Physiological response of Pinus taeda L. trees to stem inoculation with Leptographium terebrantis

Abstract

Young Pinus taeda trees may tolerate Leptographium terebrantis infection when stand conditions support new sapwood growth devoid of pathogen-induced occlusion. Leptographium terebrantis S. J. Barras and T. J. Perry is an opportunistic root pathogen that compromises the xylem function of infected trees and is commonly associated with Pinus taeda L. stands that experience an unexplained loss of vigor in the southeastern U.S. To understand the relationship between L. terebrantis inoculation density, sapwood occlusion, and sapwood function characterized by hydraulic conductivity and moisture content, an artificial inoculation study was conducted in young P. taeda trees in a naturally regenerated stand over a 24-week period in south central Alabama. Four levels of increasing stem inoculation were used as a surrogate for comparable levels of woody root inoculation followed by an evaluation of pathogen-induced occlusion, sapwood function, and fascicle physiology. Occlusion of old sapwood intensified as L. terebrantis inoculum density increased, but occlusion was absent in current-year sapwood. Occlusion reduced sapwood hydraulic conductivity and moisture content but did not interfere with stomatal conductance. The vertical spread of L. terebrantis was correlated with losses of sapwood hydraulic conductivity and moisture content due to occlusion. Results demonstrate that the sapwood function of P. taeda is tolerant of the pathogen vascular occlusion when stand conditions sustain adequate carbon fixation for occlusion-free stemwood growth.