© 1998 Heron Publishing—Victoria, Canada
Hydraulic conductivity in roots of ponderosa pine infected with black-stain (Leptographium wageneri) or annosus (Heterobasidion annosum) root disease
Gladwin Joseph (1), Rick G. Kelsey (2) and Walter G. Thies (2)
1. Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA
/ 2. USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR 97331, USA / Received March 14, 1997
Summary
Roots from healthy and diseased mature ponderosa pine, Pinus ponderosa Laws., trees were excavated from a site near Burns, Oregon. The diseased trees were infected with black-stain root disease,
Leptographium wageneri Kendrick, or annosus root disease, Heterobasidion annosum (Fr.) Bref., or both. Axial hydraulic conductivity of the roots was measured under a positive head pressure of 5 kPa, and
the conducting area was stained with safranin dye to determine specific conductivity (ks). In diseased roots, only 8–12% of the cross-sectional xylem area conducted water. Resin-soaked xylem completely restricted
water transport and accounted for 13–16% of the loss in conducting area. In roots with black-stain root disease, 17% of the
loss in conducting area was associated with unstained xylem, possibly resulting from occlusions or embolisms. Based on the
entire cross-sectional area of infected roots, the ks of roots infected with black-stain root disease was 4.6% of that for healthy roots, whereas the ks of roots infected with annosus root disease was 2.6% of that for healthy roots. Although these low values were partly the
result of the presence of a large number of diseased roots (72%) with no conducting xylem, the ks of functional xylem of diseased roots was only 33% of that for healthy roots. The low ks values of functional xylem in diseased roots may be caused by fungus induced occlusions preceding cavitation and embolism
of tracheids. The ks of disease-free roots from diseased trees was only 70% of that for healthy roots from healthy trees. The disease-free roots
had the same mean tracheid diameter and tissue density as the healthy roots, suggesting that the lower ks in disease-free roots of diseased trees may also have been caused by partial xylary occlusions.
Keywords:
annosus root disease, black-stain root disease, Pinus ponderosa, root conductivity, specific conductivity, wood density.
