Photosynthesis in rust-infected adult Norway spruce in the field.

•  Norway spruce (Picea abies) has been infected by the needle rust Chrysomyxa rhododendri in many regions of the Central Alps with increasing intensities in recent years. Basidiospores formed on leaves of the main host, Rhododendron sp., only penetrate into developing current-year needles of Norway spruce, which leads to shedding of infected needles in the autumn.