Coupling a generic disease model to the WARM rice simulator to assess leaf and panicle blast impacts in a temperate climate

Blast disease (Magnaporthe oryzae B. Couch) is one of the most important causes of rice yield losses worldwide. Although farmers implement countermeasures to limit its impacts, blast disease is still an important constraint to rice production in both tropical and temperate environments. This study presents the coupling of a generic disease model to the WARM rice simulator to quantify the pathogen impact on key physiological processes and thus on final yield. The impact of leaf blast was simulated by reducing the photosynthetic leaf area index and in turn radiation interception, as a function of disease progress rate. Panicle blast damage was reproduced by decreasing the percentage of photosynthates translocated to kernels. The modelling solution was calibrated and evaluated using field observations of blast impact at harvest, collected on 20 rice cultivars with different blast resistance and grown in five sites in Northern Italy in the period 1996-2012 (total 272 observations). Results showed a good correlation between simulated impacts (fraction of potential yield) and observations (0-5 scale used for the visual assessment, with 0 = no impact and 5 = complete crop failure), for both calibration (R2 = 0.57) and evaluation (R2 = 0.51) datasets. Model outputs were converted to the same scale used for the visual assessments to perform an in-depth evaluation of the modelling solution, which exactly matched the 46% of observed impact values, and presented an error of 1 class in 48.2% of the cases. This study demonstrated the soundness of the approach developed for crop-pathogen interactions and its suitability for the application in research-e.g., to explore the impacts of climate change on blast-related yield losses -and operational contexts-e.g., to test alternate fungicide strategies to optimize agricultural chemical applications.