Single spore infections with sunflower downy mildew.
A technique was developed to select vital zoospores of Plasmopara halstedii after zoosporogenesis for the infection of sunflower leaf disks. Successful infections were performed with samples containing several zoospores originating from a single sporangium as well as with samples containing only one single zoospore. Infections were indicated by spontaneous sporulation at the surface of inoculated sunflower leaf discs and were secured by transfer to whole seedlings. Using this method it was possible to generate unithallic infections and genetically homogenous strains of sunflower downy mildew.