Publication no. D-1999-0222-01R

Temperature, Leaf Wetness, and Isolate Effects on Infection of Minneola Tangelo Leaves by Alternaria sp. Y. Canihos, Assistant Professor, Department of Plant Protection, University of Cukurova, Adana, Turkey; and T. L. Peever, Visiting Assistant in Plant Pathology, and L. W. Timmer, Professor, University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Plant Dis. 83:429-433. Accepted for publication 18 January 1999. Copyright 1999 The American Phytopathological Society.

Alternaria brown spot causes necrotic lesions on immature leaves, twigs, and fruit of tangerines and their hybrids, reducing yield and fruit quality. The effect of temperature, leaf wetness, and isolate was evaluated in an in vitro system using immature detached leaves of Minneola tangelo. Infection was greatest at 27°C, decreased gradually as the temperature declined to 24, 20, and 17°C, and dropped sharply at 32°C. Levels of infection were low at 4 and 8 h of leaf wetness and continued to increase with longer wetting periods up to 36 h. A polynomial equation was developed that provided a good fit for the data (adjusted R(^2) = 0.93). Isolates differed in aggressiveness, but there was no significant difference among isolates in their response to temperature and leaf wetness duration.