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Inhibition of Conidial Germination and Germ Tube Growth of Cercospora canescens by Cowpea Leaf Diffusates. R. W. Schneider, Former Graduate Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801, Present address of senior author: Department of Plant Pathology, University of California, Davis 95616; J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 65:63-65. Accepted for publication 26 July 1974. DOI: 10.1094/Phyto-65-63.

Germination of conidia and germ tube growth of Cercospora spp. were observed in Nigeria to be inhibited on surfaces of young leaves, but not on older leaves, of cowpea (Vigna unguiculata ‘Prima’) which is susceptible to C. canescens. C. canescens conidia could not be distinguished from other Cercospora spp. on field-grown leaves since conidial morphology is not the sole taxonomic criterion. Germination of conidia and germ-tube growth of C. canescens were inhibited by diffusates from apical (but not basal) leaves of Prima, and by diffusates from apical and basal leaves of ‘Lalita’, resistant to C. canescens. Addition of nutrient broth to diffusates increased germination percentage and germ tube growth, but did not nullify inhibitory effects of the diffusates.

Additional keywords: Cereospora leaf spot, disease resistance.