Thekopsora and Chrysomyxa cone rusts damage Norway spruce cones after a good cone crop in Finland

Abstract

In 2006, an excellent crop of Norway spruce [Picea abies (L.) Karst] cones in Finland was severely damaged by rust fungi. The distribution and frequency of infection and the fruiting and sporulation of these rusts were investigated in 9 seed orchards and 23 seed tree stands in Finland. Thekopsora areolata (Fr.) Magnus was the most common and important cone rust that significantly reduced the seed crop of orchards in southern Finland, where infections were 10–89%. In northern Finland, the frequency of infected cones was much lower in seed tree stands (0–10%) than in seed orchards. Chrysomyxa pirolata Wint. occurred less frequently in most stands, but was more common in seed orchards. Chrysomyxa ledi (Alb. & Schw.) de Bary was the most frequent cone rust in seed tree stands of northern Finland. Thekopsora areolata colonized most or all of a cone and formed aecia on both adaxial and abaxial scales, while cone infections of C. pirolata were incomplete and sporulation took place only on the abaxial scale surface, as did C. ledi. Thekopsora areolata aecia failed to sporulate during the first year of cone formation, while aecia of both C. pirolata and C. ledi sporulated. Seed formation was significantly hampered and the seed crop significantly reduced by both T. areolata and C. pirolata.

Keywords:

• Chrysomyxa ledi
• Chrysomyxa pirolata
• Picea abies
• seed orchard
• sporulation
• Thekopsora areolata

Acknowledgements

I thank Mr. Timo Ari and the field staff of the Finnish Forest and Park Service for delivering cones from northern Finland, and Dr. Tiina Ylioja and the staff of Siemen-Forelia and Tapio for the cones from southern Finland. Ms. Irene Murtovaara prepared the figure and Dr. Michael Hardman checked the language.