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CAN PHLOEM PHENOLS BE USED AS MARKERS OF SCOTS PINE
RESISTANCE TO BARK BEETLES?
F. LIEUTIER _,F. BRIGNOLAS l, V. PICRON t, A. YART l, and C. BASTIEN 2
tStation de Zoologie Foresti_re, Institut National de la Recherche Agronomique
Ardon, 45 160 Olivet, France
2Station d'Am61ioration des Arbres Forestiers, Institut National de la Recherche Agronomique
Ardon, 45 160 Olivet, France
INTRODUCTION
Bark beetle damage is considerable in all coniferous forests in the temperate zone. In most cases, it results from
beetle attacks surpassing the critical density (numbers/m 2)below which trees can successfully reject them. Above this
threshold, natural mechanisms of tree resistance are overcome by the beetles and fungi which become successfully established.
The level of this critical threshold of attack density is a fundamental expression of the strength or capacity of tree
resistance (Berryman 1978, 1982; Christiansen et al. 1987).
The basic phenomenon involved in the resistance is a phloem reaction induced by the invaders and localized around
them. It consists of a rapid synthesis of chemicals, including secondary metabolites such as terpenes and phenols, which
impregnate tree tissues (Reid et al. 1967, Berryman 1972, Shrimpton 1973, Christiansen and Horntvedt 1983, Christiansen et
al. 1987, Lieutier et al. 1988, Lfmgstr6m et al. 1992, Lieutier 1993). The critical threshold of attack density depends on the
quantity of energy the tree is able to rapidly mobilize for various syntheses in the reaction zones, and this quantity is necessarily
limited (Christiansen et al. 1987). Thus, the threshold can be high if the lag time for stopping an aggressor at each
point of attack is very short and hence the energy mobilized for that purpose in each reaction zone is low. Under these
conditions of arrested attacks, a short reaction zone has been assumed to be more effective than an extended one (Lieutier et
al. 1993).
Markers of conifer resistance to bark beetles could be very useful; e.g., forecasting susceptibility to beetle attacks and
beetle outbreaks, and aiding in selection of highly resistant trees. Because the concentrations of secondary metabolites vary
considerably during tree responses to aggression, they merit a special interest. Preliminary studies on phloem phenolics have
suggested dramatic changes in Scots pine, Pinus sylvestris L., in response to aggression (Lieutier et al. 1991a). This paper
presents the results from two complementary approaches recently developed in France concerning the possible role of
phenols in arresting bark beetle invasion and their use as biochemical markers of resistance. Detailed methods and other
findings are presented elsewhere (Lieutier et al. 1995).
METHODS
Experimental Devices
In our first experiment, six clones located in the INRA's nursery in Orlfians (France), each represented by one to three
10-year-old trees, were used to test if a relationship existed between reaction zone length and phenolic composition. Trees
were each inoculated with a malt agar sporulated culture of Ophiostoma brunneo-ciliatum Math.-K., a fungus previously
isolated from lps sexdentatus Boern., and thought to play a role in the establishment of this beetle in Scots pine (Lieutier et
al. 1988). Each tree received three inoculations. Three weeks later, the reaction zone around each inoculation point was
measured and sampled. Three samples of unwounded phloem were also taken from each tree.
Mattson, W.J., Niemel_i, P., and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle.
USDA For. Serv. Gen. Tech. Rep. NC-183, N.C. For. Exp. Sta., St. Paul, MN 55108.
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