Infection of Norway spruce container seedlings by Gremmeniella abietina
First- and second-year containerized Norway spruce seedlings were inoculated with conidia of type A (large tree type) and type B (small tree type) of Gremmeniella abietina var. abietina at different times during the summer. The appearance of symptoms after artificial inoculation and natural infection on spruce seedlings were recorded the following spring and compared with the disease symptoms on Scots pine seedlings. The proportion of diseased seedlings after inoculation reached as high as 80%. The susceptible period during the summer began later on the first-year seedlings than on the second-year seedlings, and was similar for the pine seedlings. Susceptibility of first-year seedlings was highest in August and on second-year seedlings in July. The accumulated temperature sum, relative humidity and height growth for first- and second-year seedlings was assessed. Natural infection in 2002 caused more disease on pine than on spruce seedlings. Experimental thinning of seedlings had no effect on disease incidence.
In a preliminary comparison between the ability of A and B types to cause disease in Norway spruce seedlings, type B caused more damage than type A after inoculation. However, type A caused a high disease frequency in other experiments in this study.
Symptoms on Norway spruce seedlings often first occurred in the mid-section of the shoot, and were similar to those observed on pine seedlings: needles turned brown, starting at the needle base, in the spring following inoculation. On first-year spruce, diseased needles were shed rapidly, in contrast to a slower rate of shedding on first-year pine seedlings. Pycnidia developed about 2 years after inoculation (on pine 1 year after inoculation). On Norway spruce seedlings the lower part of the shoot, including the lateral shoots, often remained alive.
The experiments show that G. abietina can cause disease on containerized Norway spruce seedlings under nursery conditions in Finland. The coincidence of spore dispersal, seedling susceptibility and predisposing factors are important in disease development.
Document Type: Research Article
Publication date: 2008-02-01