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Ecology and Epidemiology

Pathogenicity, Fungicide Resistance, and Ethylene Production of Penicillium spp. Isolated from Tulip Bulbs. T. A. Prince, Former graduate research assistant, Department of Horticulture, Michigan State University, Present address: Department of Horticulture, The Ohio State University, 2001 Fyffe Court, Columbus 43210; C. T. Stephens(2), and R. C. Herner(3). (2)Associate professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; (3)Professor, Department of Horticulture, Michigan State University, East Lansing 48824. Phytopathology 78:682-686. Accepted for publication 2 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-682.

Three isolates of Penicillium corymbiferum and one isolate of P. rugulosum obtained from tulip bulbs (Tulipa gesneriana L.) shipped from the Netherlands were shown to be pathogenic on excised basal plates of precooled tulip bulbs. One isolate of P. corymbiferum was benomyl resistant when cultured on benomyl amended potato-dextrose agar (PDA). Etaconazole and prochioraz fungicides controlled growth of this isolate in vitro. The benomyl-resistant isolate produced 1.5 μl/cm²/hr of ethylene when grown on PDA. The other isolates did not produce ethylene on this medium. Inoculation of benomyl pretreated, excised basal plates with a mixed spore suspension of the same two isolates yielded a predominance of benomyl-resistant colonies after 1 wk. Etaconazole pretreatment controlled infection of excised basal plates by both isolates. Ethylene levels in sealed modified atmosphere film packages of bulbs remained similar through 2 wk after bulb basal plates were inoculated with an ethylene producing (benomyl-resistant) or a non-ethylene producing (benomyl-susceptible) isolate of P. corymbiferum. However, after 3 wk of storage there were higher ethylene levels in the packages containing the ethylene producing isolate even though the disease levels were similar.