Methyl jasmonate and oxalic acid treatment of Norway spruce: anatomically based defense responses and increased resistance
against fungal infection
Paal Krokene (1, 2), Nina Elisabeth Nagy (1) and Halvor Solheim (1)
1. Norwegian Forest and Landscape Institute, P.O. Box 155, 1431 Ås, Norway / 2. Corresponding author () / Received March 13, 2007; accepted May 24, 2007; published online October 15, 2007
Summary
To study the effect of chemical pretreatment on conifer resistance, 13-year-old Norway spruce (Picea abies (L.) Karst.) trees were treated with methyl jasmonate (MJ) or oxalic acid (OxA) on the outer bark and inoculated with the
pathogenic blue-stain fungus Ceratocystis polonica (Siem.) C. Moreau 4 weeks later. Both chemicals significantly reduced symptoms of fungal infection, but MJ was more effective
than OxA (51 versus 18% reduction in length of necrotic lesions in the phloem relative to untreated control trees). Anatomical
examination of treated stem tissues showed that MJ induced extensive formation of traumatic resin ducts in the xylem and extra
polyphenolic parenchyma (PP) cells in the secondary phloem between the cambium and the regular annual PP cell layer. No traumatic
resin ducts were formed after treatment with OxA, and the coverage of extra PP cells in OxA-treated tissues was not significantly
higher than in the controls. The anatomically based defense reactions induced by MJ were similar to the reactions observed
after pathogen infection, mechanical wounding and bark beetle attack. Neither MJ nor OxA had apparent phytotoxic effects on
Norway spruce at the concentrations used, with needle and stem tissues of all trees appearing normal without visible symptoms
of toxicity. However, trees treated with MJ had 30% less radial sapwood growth than control trees. In conclusion, MJ treatment
of Norway spruce appears to have practical potential as a tool for increasing plant resistance to fungal infection, but with
a modest reduction in sapwood growth.
