VIEW ARTICLE

Physiology and Biochemistry

Free Sterol and Total Lipids in Stems of Susceptible and Resistant Tobacco Cultivars Colonized by Phytophthora parasitica var. nicotianae. L. D. Moore, Associate professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; D. M. Orcutt, Associate professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Phytopathology 72:1048-1051. Accepted for publication 12 January 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1048.

The susceptibility or resistance of plants of two flue-cured tobacco cultivars and one breeding line to Phytophthora parasitica var. nicotianae was not related to the total lipid or free sterol concentrations in the stems of control plants. Significant increases in lipid concentrations were recorded throughout the 12-day test period, as lesions developed in stems of highly susceptible cultivar Virginia Gold. Only at the second and 12th day did plants of moderately resistant cultivar North Carolina 88 and the highly resistant cultivar North Carolina 1071, respectively, contain significantly higher concentrations of total lipid. Early in disease development (day 2), colonized stems of Virginia Gold plants also had significantly higher concentrations of free sterols than stems of control plants. The free sterols cholesterol, campesterol, stigmasterol, and sitosterol were present in both control and colonized stems of each cultivar and line. Together, stigmasterol and sitosterol constituted 78–84, 63–78, and 64–77% of the free sterol concentrations in the stems of control plants of Virginia Gold. North Carolina 88, and North Carolina 1071, respectively. Although the free sterols and total lipids are not involved in either disease susceptibility or resistance, the increased concentrations of free sterols in the highly susceptible cultivar early in disease development may influence the rate of colonization by P. parasitica var nicotianae.