Histopathology of Pinus taeda needles infected by Ploioderma lethale

Abstract

The histopathology of the host/parasite relationship of Pinus taeda needles infected by the Ascomycete Ploioderma lethale and the morphology of the fructifications of the pathogen were investigated. Amphigenous elliptical teleo‐ and anamorph stromata developed only on dead portions of affected needles. Insertion of the teleo‐ and anamorph stromata in the host needle tissue was subepidermal, and the stromata were covered by a shiny to dull black clypeus. Teleomorph stromata frequently coalesced. Abnormal host tissue was primarily confined to tissues external to the endodermis in the symptomatic portion of affected needles, where a collapse of the mesophyll cells was exhibited. An obvious narrowing of affected needles was observed at the distinct juncture of dead and green tissue. Inter‐ and intracellular hyphae colonized the collapsed mesophyll cell regions, endodermal, transfusion, vascular tissues, and resin ducts. Intercellular hyphae and an interface were present in the living mesophyll cells of the green needle tissue subtending the dead terminal portion of affected needles.