Influence of fungal infection and wounding on contents and enantiomeric compositions of monoterpenes in phloem of Pinus sylvestris

To identify chemical resistant markers induced by fungal or mechanical injury, young trees of Scots pine (Pinus sylvestris) were subjected to inoculations of blue stain fungi associated with the pine shoot beetles Tomicus piniperda and T. minor. Among the 20 trees selected for chemical analyses, 16 were divided into four groups: one as control and three were pretreated by wounding only, or by inoculation with either the blue stain fungus Leptographium wingfieldii or Ophiostoma canum. Four wk after pretreatment, all 16 pretreated trees were mass-inoculated with L. wingfieldii. The absolute and relative amounts, as well as the enantiomeric compositions of monoterpene hydrocarbons in the phloem, were determined via a small sample of the phloem before and after the pretreatment and mass inoculation, by using two-dimensional gas chromatography (2D GC) and GC-mass spectrometry (MS). After mass inoculation, the absolute amounts of most of the monoterpenes decreased in the phloem sampled > 20 cm from the fungal infection, and were higher in the phloem sampled within the infected reaction zone. The relative amounts of both (-)-beta-pinene and (-)-limonene increased in phloem samples taken > 20 cm above the fungal inoculation in the preinoculated trees compared with phloem sampled from the remaining four control trees. The enantiomeric compositions of beta-pinene and limonene changed, after fungal growth, at defined distances from the inoculation site: the proportion of the (-)-enantiomers was highest in the phloem sampled > 20 cm from the fungal inoculation. Four wk after pretreatment, monoterpene production in the phloem at the site of inoculation was more enhanced by L. wingfieldii than by O. canum. However, the different virulence levels of the fungi did not affect the enantiomeric composition of the monoterpenes. The biosynthesis of monoterpene enantiomers is discussed in relation to induced pathogen resistance.