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Flooding-associated soft rot of sweet potato storage roots caused by Clostridium.
W. L. DA SILVA (1), C. Clark (1). (1) Louisiana State University Agricultural Center, Baton Rouge, LA, U.S.A.

Sweet potato storage roots are commonly destroyed by a rapid soft rot that develops when fields are flooded. The purpose of this work was to identify the pathogens responsible for development of that soft rot. Samples were collected from storage roots with soft rot from intentionally flooded fields and decayed tissue was streaked on plates of nutrient dextrose agar plus 0.05% cysteine. Symptomless sweet potato storage roots were stab inoculated with bacterial isolates, then wrapped with moist paper towels, kept in plastic bags, and incubated at 25°C for 4 days. Ten Gram positive bacteria were re-isolated from rotting storage roots that were able to grow in anaerobic but not in aerobic atmospheres. Endospores were observed in all isolates by differential staining. Six of the isolates had pectinase activity as indicated by pit production in double-layer pectate medium and caused soft rot symptoms in storage roots. Genomic DNA was extracted from representative colonies and the 16s ribosomal RNA region was amplified using primers FD1 and RD1 and the PCR products were sequenced. BLASTn analysis of the 1425 bp sequence resulted in 98% homology with <i>Clostridium puniceum</i> strain BL 70/20 from rotting Irish potatoes (GenBank Accession No. NR_026105.1). Understanding the role of pectolytic clostridia in flood-induced soft rotting will be vital in managing sweet potato crop losses following hurricanes and other flooding events.<p><p>Keywords: Bacteria-Phytoplasma-Spiroplasma-Fastidious Prokaryote, Root-Tuber Crops, Sweet Potato

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