Kaitera, J., Tillman-Sutela, E. and Kauppi, A. 2009. Cone Bagging Hinders Cone and Rust Development of Picea abies Baltic Forestry 15 (1): 28-32

Fruiting and sporulation of Norway spruce cone rusts were investigated in northern Finland. Pistillate flowers and developing cones were bagged at three intervals during the growing season to hinder cone infection by cone rusts, Thekopsora areolata and Chrysomyxa pirolata. The bagging of cones hindered the maturation and sporulation of T. areolata aecia in pistillate cones covered in May, although it also significantly retarded the development of these cones. The bagging fully restricted the formation of C. pirolata fruitbodies in cones. The amount of infected cones, however, was very small in general, regardless of the coverage of cones or lack of it during the growing period. In October 40 % of the unbagged cones bore T. areolata aecia and 7 % C. pirolata aecia. All of the unbagged cones developed normally and the rusts in the infected ones sporulated. Insects were more significant and common than rusts in 2007. The results indicated that rust colonization and fruiting are greatly dependent on the undisturbed development of spruce cones. The total lacking of T. areolata spermogonia in the infected cones implies that rust infection process can occur even without basidiospores. The small amount of cone scales bearing fruitbodies of both of the rust species suggests that they hinder the spread of infection of one another in the same cones.

Key words: cherry spruce rust, Chrysomyxa pirolata, cone rusts, inland spruce cone rust, Thekopsora areolata, Norway spruce