Starch reserves in Piceaabies in relation to defence reaction against a bark beetle transmitted blue-stain fungus, Ceratocystispolonica

Abstract

Coniferous trees resist invasion of their phloem and xylem by microorganisms through an induced defence reaction; resin-filled reaction zones are formed around the infections to stop the intrusion. The efficacy of the reaction is supposedly dependent on an ample supply of carbohydrates. Two hypotheses were formulated: (i) phloem starch reserves are consumed by the defence reaction; (ii) trees low in phloem starch are vulnerable to infection. To test the hypotheses, stem sections of Piceaabies trees were mass inoculated with a pathogenic blue-stain fungus, Ceratoscystispolonica, associated with the spruce bark beetle Ipstypographus. Stem starch concentration was manipulated through girdling. Mass inoculation lead to a significant decrease in phloem starch concentration. Starch reserves of single trees were not correlated to their resistance to infection. Translocation capacity of the phloem is suggested critical for the defence reaction.