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Effect of Temperature and Boll Injuries on Development of Diplodia Boll Rot of Cotton. S. M. McCarter, Assistant Professor, Department of Plant Pathology and Plant Genetics, University of Georgia, Athens 30601; Phytopathology 62:1223-1225. Accepted for publication 8 May 1972. DOI: 10.1094/Phyto-62-1223.

Diplodia gossypina grew best on potato-dextrose agar and rotted cotton bolls most rapidly at 30 C. At 30 C, bolls were often completely decayed in 4 days when mycelial inoculum was placed over a deep wound made through the pericarp with a dissecting needle, whereas 9 to 11 days were usually required for complete rot of noninjured bolls. Decay of the entire boll occurred in 5 to 7 days when inoculum was placed over a shallow wound (surface scratched) or between artificially cracked sutures. Sixteen isolates of D. gossypina from cotton bolls differed more in aggressiveness on noninjured bolls than on bolls punctured with a dissecting needle. These results indicate that both high temperatures and boll injuries are important factors in the rapid development of Diplodia boll rot.

Additional keywords: Gossypium hirsutum, ingress, isolate virulence.