treatments did not significantly impact infections in field conditions. However, inhibiting plant brassinosteroid metabolism with finasteride significantly reduced sporulation, suggesting that plant sterols or related processes play a role in pathogen reproduction.