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Etiology

Moderate Dosages of Ozone Enhance Infection of Onion Leaves by Botrytis cinerea but not by B. squamosa. D. L. Rist, Graduate research assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853; J. W. Lorbeer, professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853. Phytopathology 74:761-767. Accepted for publication 2 January 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-761.

Exposure of onion plants to moderate chronic dosages of ozone under controlled conditions resulted in predisposition of the older leaves to enhanced infection by Botrytis cinerea. More lesions per square centimeter of leaf surface were induced by B. cinerea on the two oldest nonsenescing leaves of plants of ozone-sensitive onion cultivars Autumn Spice and Fiesta inoculated after 4-hr exposure to 0.16 ppm (314 μg/m³) of ozone (a dosage rarely, if ever, encountered in New York) than were induced on the corresponding leaves of nonexposed plants. This effect occurred in both the presence and absence of macroscopically visible, ozone-induced leaf injury. Similar results were obtained following inoculation with B. cinerea of plants exposed or not exposed to the relatively high chronic dosage of 0.12 ppm (235 μg/m³) of ozone for 5 hr per day for 4 days. More lesions per square centimeter of leaf surface were induced by B. squamosa on the two oldest nonsenescing leaves of exposed than on nonexposed plants (cultivar Autumn Spice) but only after exposure to the relatively high acute dosage of 0.25 ppm (490 μg/m³) of ozone for 4 hr (a dosage rarely, if ever, encountered in New York). Exposure of onion plants (cultivar Autumn Spice) infected with B. cinerea or B. squamosa to the relatively high chronic dosage of 0.14 ppm (274 μg/m³) ozone for 5 hr per day for 5 days had no detectable effect on expansion of preestablished lesions induced by these pathogens.