Of the 13 downy mildew differential lines, five (HA 821, 265, 274,
DM 2, HA 799-2) were killed by P. halstedii systemic infection,
before WBR symptoms could be recorded. Of the remaining lines
six showed WBR infections between 7% (HAR 4) and 60% (QHP 1),
whereas two (PM 17, HA 803-1) remained free of symptoms.
Interestingly, all lines with high resistance to downy mildew (HAR
4, HAR 5, QHP 1 and HA 335) were infected by P. helianthicola with
QHP 1 showing the highest susceptibility of all differentials (Fig. 1).