Resistance level in Scots pine clones and artificial introductions of Tomicus piniperda (Col., Scolytidae) and Leptographium wingfieldii (Deuteromycetes)

Scots pine trees belonging to clones considered to be resistant or susceptible after mass inoculations of Leptographium wingfieldii, a fungus associated with Tomericus piniperda, were submitted to a low density of fungal inoculations or beetle insertions. The length of the phloem‐induced reaction zone, the fungal extension and fungal density inside the reaction zone, and the length of maternal galleries of T. piniperda were measured. The length of the phloem reaction zone never differed between resistant and susceptible trees. The density of the fungus mycelium in histological sections of the phloem, and the length of the maternal galleries in the reaction zone were higher in the susceptible trees than in the resistant ones. These factors could be good indicators of resistance of Scots pine to mass attacks.