A Detached-Leaf Technique for Detecting Resistance to Phytophthora parasitica var. nicotianae in Tobacco. E. C. Tedford, Research Specialist, Department of Agronomy, University of Kentucky, Lexington 40546. T. L. Miller, and M. T. Nielsen. Former Graduate Assistant, and Associate Professor, Department of Agronomy, University of Kentucky, Lexington 40546. Plant Dis. 74:313-316. Accepted for publication 23 October 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0313.

We developed a nondestructive technique for evaluating tobacco (Nicotiana tabacum) germ plasm for resistance to Phytophthora parasitica var. nicotianae. Leaves (7–9 cm long) from healthy tobacco plants were excised, surface-sterilized for 30 sec in a 0.05% NaOCl₃ solution, and inoculated with four mycelial plugs (1 cm in diameter) of 2-day-old P. p. var. nicotianae cultures grown on oatmeal agar. Inoculated leaves were placed in petri dishes containing one sterile filter paper and 10 ml of sterile distilled water. Petri dishes were sealed with Parafilm and incubated in a growth chamber at 27 C with constant fluorescent light (65 µE·m^–2·s^–1). Number of lesions per leaf and percentage of leaf area infected were recorded daily for 6 days after inoculation. Genotype rankings for lesion development and percentage of infected leaf area were similar to known rankings of the same genotypes for field resistance. The technique was not effective in detecting race-specific resistance derived from N. longiflora. The technique is quick, repeatable, and nondestructive, and it may be used in combination with detached-leaf screening techniques for other pathogens.