Abstract
Abstract Epidemics of Scots pine blister rust, caused by Cronartium pini, have become an increasing problem in northern Finland and Sweden. The biology of the rust fungus is complex, with two different life cycle forms that cannot be morphologically distinguished, and it is unclear to what extent the two forms contribute to the epidemics. Genetic structure of fourteen populations of C. pini were investigated in Fennoscandia. Distinction between the two life cycle forms, a heteroecious and an autoecious one, was made by determining zygosity using microsatellite markers, and AFLP markers were developed to analyse population genetic relationships. The results showed that the two life cycle forms are clearly differentiated and occur in separate populations. Within the life cycle forms, geographic differentiation was evident, probably due to restricted gene flow as well as connection with different alternating hosts. The host-alternating form dominated in the epidemic regions in northern Fennoscandia. Implications for silvicultural practices are discussed.
Highlights
IntroductionEpidemics of Scots pine blister rust (or resin-top disease), caused by the rust fungus Cronartium pini
Epidemics of Scots pine blister rust, caused by the rust fungus Cronartium pini
When variation between life cycle forms were included in a three-level Analysis of Molecular Variance (AMOVA), the analysis showed that 13% of the variation was attributed to variation between the two forms and 13% of the variation among populations within the forms (Table 4)
Summary
Epidemics of Scots pine blister rust (or resin-top disease), caused by the rust fungus Cronartium pini Cronartium flaccidum, Peridermium pini) have resulted in serious damage of young Scots pine (Pinus sylvestris) forests in northern Finland and Sweden in the last decades (Kaitera 2000; Wulff et al, 2012; Skytta€ 2017). Based on the 7th Finnish NFI (National Forest Inventory), 2.55% of mature Scots pines especially in nutrient-rich and dry soils were infected in northern Finland in the early 1980s (Kaitera and Jalkanen 1995). The epidemics have been severe in western Lapland and expanded southwards to Northern Ostrobothnia. An inventory in Sweden in 2008 showed that 130,000 ha, or 34% of young pine forests, were infected in the counties Norrbotten and V€asterbotten (Wulff et al, 2012), and C. pini was determined as dominant cause of forest damage in the region of Norrbotten in 2019 (Normark 2019).
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