Plasmopara halstedii (Farl.) Berl. et de Toni in sunflower seeds and the role of infected seeds in producing plants with systemic symptoms.
Light microscopic observations revealed fungal structures in 28% of mature seeds collected from sunflower plants systemically infected by P. halstedii. Mycelium was found only in the testa and in the inner layer of the pericarp; it was absent from the embryo. Emergence of seeds from infected plants was 6-8% lower than that of seeds from healthy plants, but seeds from infected plants rarely gave rise to plants exhibiting systemic symptoms of P. halstedii. Nevertheless, it is concluded that infected seeds play a major role in disease transmission by introducing primary inoculum into hitherto uninfected areas.