Partial resistance might select for increased aggressiveness of downy mildew

A fundamental milestone of task 2.1 (Durability of grape resistance to major fungal diseases) was the cross inoculations of susceptible and tolerant genotypes with powdery and downy mildew (DM) strains which, among its goals, plans to address the hypothesis that partial resistance might select for increased aggressiveness of downy mildew (DM). Sixty (60) DM isolates were obtained from resistant genotypes and 110 from susceptible ones. Preliminary results confirm: i) an overall erosion of plant resistance; ii) more sporangia yet of smaller size grew on isolates from resistant genotypes and iii) shorter latent period on Bronner and Prior. Such findings seem to hint towards increased aggressiveness by DM. In terms of disease epidemics on resistant varieties, disease data on resistant varieties (Johaniter, Bronner, Solaris, Rpv1/Rpv3, 7589) will be collected soon under the aim of combining resistance with fungicide applications to control downy mildew and black-rot.