Leaf Disk Immersion (LDI) Inoculation of Sunflower with Plasmopara halstedii for In Vitro Determination of Host-Pathogen Relationships. W. E. Sackston, Emeritus Professor, Department of Plant Science, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 1C0. Brigitte Vimard, Research Assistant, Department of Plant Science, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 1C0. Plant Dis. 72:227-229. Accepted for publication 9 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0227.

Sunflowers were successfully inoculated with downy mildew by immersing detached leaves (LI) or leaf disks (LDI) in suspensions of zoosporangia of Plasmopara halstedii for 3 hr at 15 C, then maintaining the leaves or leaf disks on water agar in petri dishes in an illuminated incubator at 15 C. Reactions in compatible and incompatible cultivar-race combinations were comparable to those of plants inoculated by the standard whole seedling immersion (WSI) method. LDI can be used to check the reaction of healthy "escapes" in compatible WSI inoculations, to check the race of P. halstedii on susceptible seedlings in incompatible combinations, and to determine the reaction of individual plants to several races of P. halstedii or to P. halstedii as well as to other pathogens.