New Race of Plasmopara halstedii Virulent on Resistant Sunflowers in South Dakota. M. L. Carson, Assistant Professor, Plant Science Department, South Dakota State University, Brookings 57007. Plant Dis. 65:842-843. Accepted for publication 28 July 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-842.

A new race of Plasmopara halstedii capable of overcoming the PI₂ monogenic resistance in sunflower (Helianthus annuus) has been found in a hybrid demonstration plot near Brandt, SD. None of the known sunflower genes resistant to P. halstedii are effective against this race.

Keyword(s): downy mildew, pathogen variability.