Basil Chlorosis: A Physiological Disorder in CO₂-Enriched Atmospheres. Kevin Wallick, Phytofarms of America, Inc., Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115. Thomas M. Zinnen, Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115. Plant Dis. 74:171-173. Accepted for publication 17 October 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0171.

Basil (Ocimum basilicum) grown commercially in a hydroponic facility under high-pressure sodium lights in a CO₂-enriched atmosphere developed a distinct interveinal chlorosis. Attempts to transmit the disease mechanically or by grafting to unaffected, greenhouse-grown basil and certain other plant species failed. Affected basil that was transferred from the hydroponic facility to a greenhouse and grown in potting mix produced new, chlorosis-free leaves. Under experimental conditions, basil became chlorotic in 1,000 ppm CO₂, but not when in ambient CO₂. This was true whether the basil was grown hydroponically or in pots, or under fluorescent or high-pressure sodium lights. Electron microscopy revealed no detectable pathogens, but large starch grains were observed in chloroplasts of chlorotic leaves. Elevated CO₂ concentrations apparently induced basil chlorosis.