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Pathogenicity of Pythium myriotylum and Other Species of Pythium to Caladium Derived From Shoot-Tip Culture. W. H. Ridings, Plant Pathologist, Bureau of Plant Pathology, Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Gainesville 32602; R. D. Hartman, Former Research Assistant, Department of Plant Pathology, University of Florida, Gainesville 32611, Present address of junior author: Plant Pathologist, Pan-American Plant Co., P.O. Box 428, West Chicago, Illinois 60185. Phytopathology 66:704-709. Accepted for publication 25 November 1975. DOI: 10.1094/Phyto-66-704.

Isolates of Pythium obtained from diseased caladium roots were identified as P. irregulare, P. myriotylum, and P. splendens. Pathogenicity studies with these species of Pythium at 24 C and 32 C showed P. myriotylum and P. splendens to be infective. The shoot, corm, root, and total plant weights after 40 days showed that only P. myriotylum reduced plant growth significantly (P < 0.05) at 32 C. No significant differences (P < 0.05) were noted for any of the species at 24 C. Greenhouse inoculations with P. myriotylum significantly slowed (P < 0.05) the germination of corm pieces and resulted in significant losses (P < 0.01) in total plant growth after 28 weeks.

Additional keywords: Caladium hortulanum, root infection.