Host resistance to the fir engraver beetle. 3. Lesion development and containment of infection by resistant Abies grandis inoculated with Trichosporium symbioticum

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Abstract
Development of lesions in resistant grand fir trees was observed from time of uninoculated- control injury and Trichosporium symbioticum inoculation to wound stabilization. Lesion development was similar in both types of injury, showing a rapid expansion phase followed by expansion reduction and stabilization. However, in fungus-inoculated wounds vertical lesion growth in the first 7days was much more rapid.Microscopic examination and culturing data showed that T. symbioticum generally lags behind the lesion boundary and is confined within the lesion at the time of wound stabilization. Schizogenic traumatic resin cavity formation begins 14–21 days after wounding and is followed by callus formation 14 days later.Reisolation of the fungus from the lesion indicated that resin and phenolic compounds which accumulated within the reaction zone had little effect on the viability or virulence of the pathogen. These results suggest that fungal confinement in the lesion in resistant grand fir is due to degenerative metabolism within the lesion, which robs the medium of nutrients essential to fungal growth and development, and later is due to secondary resin produced by traumatic resin cavities.