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Aphanomyces Blight of Amazon Sword Plants. W. H. Ridings, Plant Pathologist, Division of Plant Industry, Florida Department of Agriculture and Consumer Services, University of Florida, Gainesville 32601; F. W. Zettler, Associate Professor, Department of Plant Pathology, University of Florida, Gainesville 32601. Phytopathology 63:289-295. Accepted for publication 6 September 1972. DOI: 10.1094/Phyto-63-289.

An Aphanomyces sp. was frequently isolated from tissues of amazon sword plants (Echinodorus brevipedicellatus) affected by a previously unrecognized disease found at an aquatic plant nursery in South Florida. Suspensions of zoospores or mycelial fragments infected 28 of 45 inoculated plants of E. brevipedicellatus. Symptoms were the same as those observed under field conditions and on plants inoculated with water taken from containers with infected plants. The following alismataceous species did not become infected when inoculated: Echinodorus ‘Rangerii’, E. grisebachii, E. longistylis, E. martii, Sagittaria lorata, or S. sinensis. Likewise, inoculated specimens of Hydrilla verticillata, Myriophyllum spicatum, and Alternanthera philoxeroides remained healthy. The morphology of the oogonia, oospores, antheridia, and primary and secondary zoospores of this fungus was the same as that of published descriptions of A. euteiches and the two isolates of this species used for comparison. The amazon sword plant isolate infected seedlings of Pisum sativum, Beta vulgaris, Raphanus sativum, Vicia faba, and Vigna unguiculata (sinensis). Inoculated seedlings of Lycopersicon esculentum and Avena sativa did not become infected. The two A. euteiches isolates infected seedlings of P. sativum, but failed to infect B. vulgaris, R. sativum, A. sativa, L. esculentum, or E. brevipedicellatus.