Open access publications in the SLU publication database

Abstract

Sweden is one of the top five countries having large planted forest areas, and here the forests are maintained by clear-cut regime, which also promotes the pine weevil (Hylobius abietis), a major threat to Swedish planted coniferous regeneration. Given interest in developing sustainable forest management practices, efficient non-insecticide alternatives are highly demanded to tackle the pine weevil problem. In this thesis, I investigated several potential measures, based on plant defenses, aimed at reducing pine weevil damage to conifer seedlings. Methyl jasmonate (MeJA) is a plant hormone that can trigger plant induced defense/resistance, and reduce pest insect damage in conifers. I examined the compatibility of MeJA treatment with current plant nursery practices, and explored if inflicting mechanical damage can also trigger induced resistance. I also investigated if the timing of MeJA treatment will affect bark wound healing as a plant tolerance trait. I further examined genetic variation in resistance to weevil damage among different families from the Swedish breeding program, and resistance differences between two types of planting materials, seedlings and cuttings. The results confirmed that seedlings exhibit greater resistance to weevil damage when treated with MeJA, even if treatment is applied the previous growing season. In contrast, the evaluated mechanical damage did not trigger strong induced resistance in seedlings. Moreover, if MeJA treatment occurs after seedlings are wounded, healing of bark wounds can be negatively affected, but not if the treatment occurs before wounding. In addition, I found that seedling’s resistance to pine weevil damage is significantly different among families, but the heritabilities of resistance traits were low and may constrain breeding for more resistant seedlings. When examining plant types, cuttings showed higher resistance to pine weevil damage than seedlings from the same family. Further studies should examine the interaction of MeJA-induced seedlings with abiotic and biotic factors under field conditions. The combination of induced resistance with constitutive resistance will also be necessary to fully exploit plant defenses in plant protection.