Monoterpenes as potential markers for relative susceptibility of Sitka spruce to Heterobasidion annosum

Lesions lengths were measured on inner bark of 2 year old clones of Picea sitchensis 35 days after inoculation with Heterobasidion annosum. Monoterpene responses were compared in 2 clones with short lesions (less susceptible) and 2 with long lesions (more susceptible). Less susceptible clones had higher proportions of (+)-?-pinene, (-)-?-pinene and unknown terpene 15 in constitutive resin, whereas more susceptible clones had higher amounts of (-)-limonene, and 3 unknowns. In secondary resin produced around lesions there was a decrease in -phellandrene and corresponding small increases in certain minor terpenes. Amounts of most monoterpenes increased in infected tissues. Inoculation with H. annosum resulted in an increase in unknown 19, whereas in more susceptible clones, concentrations of ?-3-carene and unknowns 13 and 16 increased. Differences in both constitutive and induced resin monoterpene profiles may provide useful markers for resistance to H. annosum for use in selection programmes.