Effekten av metyljasmonat som skydd mot gnag av snytbagge (Hylobius abietis) på gran- och tallplantor

Abstract: The effect of methyl jasmonate on resistance against the large pine weevil (Hylobius abietis) in Scots pine and Norway spruce seedlings. A field experiment was conducted in order to determine the dose-response effects of methyl jasmonate (MJ) on growth and defence to pine weevils in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) and to compare the effect of MJ between pine and spruce. In addition a complementary greenhouse experiment was conducted with the same aims as above and to determine the amount of resin ducts and their correlation to the feeding of pine weevils. The field experiment was conducted on a fresh clear cutting in Garpenberg, southern Dalarna in central Sweden. The experiment consisted of 30 blocks with three kinds of containerized seedlings: 2-year old spruce, small pine (before shoot elongation) and 1-year old pine (already shoot elongated). They were all exposed to 4 treatments 14 days prior to the experiment: control, 25 mM/L MJ, 50 mM/L MJ and 100 mM/L MJ. Data on weevil damage and seedling growth were collected after the first and the second growing season. The seedlings in the greenhouse experiment were of the same kind and were exposed to the same treatment as the ones in the field experiment. Three cages (size ca 1,5 m2) were used; one for each kind of seedlings, and each contained all 4 treatments with 6 replicates (four replicates for the small pine). One weevil per seedling was released in each cage, and the study was interrupted after 1-6 weeks depending on the feeding activity of the weevils. The growth data from the field experiment was subjected to ANOVA's (GLM). The first growing season (2004) there was no block effect for either length growth or diameter. There was a significant difference between treatments for diameter but not for length. There were significant differences between the kind of seedling for both length and diameter. The second growing season (2005) there was a block effect. There was a significant difference between treatments and the different kind of seedlings for length growth but not for diameter growth. Thus, the results show that growth was significantly reduced by the MJ-treatment. The gnawing data from the field experiment were subjected to a non parametric Kruskal-Wallis test. There were no significant differences between the treatments in any of the tested seedling types, in none of the seasons. The data from the greenhouse experiment were subjected to One-way ANOVA's and regression analysis. There were strong significant differences between treatments in the number of resin ducts for all of the plant types. There was no significant difference in the area of gnawing between treatments. There was no significant correlation between gnawed areas and the number or area of resin ducts. However there was a tendency for the spruce and 1-year old pine that increasing amount of resin ducts led to decreasing amount of feeding by pine weevils. In conclusion the MJ-treatment leads to reduced growth and increasing numbers of resin ducts but no additional protection against the large pine weevil. The timing and concentration of MJ is crucial for the effect of the treatment.