Inter-tree variability in the induced defense reaction of Scots pine to single inoculations by Ophiostoma brunneo-ciliatum, a bark-beetle-associated fungus

Abstract

In 1987 and 1988, 100 trees year −1 were characterized by their age, height, diameter, area of sapwood section at breast height and growth efficiency indices. At different periods in the year, they were each inoculated with Ophiostoma brunneo-ciliatum at two diametrically opposite locations on the bole. The characteristics of the induced defense reactions (length of reaction zone and total resin quantity) were read in the phloem. The defense reaction zones of old trees (75–115 years old) always contained a greater total quantity of induced resin than the young trees (27–40 years old). They were also longer than in the young trees in 1987. The length of the reaction zone was smaller in June than later in the year, but the quantity of resin remained the same. Growth efficiency was always negatively correlated with the length of the reaction zone, but its correlation with the total quantity of resin in the young trees varied according to the year. In the young trees, total resin quantity was always positively correlated with tree diameter and area of sapwood section. The results are discussed in relation to the resources involved in the tree's induced response and with the levels of attack density thresholds above which the tree's defense is overcome. It is suggested that these resources are mainly current photosynthates in the case of young trees, while they could be otherwise in the case of old trees. It is pointed out that whilst there is undoubtedly a relationship between single reactions to individual attacks and growth efficiency, the low correlation coefficients do not allow the conclusion that lesion length or total resin from this reaction can be used as indices of the tree's defense capability.