Chrysomyxa rhododendri in Trentino: a first analysis of monitoring data

Chrysomyxa rhododendri de Bary is a well-known pathogen that frequently produces massive and conspicuous attacks on Picea abies Karst. in the Alps. Although the cycle of this rust was described at the end of the 19th century, it is only recently that research has focussed on its real impact on spruce dynamics at the treeline. In Trentino, spruce needle rust is regularly reported through the Forest Tree Damage Monitoring (FTDM) programme, carried out by FEM-IASMA and the Forest and Fauna Service in the woodlands of the Autonomous Province of Trento (N.E. Italy). This set of geographically referred data was analysed and correlated with meteorological and ecological parameters in order to gain a better understanding of the environmental factors involved in attacks of this rust. Measures taken from representative meteorological stations and data from woodland management plans were also analysed. Rust infections were reported during every year of the period studied, but with considerable variability in terms of both affected surface and spatial distribution, although no clear trend was observed over the whole period. This variability could be explained by variations in precipitation in May and June, which is known to be the period of basidiospore release; solar radiation and wind could concur in spreading the fungal attack. Other parameters played a less important role in explaining the spread of rust, which affected all kind of spruce woods, regardless of age and management. Local morphology seems to be a significant factor in spreading attacks. FDTM data showed high potential for obtaining a better understanding of spruce rust behaviour