Fungal injury to seed tissues of Norway spruce, Picea abies (L.) Karst.

Norway spruce bore an abundance of cones in Finland in 2000, but these cones were often fungal-infected. The seeds had structural injuries that were revealed when seed samples were examined using light (LM) and a field emission scanning electron microscope (FESEM). Two main types of spores were found either in the tissues inside the seed coat or on the sarcotesta, the outermost layer of seed coat. The spores of Chrysomyxa pirolata appeared particularly in the nucellar tissue, where the cell walls were disintegrated at the middle lamellae and cytoplasm was disrupted. Degenerated remnants of fungal structures resembling aecial peridium were found close to aeciospores. The tissue of the megagametophyte differed also from that of a normal mature seed. Conidia of Thysanophora penicillioides were often encountered on the sarcotesta where the ordinary wax cover was missing. Fungal injury occurred in the nucellar layers that shelter the embryo and megagametophyte from desiccation and oxidation. Destruction of these structures together with rapid opening of the seed coat advance deterioration of seeds during storage and may cause unexpected economic losses in forest plant production.