Alternate host screening of Thekopsora areolata in Scandinavia: a new record on Prunus grayana

Abstract

The cherry spruce rust caused by Thekopsora areolata results in significant losses in spruce seed production in forest industry. The pathogen is present in Asia and Europe but absent from North America where it has been considered as a potential threat and listed as a quarantine organism by the USDA. A comprehensive list and in-depth information regarding the alternate hosts of this pathogen is important for conducting epidemiological studies and for optimal disease control. Prunus padus is the main alternate host reported for T. areolata. In this study, we investigated the susceptibility of domestic and exotic Prunus spp. and other potential alternate host plant species native to Scandinavia, to T. areolata infection, through a field survey and aeciospore inoculation experiments in the greenhouse and laboratory. No new susceptible species were found. In Sweden, a new record of P. grayana with low susceptibility to T. areolata was found. In addition, we updated the list of currently confirmed alternate hosts of T. areolata according to field observations and inoculation results. Prunus padus, P. serotina, and their hybrids, as well as the subspecies of P. padus are highly susceptible, while P. depressa, P. grayana, P. spinosa, and P. tenella are considered slightly susceptible.