Effects of Seasonality and Climate on the Propagule Deposition Patterns of the Chestnut Blight Pathogen Cryphonectria parasitica in Orchards of the Alpine District of North Western Italy

Chestnut blight is the major disease of chestnuts (Castanea spp.) cultivated worldwide for the production of edible nuts. The disease is caused by the pathogenic fungus Cryphonectria parasitica, which infects trees by means of airborne propagules penetrating through fresh wounds on stems and branches. The aims of this study were to (I) assess the temporal propagule deposition patterns of C. parasitica in the Alpine district of North Western Italy, (II) test and model the effects of seasonality and climate on the above patterns, and (III) investigate the spatial distribution of propagule deposition at the within-site scale. A two-year-long spore trapping experiment was conducted in three chestnut orchards. Approximately 1300 samples were collected and processed with a species-specific qPCR assay to quantitatively assess the propagule deposition of C. parasitica. Results showed that C. parasitica can release propagules all over the year, though with significant seasonal peaks in the spring and fall (p < 0.05). Large propagule loads were significantly correlated (p < 0.05) with an increasing number of rainy days of the week (days providing 1-10 mm/day of water). Models predicting periods at high risk of infection based on climate and seasonality were fitted and successfully validated (p < 0.05).