Pathogenicity of Thekopsora areolata from seed orchards in Finland on Prunus spp. and Picea abies

Abstract

Pathogenicity of cherry‐spruce rust, Thekopsora areolata, was investigated by inoculations with aeciospores from seven Norway spruce, Picea abies, seed orchards that had suffered from successive severe rust epidemics in the 2000s in Finland. Detached leaves of Prunus spp. were inoculated in the laboratory using aeciospores from cones of various ages. In the greenhouse, live Prunus padus plants were inoculated, and possible autoecism of the rust was tested by inoculations of Picea abies seedlings. Thirty‐five spore sources from the seed orchards formed uredinia on Prunus spp. in the laboratory 2 weeks after incubation, but no telia developed. In the greenhouse, uredinia developed on live P. padus, but no rust symptoms, cankers or sporulation were detected on Picea abies. Thus, no evidence of autoecism was observed among the T. areolata populations and therefore all populations, suggesting all those tested from the Finnish seed orchards were heteroecious.

Temperature range for germination of <i>Thekopsora areolata</i> aeciospores from Finnish Norway spruce seed orchards

“…This is clearly an advantage for the rust as it is able to infect and germinate on alternate hosts in the early spring as their leaves develop. Formation of uredinia within 10-14 days on aeciospore infected young Prunus leaves was recently shown by artificial inoculations (Kaitera et al 2019). The first uredinia develop on Prunus in late May on natural plants in seed orchards in Finland (Kaitera, unpublished).…”

“…Some of these cones may contain viable spores for years after initial formation as was shown by Kaitera and Tillman-Sutela (2014). Also infected cones that fall down may contain viable spores, but their germination rate is lower than in most cones that remain in the trees (Kaitera et al 2019). The temperature curve of germination, however, is similar regardless of the spore source as shown in this study.…”

“…All seven cones represented different rust populations, but we did not identify spores from the cones genetically in this study. However, in another study, a total of 35 cones from the same rust populations as in this study were used in Prunus inoculations, where the rust populations were identified genetically as T. areolata (Kaitera et al 2019).…”

“…The main alternate hosts of T. areolata are Prunus spp. (Gäumann 1959;Kaitera et al , 2019. Recently, T. areolata was shown to be heteroecious without an ability to spread from Picea to Picea (Kaitera et al 2019).…”

“…(Gäumann 1959;Kaitera et al , 2019. Recently, T. areolata was shown to be heteroecious without an ability to spread from Picea to Picea (Kaitera et al 2019). The aeciospores of the rust are viable from aecia of old infected cones for years (Kaitera and Tillman-Sutela 2014), which is beneficial for the rust to survive over unfavourable seasons and to infect Prunus for a long time.…”