OBJECTIVETo study the pathogen of opium poppy downy mildew and its biological characteristic for further research on the disease.

METHODDevelopment of the disease was observed systematically in the field. Germination rate of sporangium in different temperature, pH and nutrition was examined with suspending-drop method. Slide-germination method was used to observe its germination in different humidity maintained by different concentration of H2SO4.

RESULT AND CONCLUSIONThe disease manifests itself in two forms: severely infected plants (systematic infection) and leaf spots (nonsystematic infection). Sporangia of the pathogen are oval or globular, thin walled, smooth, hyaline, with 7.74-16.34 microns diameter in base 1 and 8.34-15.05 microns in base 2.0 ospores are light yellow with 33.87-70.54 microns x 19.34-62.64 microns in base 1 and 36.85-49.68 microns x 42.08-55.76 microns in base 2. Conidiophores are stout, erect, whose branching times and length are different between those in base 1 and those in base 2. Sporangia sprot directly in two hours. Film of water is necessary for sporangium to sprot. The optimum temperature range of sporangium sprot is 12-21 degrees C, the best being 16 degrees C, the pH range is 4.53-9.18 the best optimum at pH 7.38, and the extract of leaf of 1:5 is good for its germination.