Screening Shoot Cultures of Malus for Cedar-Apple Rust Infection by In Vitro Inoculation. H. Joung, Graduate Research Assistant, Department of Horticulture, University of Illinois, Urbana 61801. S. S. Korban, and R. M. Skirvin. Assistant Professor, and Associate Professor, Department of Horticulture, University of Illinois, Urbana 61801. Plant Dis. 71:1119-1122. Accepted for publication 16 June 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1119.

A simple and effective method for screening shoot cultures of Malus for resistance to the cedar-apple rust fungus (Gymnosporangium juniperi-virginianae) was developed. Shoot-tip cultures of Jonathan apple and Prairiefire crabapple cultivars were inoculated in vitro with a G. juniperi-virginianae basidiospore suspension and evaluated for rust symptoms. Jonathan, a susceptible cultivar, developed pycnial lesions of the rust within 10 days of inoculation, whereas Prairiefire, a resistant cultivar, showed no symptoms. No extraneous contamination was observed. In vitro inoculation of adventitious and axillary shoots derived from cotyledonary and embryo axis tissues, respectively, did not detect any somaclonal variation for resistance to the rust fungus.

Keyword(s): disease screening.