VIEW ARTICLE

Pectic Enzymes Associated with Black Root Rot of Tobacco. Laraine M. Unbehaun, Former NSF Fellow, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute, Blacksburg 24061, The senior author is now Assistant Professor, Department of Biology, Wisconsin State University, La Crosse 54601; Laurence D. Moore, Assistant Professor of Plant Pathology, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute, Blacksburg 24061. Phytopathology 60:304-308. Accepted for publication 12 September 1969. DOI: 10.1094/Phyto-60-304.

Extracts of healthy and Thielaviopsis basicola-infected Vesta 5 (susceptible) and Virginia Gold (resistant) tobacco root tissue were tested for pectic enzyme activity. Pectin methylesterase activity was high in extracts from diseased and healthy root tissues of both varieties, healthy tissue possessing about two-thirds as much pectin methylesterase activity as diseased tissue. Healthy root tissue of both varieties contained low levels of endopolygalacturonase and endopolygalacturonate-trans-eliminase activity, and exhibited no macerating activity. Diseased root tissue of both varieties possessed a high level of endopolygalacturonate-trans-eliminase activity and moderate endopolygalacturonase activity. Macerating activity of extracts of diseased tissue was high in the pH range 8-9.5, corresponding to the optimum pH range for endopolygalacturonate-trans-eliminase activity, and moderate in the pH range 4-5, corresponding to the optimum pH range for endopolygalacturonase activity. The similar activity pattern for enzymes from diseased tissue of Vesta 5 and Virginia Gold indicated that the pectic enzyme activity present in both varieties was similar. The principal difference between the susceptible and resistant varieties was that pectic enzyme activity increased more rapidly and to a higher level after inoculation in Vesta 5 (susceptible) than in Virginia Gold (resistant). Since increases in endopolygalacturonate-trans-eliminase activity coincided closely with symptom development, endopolygalacturonate-trans-eliminase appeared to be largely responsible for degradation of diseased root tissue during colonization.