Host resistance in defoliated pine: effects of single and mass inoculations using bark beetle-associated blue-stain fungi

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1 In 1996, 7000 ha of pine forests were defoliated by the pine looper Bupalus piniaria in south-western Sweden.

2 The susceptibility of trees of different defoliation classes (0, 30, 60, 90 and 100% defoliation) to beetle-vectored blue-stain fungi was tested in inoculation experiments. Forty and 120-year-old Scots pine trees were inoculated with ‘single’, i.e. a few inoculations of Leptographium wingfieldii and Ophiostoma minus, two blue-stain fungi associated with the pine shoot beetle Tomicus piniperda. The young trees were also ‘mass’ inoculated with L. wingfieldii at a density of 400 inoculation points per m2 over a 60 cm stem belt.

3 Host tree symptoms indicated that only trees with 90–100% defoliation were susceptible to the mass inoculation.

4 Single inoculations did not result in any consistent differences in fungal performance between trees of different defoliation classes, regardless of inoculated species or tree age class.

5 Leptographium wingfieldii produced larger reaction zones than O. minus, and both species produced larger lesions in old than in young trees.

6 As beetle-induced tree mortality in the study area occurred only in totally defoliated stands, mass inoculations seem to mimic beetle-attacks fairly well, and thus seem to be a useful tool for assessing host resistance.

7 As even severely defoliated pine trees were quite resistant, host defence reactions in Scots pine seem to be less dependent on carbon allocation than predicted by carbon-based defence hypotheses.

Keywords: Artificial inoculation; Bupalus piniaria; Leptographium wingfieldii; Ophiostoma minus; Pinus sylvestris; Tomicus piniperda; defoliation; host resistance; induced defense reaction

Document Type: Research Article


Affiliations: 1: Swedish University of Agricultural Sciences (SLU), Department of Entomology, PO Box 7044, S-75007 Uppsala, Sweden and 2: Norwegian Forest Research Institute (NISK), N-1432 Ås, Norway

Publication date: August 1, 2001

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