VIEW ARTICLE

Ecology and Epidemiology

Northern Leaf Blight of Maize in New Zealand: Relationship of Drechslera turcia Airspora to Factors Influencing Sporulation, Conidium Development, and Chlamydospore Formation. C. M. Leach, Professor of Plant Pathology, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A.; 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 67:629-636. Accepted for publication 29 November 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-629.

Airborne conidia of D. turcica trapped above a diseased maize field were most abundant during days after warm nights with long continuous periods (10-12 hr) of high relative humidity (RH) (>90% approx.). Laboratory experiments confirmed that high atmospheric humidity is essential for sporulation. Conidiophores and conidia developed abundantly on young leaf lesions at RH’s above 92% and 94%, respectively. On newly formed conidiophores, slightly higher humidities were required for conidium formation than on old conidiophores. Free moisture on leaf lesions was not necessary for sporulation. Conidiophores were able to produce more than one batch of conidia as favorable conditions recurred. Temperature influenced the rate of development of conidia and also their morphology and septation. The lower limit of sporulation was approximately 9 C, the upper limit 30 C, and the optimum range was about 20 to 26 C. At optimum temperatures, conidium development (but not that of conidiophores) was inhibited by light. Exposure of conidiophores to at least 4 hr of continuous darkness (20 C) was required for conidium development. Under normal summer conditions near Pukekohe, New Zealand, D. turcica sporulated only on nights when atmospheric humidity was high for a continuous and extended period (approximately 10-12 hr) and then only if temperature was not limiting. Sporulation was lacking during the day because humidities generally were too low and because light inhibited conidium development. Under natural conditions, successive nights with relatively low temperatures (approximately 10 C) appeared to induce the formation of chlamydospores within conidia.