Effects of agro-pedo-meteorological conditions on dynamics of temperate rice blast epidemics and associated yield and milling losses

Rice blast disease is a threat for European rice growers, who apply chemical treatments each year to limit its impact on rice yield and milling quality. Good agronomic practices such as varietal choice and reduced nitrogen fertilization can also be effective in limiting the impact of the disease, which largely varies across sites and growing seasons. Here we present a three-year experiment (2013–2015), in which blast disease severity was dynamically sampled on four varieties grown with two nitrogen doses (standard and double farmer fertilization) in three sites located in Northern Italy (i.e., the largest European rice district). No chemical treatments were applied on these experimental plots, which were compared to blast-treated controls. Field yield and yield after milling (t ha−1) were measured to assess the impact of rice blast. Disease progress curves of leaf and panicle blast were analyzed via F-test for site, nitrogen dose, rice variety, and year. The areas under disease progress curves were correlated with yield losses via linear regression. Finally, a 4-way analysis of variance was performed using field yield losses and head rice yield as dependent variables. Results Blast epidemics were significantly affected by all the factors considered, with rice variety and year as the most important sources of variability. Areas under disease progress curves were significantly correlated with losses in field yield and even more in yield after milling, with panicle blast proving to be the most impactful symptomatology. Year and variety ranked first and second among the factors explaining yield losses, both in field and after milling. These results confirm the effectiveness of varietal choice to reduce blast impact, indicating that fungicide applications should be conditional to the conduciveness of weather conditions.