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Ecology and Epidemiology

Northern Leaf Blight of Maize in New Zealand: Release and Dispersal of Conidia of Drechslera turcica. C. M. Leach, Professor of Plant Pathology, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; R. A. Fullerton(2), and K. Young(3). (2)(3)Plant Pathologist, and Biometeorologist, Plant Diseases Division, Department of Scientific and Industrial Research, Private Bag, Auckland, New Zealand. Phytopathology 67:380-387. Accepted for publication 29 September 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-380.

To determine the relations of spore release to changes in meteorological conditions, the incidence of conidia of the fungus Drechslera turcica was monitored continuously for 6.5 mo over a diseased maize crop at Pukekohe, New Zealand. Continuous measurements of wind, rain, relative humidity, duration of leaf wetness, and air temperature were made during the same period. Three types of spore release were discerned: (i) forcible discharge of conidia induced by rapidly falling relative humidity and exposure to solar radiation (diurnal discharge); (ii) wind release which occurred when wind velocities were greater than about 3 m/sec; and (iii) rain release. On many days, all three forms of release occurred and overlapped. Conidiophores also were trapped, particularly on dry, windy days not favorable for conidium development. The possibility that airborne conidiophores of D. turcica may act as infective propagules is discussed. Immature conidia (three or fewer septa) often were trapped and were capable of germination even when aseptate. Conidia containing chlamydospores were trapped during the late part of the growing season following periods of low night temperatures (10 C). Most airborne conidia were trapped during the day; few were trapped at night. Highest incidence of spores occurred during February-April (1974).

Additional keywords: Helminthosporium, Zea mays.