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Postharvest Pathology and Mycotoxins

Relation of Postharvest Decay Fungi to the Slip-Skin Maceration Disorder of Dried French Prunes. P. L. Sholberg, Graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; J. M. Ogawa, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 73:708-713. Accepted for publication 1 December 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-708.

A postharvest disorder (“box rot”) of dried French prunes was studied. Symptoms of this condition are soft, sticky, macerated areas on the fruit and slippage of the skin under slight pressure. When fresh prune fruit were inoculated with Rhizopus arrhizus and R. stolonifer, more slip-skin maceration (SSM) disorder subsequently developed on dried prunes than when fruit were inoculated with other fungi such as Aspergillus japonicus, Penicillium expansum, Mucor circinelloides, Cladosporium herbarum, and Monilinia spp. Fresh fruit were commonly found to be naturally contaminated with Rhizopus spp. Fresh fruit held in bins at ambient field temperature for 24 hr or more after harvest subsequently developed SSM disorder after drying in proportion to the occurrence of prior Rhizopus infection. The following evidence, which implicates Rhizopus as the most common cause of SSM disorder, was provided. When fresh fruit were observed to be infected with Rhizopus spp. before drying, significant numbers of dried prunes exhibited SSM disorder; a high percentage of fresh prunes inoculated with Rhizopus spp. and incubated for 24 hr or more developed SSM disorder on drying; and tissue associated with SSM disorder on dried fruit obtained from commercial sources and from Rhizopus-inoculated fresh fruit that were dried contained a pectinolytic enzyme typical of that produced by Rhizopus spp. during decay of fresh fruit.

Additional keywords: pectinase, prune deterioration, Rhizopus rot.