Evaluation of Sown Cover Crops and Spontaneous Weed Flora as a Potential Reservoir of Black-Foot Pathogens in Organic Viticulture

SIMPLE SUMMARY: Black-foot is an important grapevine disease caused by a soil-borne fungal pathogens complex, which are collectively known as Cylindrocarpon-like asexual morphs. In organic viticulture, both sown and native cover crop species can act as potential reservoirs of black-foot associated fungi. In our study a wide survey of cover crops grown in organic vineyards was conducted over a diverse range of climatic zones in six different European countries to acquire information about the presence of Cylindrocarpon-like asexual morphs on their roots. Several fungal species associated with black-foot disease were found on some of the cover crops evaluated in all the countries. These results provide valuable information for a reasoned choice of cover crop species, or a species mix, that can be used in organic viticulture. This is particularly important for maximizing their benefits and reducing potential problems in vineyards. ABSTRACT: (1) Background. An extensive survey of grapevine-sown cover crops and spontaneous weed flora was conducted from 2019 to 2020 in organic vineyards in six European countries (France, Italy, Romania, Slovenia, Spain, Switzerland). Our main objective was to detect and identify the presence of Cylindrocarpon-like asexual morphs species associated with black-foot disease on their roots. (2) Methods. Fungal isolations from root fragments were performed on culture media. Cylindrocarpon-like asexual morph species were identified by analyzing the DNA sequence data of the histone H3 (his3) gene region. In all, 685 plants belonging to different botanical families and genera were analyzed. Cylindrocarpon-like asexual morphs were recovered from 68 plants (9.9% of the total) and approximately 0.97% of the plated root fragments. (3) Results. Three fungal species (Dactylonectria alcacerensis, Dactylonectria torresensis, Ilyonectria robusta) were identified. Dactylonectria torresensis was the most frequent, and was isolated from many cover crop species in all six countries. A principal component analysis with the vineyard variables showed that seasonal temperatures and organic matter soil content correlated positively with Cylindrocarpon-like asexual morphs incidence. (4) Conclusions. The presence of Cylindrocarpon-like asexual morphs on roots of cover crops suggests that they can potentially act as alternative hosts for long-term survival or to increase inoculum levels in vineyard soils.