VIEW ARTICLE

Physiology and Biochemistry

Interaction of Light and Sterol on Sporangium and Chlamydospore Production by Phytophthora lateralis. L. Englander, Assistant professor, Department of Plant Pathology-Entomology, University of Rhode Island, Kingston 02881; L. F. Roth, professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 70:650-654. Accepted for publication 19 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-650.

Chlamydospore production by Phytophthora lateralis was most abundant in V8 broth with 20 μg/ml β-sitosterol, and maximum sporangium production occurred with 10 μg/ml. Growth (dry weight) was not enhanced by sterol concentrations ranging from 1 to 200 μg/ml. Cultures grown on V8 sterol agar or broth, and illuminated (680 μW cm^–2, combined Blacklight Blue and Cool White fluorescent lamps) either continuously or 12 hr daily, produced at least four times as many sporangia as were produced by cultures in the dark on sterol media, or in the light or dark on media not amended with sterol. Chlamydospores were produced most abundantly in the dark on V8 sterol agar or broth, with production greatly reduced by continuous or 12 hr of light daily. Chlamydospore production was suppressed by all light intensities tested (85, 170, 340, 680 μW cm^–2) compared with production in the dark. Few chlamydospores formed in cultures on media without sterol, whether incubated in the light or dark. Growth (dry weight or colony size) was not affected by illumination. None of numerous regimes of diurnal temperature cycles enhanced sporulation more than constant temperatures. Optimal sporangium production requires incubation on media with sterol at 14–16 C in the light; optimal chlamydospore production requires incubation at 24–25 C in the dark on media with sterol.