VIEW ARTICLE

Fusarium Wilt of Susceptible and Resistant Tomato Isolines: Histochemistry of Vascular Browning. M. E. Mace, Plant Pathologist, Disease Resistance Investigations, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; J. A. Veech(2), and C. H. Beckman(3). (2)Plant Physiologist, Disease Resistance Investigations, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; (3)Professor, Department of Plant Pathology-Entomology, University of Rhode Island, Kingston 02881. Phytopathology 62:651-654. Accepted for publication 19 January 1972. DOI: 10.1094/Phyto-62-651.

The substrate for initial vascular browning in wilt-resistant or susceptible tomato isolines infected with Fusarium oxysporum f. sp. lycopersici, race 1 or 2, is localized in scattered xylem parenchyma cells. Brown products diffuse from these localized sites into surrounding xylem tissues. Phenols were detected histochemically in the xylem parenchyma cells during initial or early stages of browning. The histochemical data indicate that the major type of phenol localized at the sites of vascular browning is an o-dihydric phenol with an unsubstituted position para to one of the hydroxyl groups. Phenols were not detected histochemically in the healthy, nonbrowned xylem parenchyma. These observations suggest that the phenols may occur in the healthy stem xylem in conjugated forms from which free, oxidizable phenols are released after infection. Where localized vascular browning occurred, no differences in the histochemical reactions were noted between the two tomato cultivars inoculated with race 1 or 2 of F. oxysporum f. sp. lycopersici.