Chilean Botrytis cinerea Isolates with Reduced Sensitivity to Fludioxonil Exhibit Low to Null Fitness Penalties.

The main phytosanitary problem for table grape production in Chile is gray mold caused by the fungus Botrytis cinerea. To manage this issue, the primary method utilized is chemical control. Fludioxonil, a phenylpyrrole, is highly effective in controlling B. cinerea and other plant pathogens. Consistently, there have been no field reports of reduced efficacy of fludioxonil; however, subpopulations with reduced sensitivity to fludioxonil are on the rise globally, as per increasing reports. Our study involved a large-scale evaluation of B. cinerea's sensitivity to fludioxonil in the Central Valley of Chile's primary table grape production area during the growing seasons from 2015 to 2018. Out of 2,207 isolates, only 1.04% of the isolates (n = 23) exceeded the sensitivity threshold value of 1 µg/ml. Remarkably, 95.7% are concentrated in a geographic region (Valparaíso Region). Isolates with reduced sensitivity to fludioxonil showed growth comparable with sensitive isolates and even more robust growth under nutritional deficit, temperature, or osmotic stress, suggesting greater environmental adaptation. When table grape detached berries were stored at 0°C, isolates less sensitive to fludioxonil caused larger lesions than sensitive isolates (2.82 mm compared with 1.48 mm). However, the lesions generated by both types of isolates were equivalent at room temperature. This study found no cross-resistance between fludioxonil and fenhexamid, an essential fungicide integrated with fludioxonil in Chilean B. cinerea control programs. All the Chilean isolates with reduced sensitivity to fludioxonil were controlled by the fludioxonil/cyprodinil mixture, a commonly employed form of fludioxonil. The cyprodinil sensitivity in the isolates with reduced sensitivity to fludioxonil explains their low field frequency despite their null fitness penalties. However, the emergence of fludioxonil-resistant isolates inside the Chilean B. cinerea population demands a comprehensive analysis of their genetic bases, accompanied by monitoring tools that allow the permanence of field fludioxonil efficacy.

Impact of a pesticide cocktail (fenhexamid, folpel, deltamethrin) on the abundance of Glomeromycota in two agricultural soils.

Pesticide contamination of the environment can result from agricultural practices. Persistence of pesticide residues is a threat to the soil biota including plant roots and beneficial microorganisms, which support an important number of soil ecosystem services. Arbuscular mycorrhizal fungi (AMF) are key symbiotic microorganisms contributing to plant nutrition. In the present study, we assessed whether AMF could indicate eventual side effects of pesticides when directly applied to field soils. We evaluated the ecotoxicological impact of a cocktail of three commonly used agricultural pesticides (fenhexamid, folpel, deltamethrin) on the abundance and composition of the AMF community in vineyard (Montagne de Saint-Emilion) and arable (Martincourt) soils subjected to different agricultural practices. The dissipation of applied pesticides was monitored by multiresidual analyses to determine the scenario of exposure of the AMF community. Diversity analysis before application of the pesticide cocktail showed that the AMF communities of vineyard soils, subjected to mechanical weeding or grass cover, and of the arable soil subjected to intensive agriculture, were dominated by Glomerales. Ribotypes specific to each soil and to each agricultural practice in the same soil were found, with the highest abundance and diversity of AMF being observed in the vineyard soil with a grass-cover. The abundance of the global AMF community (Glomeromycota) and of three taxa of AMF (Funneliformis mosseae, Claroideoglomus etunicatum/C. claroideum) was evaluated after pesticide application. The abundance of Glomeromycota decreased in both soils after pesticide application while the abundance of Claroideoglomus and F. mosseae decreased only in the arable soil. These results show that higher doses of pesticide exposure did not affect the global abundance, but altered the composition, of the AMF community. Resilience of the AMF community composition was observed only in the vineyard soil, where F. mosseae was the most tolerant taxon to pesticide exposure.