Studies on relation between host and pathogen of sunflower downy mildew (Plasmopara helianthi Novot.).
Of 72 sunflower cultivars and lines tested under controlled conditions, 17 were resistant to P. helianthi [P. halstedii]. On inoculation, mycelia and oospores were detected in roots and hypocotyls of all the resistant cultivars, but no fungal structures were found in sections of the epicotyl. No relationship was found between phytoalexins of resistant and susceptible cultivars and disease resistance.