Cherry spruce rust in the Wigry National Park and Suwałki Forest District: cone infestation and its implications

Thekopsora areolata and Chrysomyxa pirolata are pathogens preferentially infesting Norway spruce cones and lead to the complete failure of spruce seed yield. Thus, the presence of seed-injuring pathogens may be a crucial factor driving close association between cherry spruce rust occurrence on trees and limited natural regeneration of the preferred host. However, a major uncertainty remains as to which pathogens are responsible for cone infection and reduced seed viability, resulting in impeded renewal of young trees. Our study aims to investigate whether T. areolata or C. pirolata presence on the Norway spruce cones was responsible for cherry spruce rust in three sites within the Wigry National Park (one site) and the Suwałki Forest District (two sites) in North-Eastern Poland. We harvested randomly five infested Norway spruce cones from each location and analysed them to verify specific pathogen occurrence. We analysed rDNA fragments such as ITS regions and 28S to precisely identify the disease causal agent on the cones and estimate the potential of genetic diversity of the analysed fungus species. Thekopsora areolata was identified as the main fungus promoting cherry spruce rust, suggesting that host species regeneration is constrained by this pathogen’s distribution. We assumed that the apparent cherry spruce rust presence and lack of Norway spruce natural regeneration likely result from cone infection and the availability of healthy, high-quality seeds. Moreover, the occurrence of cherry spruce rust may explain the challenges associated with the deficit of seeds used for the artificial regeneration of spruce stands.