Figure 4.

Potato infection by Spongospora subterranea. The potato pathogen Spongospora subterranea infects host tubers, roots and stolons, resulting in the development of powdery scab lesions (A) and galls (B). These usually appear in potato crops 2–3 months after planting, and mature to release sporosori (conglomerations of resting spores). A sporosorus contains 500–1000 resting spores, each containing a primary zoospore (D; bar, 10 µm). Secondary zoospores formed in zoosporangia (C; bar, 20 µm) emerge through root cell walls, disrupting host nutrient and water uptake.