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Ecology and Epidemiology

Establishment of Dicyma pulvinata in Cercosporidium personatum Leaf Spot of Peanuts: Effect of Spray Formulation, Inoculation Time, and Hours of Leaf Wetness. James K. Mitchell, Former graduate student, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, Texas A & M University, College Station 77843, Present address: Department of Plant Pathology, University of Arkansas, Fayetteville 72701; Ruth A. Taber(2), and Robert E. Pettit(3). (2)(3)Research scientist, and associate professor, respectively, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, Texas A & M University, College Station 77843. Phytopathology 76:1168-1171. Accepted for publication 29 April 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-1168.

Visible signs of colonization by Dicyma pulvinata on lesions of Cercosporidium personatum appeared within 58-65 hr (21-31.5 hr of leaf wetness) after inoculation in growth chamber experiments at 26 C. Spores of D. pulvinata suspended in distilled H₂O, 0.3% methylcellulose (CMC), 0.2% citrus pectin, or 0.25% ghatti gum colonized more lesions of C. personatum and at a faster rate when plants sprayed with D. pulvinata were subjected to an initial dry-leaf compared with an initial wetted-leaf incubation period. Spores of D. pulvinata suspended in CMC exhibited the least amount of variability in colonization rates between these two initial incubation periods. The efficacy of several different isolates of D. pulvinata for colonization of C. personatum also was investigated. Mutants were selected for growth under low relative humidity (RH80), high temperature (TR16), and resistance to benomyl (BR30). The isolate RH80 of D. pulvinata colonized lesions of C. personatum more rapidly than either the wild-type or BR30 isolates at 26 C.