Diseases and disorders on fir (Abies spp.) grown as Christmas trees, boughs, and landscape plants in Norway; from seed to site.
In Norway, true fir (Abies spp.) is mainly grown for ornamental purposes, with Christmas trees as the most important product. Nordmann fir (A. nordmanniana) and subalpine fir (A. lasiocarpa) are the dominant Christmas tree species, and noble fir (A. procera) the dominant bough species. In landscape, white fir (A. concolor) and Korean fir (A. koreana) are the most commonly planted fir species. A number of pathogens may cause diseases on true fir in nurseries, forest stands, Christmas tree fields, bough plantations, and landscape plantings around the world. Both root and butt rots caused by soilborne pathogens, and foliage, shoot and stem diseases caused by airborne pathogens are common. No fir species are native to Norway. With the import of seeds and transplants, a number of disease-causing fungi and Phytophthora spp. were introduced. From 2000-2008 we analyzed hundreds of diseased firs from many locations in southern Norway, and revealed a number of disease-causing organisms (Paper I). The most serious diseases in bough and Christmas tree fields were Phytophthora root rot on noble, Nordmann, and subalpine fir, and Current Season Needle Necrosis (CSNN) on Nordmann fir. On white fir in landscape plantings a Neonectria-epidemic damaged and killed a lot of trees. Hence, Phytophthora spp. (Paper II & III), Neonectria spp. (Paper IV), and CSNN (Paper VI & VII) were subject for further investigations. Phytophthora cambivora was isolated from severely damaged noble fir in a bough plantation. Approximately 25% of the 15-year-old trees were dead or dying. Inoculation tests were carried out and pathogenicity confirmed (Paper II). A Phytophthora similar to P. inundata was isolated from Nordmann fir Christmas trees in one plantation. Around 70% of trees were dead one year after planting. From 7-year-old subalpine fir Christmas trees, Phytophthora megasperma was isolated. Approximately 25% of trees had severe symptoms. Koch's postulates were fulfilled for both Phytophthora spp. from the Christmas tree fields (Paper III). The same Neonectria sp. found on white fir was also isolated from subalpine fir, Siberian fir (A. sibirica) and Norway spruce (Picea abies). Isolates obtained were compared to N. fuckeliana isolates from Norway spruce in Finland, and found to be morphologically different. The difference was shown by sequencing of the ITS regions of the rDNA. The Norwegian isolates were 5 base pairs different from the Finnish, and the domestic isolates may turn out to be a new species. In pathogenicity tests, isolates from both countries proved pathogenic (Paper IV). We investigated if any of the diseases we had found could possibly be seedborne (Paper V). Among several other potential disease causing fungi, we found Sydowia polyspora on seeds from Nordmann fir, noble, and subalpine fir. This was a very interesting finding, because S. polyspora was later associated with CSNN. CSNN is a major disease on fir both in USA and Europe, and yearly losses are considerable on both continents. New needles turn chlorotic a few weeks after bud break. The chlorotic areas turn necrotic during the summer and the damage may result in heavy needle cast. There were indications from research in USA that the cause of CSNN was lack of calcium (Ca). Hence, we performed a greenhouse study with Nordmann fir transplants grown in chelator buffered nutrient solution with an suboptimal level of Ca. No CSNN symptoms were obtained. The greenhouse study was compared to nutritional status from field observations (Paper VI). Further we investigated if CSNN possibly was caused by a fungal infection. This had been suggested from different countries, but not proved by pathogenicity tests. We obtained CSNN symptoms by inoculating seedlings and transplants with S. polyspora (Paper VII).