Genetic diversity and bark physiology of the European beech (Fagus sylvatica): a coevolutionary relationship with the beech scale (Cryptococcus fagisuga)

In 1994 and 1995, the degree of infestation by the beech scale (Cryptococcu s fagisuga Lind.) was recorded on 120 beech trees (Fagus sylvatica L.) in t he Pless Forest near Gottingen, Germany. Simultaneously, the trees were cha racterized genetically and compounds of primary and secondary metabolism of beech bark were analyzed. A correlation was established between beech scal e infestation and the genotype of the host trees, based on gene locus A of isocitrate dehydrogenase (IDH-A). The fraction of infested beech trees was higher in the heterozygous genotype A2A3 group than in the homozygous genot ype A2A2 and A3A3 groups, whereas the fraction of beech trees with decreasi ng infestation from one year to the next was lower in the heterozygous geno type A2A3 group than in the homozygous genotype A2A2 and A3A3 groups. Concentrations of soluble carbohydrates, protein amino acids and proanthocy anidins were determined in the inner and outer bark of trees with differing degrees of infestation. The results indicate that the defense reaction of beech against infestation by beech scale comprises multiple processes in wh ich nutrient availability to the beech scale is reduced by concentration sh ifts and by the formation of inhibiting compounds.