The effects of some CAA and QoI fungicides on disease development by Plasmopara viticola, zoospore release and ε-viniferin accumulation

This study evaluated the efficacy of two fungicide mixtures, azoxystrobin + difenoconazole and mandipropamid + zoxamide, in protecting grapevine leaves against Plasmopara viticola. The effects of different fungicide doses on the P. viticola population collected from various grapevine cultivars were investigated by assessing sporulation area on detached leaves, zoospore release, zoospore mobility, and ε-viniferin accumulation. The EC50 value for mandipropamid + zoxamide was 0.031 µg ml-1, yielding 97.73% inhibition of sporulation area at 1 µg ml-1. In contrast, the azoxystrobin + difenoconazole mixture exhibited an EC50 value of 40 µg ml-1 and achieved 92.82% inhibition of sporulation area at 300 µg ml-1. The G143A mutation, a known marker for fungicide resistance, was found using allele-specific polymerase chain reaction (ASPCR). Furthermore, the mandipropamid + zoxamide mixture promoted ε-viniferin accumulation at a low concentration (0.01 µg ml⁻¹) while significantly inhibiting zoospore mobility and release. The azoxystrobin + difenoconazole mixture reduced the number of motile zoospores by 84% at 10 µg ml⁻¹, suggesting its potential to lower infection risk under field conditions. These findings suggest that, in addition to their direct effects on pathogen development, fungicides should also be evaluated for their impact on zoospore mobility, a critical stage in the infection cycle, to enhance sustainable disease management strategies.