Phenology of rust fungi (Pucciniales) during mild winters – high temporal flexibility of spore generations

Rust fungi develop up to five spore generations that often infect host plants of two different families in one life cycle. We investigated the phenology of spore generations over winter by monitoring rust infections over ten years in urban, wild vegetation in Western Germany. We obtained 1177 records of plants infected by 33 species of rust fungi. We observed basidia (mostly inferred from empty teliospores), spermogonia, and aecia mostly during spring, maximum development of urediniospores during summer and of telia in autumn and winter. Surprisingly, during winter months with mild temperatures, newly developed urediniospores on perennial hosts were frequently found, sometimes showing massive growth. Other spore generations also sporadically occurred at unusual times of the year. By their high number and diversity of spore generations as well as great phenological flexibility, rust fungi probably easily adapt to changing weather conditions.