Increased Chlamydospore Production byPhytophthora cinnamomiUsing Sterols and Near-Ultraviolet Light

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Abstract
A regimen was developed using near-UV light, temperatures of 23-28.degree. C, and a natural medium (V8 agar) supplemented with .beta.-sitosterol for consistently producing high yields of chlamydospores of P. cinnamomi. Addition of .beta.-sitosterol to V8 agar at 10-40 .mu.g/ml stimulated chlamydospore production in cultures incubated in the light but not in those incubated in the dark. In the dark, growth (dry weight) was stimulated by sterol at 20 and 40 .mu.g/ml; in the light, however, no stimulation was detected with sterol up to 200 .mu.g/ml. Chlamydospores produced on V8 agar plus sterol were more abundant in cultures illuminated with 100, 200 or 400 .mu.W cm-2 light in the 310-420 nm (near-UV) region than in the 470-610 or 550-725 nm region at the same intensities or in the dark. Chlamydospore production comparable to that in 310-420 nm light was obtained with Blacklight Blue fluorescent lamps, which emit predominantly near-UV light. Optimum intensity of Blacklight Blue light for sporulation was 100-200 .mu.W cm-2.