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Fusarium Boll Rot of Cotton: Pathogenicity and Histopathology. R. H. Sparnicht, Research Assistant, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30601; R. W. Roncadori, Associate Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30601. Phytopathology 62:1381-1386. Accepted for publication 12 June 1972. DOI: 10.1094/Phyto-62-1381.

Fusarium moniliforme, F. oxysporum, F. roseum, and F. solani decayed wounded green bolls in situ, but differences were noted in the rate of decay and type of tissue affected. Uninjured green bolls were rotted by F. oxysporum and F. roseum, which initially infected the bracts, and then invaded the capsule base through the receptacle. Disease development was affected significantly by boll age. Only artificially inoculated fruits 33 to 35 days of age or older decayed, even though younger bracts were infected. In the field, the pathogens became established in the bracts soon after bloom, but basal rot was observed only when bolls were 6 to 10 weeks old. Initial invasion of bract tissue occurred as intercellular hyphal growth in the mesophyll parenchyma and epidermis. Necrosis was observed only after intracellular penetration took place. In the latter stage of disease development, all tissues were colonized. A similar pattern of invasion occurred in the receptacle.