View or print this publication - Northern Research Station - USDA ...

GENETIC AND PHENOTYPIC VARIATION IN THE INDUCED REACTION OF
SCOTS PINE TO LEPTOGRAPHIUM WINGFIELDII:
REACTION ZONE LENGTH AND FUNGAL GROWTH
F. LIEUTIER 1,B. LANGSTROM z, H. SOLHEIM 3
C. HELLQVIST 2, and A. YART l
_Station de Zoologie Foresti_re, Institut National de la Recherche Agronomique, Ardon, 45 160 Olivet, France
2Division of Forest Entomology, Swedish University of Agricultural Sciences, S-77073 Garpenberg, Sweden
3Department of Forest Ecology, Norwegian Forest Research Institute, As-NLH, N 1432, Norway.
INTRODUCTION
The induced defensive reaction of phloem generally plays a decisive role in the resistance of conifers to attack by
bark beetles and their associated fungi. It is thought to be induced by fungi (Reid et al. 1967, Berryman 1972, Raffa and
Berryman 1983, Christiansen and Horntvedt 1983, Matson and Hain 1985, Christiansen et al. 1987, Lfingstr6m et al. 1992),
or by the boring activity of the beetle (Lieutier et al. 1988, Lieutier 1993). In most cases, by stimulating that energy demanding
response, the fungi can lower the threshold of attack density above which the tree is overwhelmed and beetle attacks are
successful. In all situations, the individual reaction is the basic mechanism of tree resistance.
The between-tree variability in the threshold of attack density (Waring and Pitman 1980, Mulock and Christiansen
1986), as well as the between-tree variability in the induced reaction itself (Shrimpton and Reid 1973, Peterman 1977,
Lieutier and Ferrell 1989, Lieutier et al. 1993), has been linked to tree vigor. However, the genetic contribution to this
variability has never been studied.
In Scots pine, Pinus sylvestris L., an induced reaction is essential to resist attacks by lps sexdentatus Boern. and
Tomicus piniperda L., and their associated fungi (Lieutier et al. 1988, 1989a; Solheim and L_ngstr6m, 1991; L_ngstr_m et al.
1992). The blue-staln fungus, Leptographium wing_i'eldii Morelet, associated with T. piniperda, does not seem to play a role
in the development of the induced reaction and in the success of attacks (Lieutier et al. 1988, 1989b). However, artificial
inoculation of its sporulated cultures into Scots pine always incites strong defensive reactions (Lieutier et al. 1989a, Solheim
and L_ngstr6m 1991) and the tree's response depends on the number of spores present in the inoculum (Lieutier et al. 1989b).
Additionally, it may play a role in tree mortality, since weakened Scots pine can be killed by a high density of artificial
inoculations (Solheim et al. 1993).
The present study is part of a cooperative project with the following objectives: (1) to study the variation in the
induced reactions (reaction zone formation, sapwood occlusion) between Scots pine provenances in two different climatic
regions, (2) to study the performance of a French and a Swedish strain of L. wingfieldii in these provenances under different
climatic conditions, and (3) to study the defensive chemistry involved in the induced reactions, particularly the roles of resin
acids and phenolics, and to search for chemical markers for resistance among these groups of chemicals. This study addresses
the first two issues.
Mattson, W.J., Niemelfi, P., and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle.
USDA For. Serv. Gen. Tech. Rep. NC-I83, N.C. For. Exp. Sta., St. Paul, MN 55108.
166