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Pycnidial Release and Survival of Diplodia natalensis Spores. G. Eldon Brown, Plant Pathologist III, State of Florida Department of Citrus, Citrus Experiment Station, Lake Alfred 33850; Phytopathology 61:559-561. Accepted for publication 15 December 1970. DOI: 10.1094/Phyto-61-559.

Hyaline, single-celled spores of Diplodia natalensis were released from pycnidia growing on citrus deadwood when the pycnidia became wet or when they dried following wetting. Discharge occurred during or after rainfall for 1 or 2 summers, depending upon the development of the pycnidia at the completion of the first season. After discharge from the pycnidium, single-celled spores differentiated into darker-colored two-celled spores within 5 to 6 hr at 100% relative humidity. This process was interrupted when spores were placed at humidities below 100%, but continued upon return to 100% relative humidity. The two-celled spores were more tolerant to desiccation than the single-celled spores, and survived from 1 season to the next on the bark of naturally infected deadwood. As a result of the survival of these two-celled spores, infection of immature citrus fruit could occur even though pycnidia were not releasing spores.