The penetration and growth of blue-stain fungi in the sapwood of lodgepole pine attacked by mountain pine beetle

Abstract

The growth of blue-stain fungi [Hyalorhinocladiella, Verticicladiella and Leptographium] was investigated in naturally blue-stained P. contorta var. latifolia Engelm. sapwood. Events occurring at the leading edge of hyphal penetration were studied. Fungi are initially confined to the sapwood rays. Hyphae rapidly penetrate the primary cell walls of ray parenchyma cells and proliferate within. Hyphae also grow freely in the region of the middle lamella of the rays. Host cell walls are breeched mechanically by a penetration peg originating from an appressoriumlike structure. Eventually, hyphae enter tracheids by penetrating the primary cell walls of pinoid, half-bordered pit pairs. Within the tracheid, fungal hyphae grow in a longitudinal fashion, branching infrequently. Hyphae may pass from tracheid to tracheid via bordered pit pairs. Ensuing water stress and eventual tree death is discussed in light of histological evidence presented.