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 suscepti ble after mass inoculations of Letographium wingfieldii, a fungus associate d with Tomericus piniperda, were submitted to a low density of fungal inocu lations or beetle insertions. The length of the phloem-induced reaction zon e, the fungal extension and fungal density inside the reaction zone, and th e 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 p hloem, and the length of the maternal galleries in the reaction zone were h igher in the susceptible trees than in the resistant ones. These factors co uld be good indicators of resistance of Scots pine to mass attacks.