Chrysomyxa ledi, a new rust fungus sporulating in cone scales of Picea abies in Finland

Seasonal fruiting and sporulation of cone rusts were investigated in Norway spruce cones during the growing season of 2007, a year after an excellent cone crop and a severe outbreak of rust. Current-year and 1-year-old cones were collected bimonthly to monthly from case-stands in southern and northern Finland and checked for rust fruitbodies. A previously unreported species of rust formed spermogonia and aecia, and sporulated on the cone scales of Norway spruce in two study areas. Morphologically, the rust was distinct from other spruce cone rusts and, based on ultrastructure of aecia and aeciospores, most closely resembled Chrysomyxa ledi. Molecular analysis of the aeciospores confirmed that the rust belonged to the C. ledi/C. rhododendri complex. The rust fruited frequently but only colonized a few scales per cone and presumably had a minor effect on cone development and seed crop.