VIEW ARTICLE

Ecology and Epidemiology

Effect of Reducing Oxidant Injury and Early Blight on Fresh Weight and Tuber Density of Potato. J. D. Holley, Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1; G. Hofstra(2), and R. Hall(3). (2)(3)Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1. Phytopathology 75:529-532. Accepted for publication 28 November 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-529.

Ethylene diurea (EDU) significantly protected potato foliage from visible injury due to ozone (O₃) in laboratory and field experiments, but did not induce significant increases in fresh weight or specific gravity of tubers at harvest. Ambient O₃ concentrations were low, and the severity of oxidant injury was too small to have an impact on yield. Fentin hydroxide (Du-Ter) did not diminish O₃ injury on potato leaves in controlled fumigations, but did significantly reduce adaxial bronzing in the field. The potato early blight pathogen, Alternaria solani, was frequently isolated from leaf tissue with adaxial bronzing. Significant increases in the fresh weight of tubers of the cultivar Norchip, and the overall specific gravity of tubers from all cultivars, showed a greater-than-additive response in the treatment combination of Du-Ter and EDU when compared to increases in either single spray treatment. The effects of Du-Ter, either singly or in combination with EDU, indicated that adaxial O₃ lesions became colonized by A. solani under natural field conditions. Regression equations relating changes in yield to percentage changes in apparent infection rate or rate of defoliation from early blight and O₃ showed that cultivar tolerance is a major factor to consider when assessing the importance of controlling symptoms of oxidant injury or early blight on potato.