[Protocols]

1 - Let a Phytophthora brassicae mycelium grow in the dark, on a glass fiber filter, during 1 week, at 16°C, on V8 medium 20% agar*.
2 - Placed the filter with the P. brassicae mycelium on a soil medium**. Let it grow at the obscurity during 3 days, at 16°C (sporangia production).
3 - Placed the filter with the P. brassicae mycelium in a Petri dish with distilled water. Let it at 4°C during 4 hours to liberate the zoospores.
4 - Estimate the concentration of the P. brassicae zoospores suspension with a Nageotte cell (50 mm3). Heat briefly the cell to denature the flagella of the zoospores. Count the zoospores in 4 bands of the cell (x = zoospores number). (x / 5) gives the number of zoospores per ml.

Media :

* V8 medium 20% agar
200 ml of V8 (Campbell Juice), 3,5 g of CaCO3, 15 g of agar in 1 l of water.
Autoclave.

** Soil medium
Placed 800 ml of soil in a 1 l test tube, Complete with water until 1 l.
Let it 3 days at room temperature, Filtrate the mix with a nylon filter.
Autoclave the filtrate. Add 15 g of agar per l. of filtrate.