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The Nature of Virus Inhibition by a Polysaccharide from Phytophthora infestans. R. P. Singh, Research Station, Canada Department of Agriculture, Fredericton, New Brunswick; F. A. Wood(2), and W. A. Hodgson(3). (2)(3)Research Station, Canada Department of Agriculture, Fredericton, New Brunswick. Phytopathology 60:1566-1569. Accepted for publication 1 June 1970. DOI: 10.1094/Phyto-60-1566.

A polysaccharide isolated from Phytophthora infestans completely inhibited local lesion development by potato virus X on Nicotiana tabacum ‘Samsun’ without inhibiting virus multiplication. The inhibitory effect was instantaneous. Dilution or centrifugation of the virus :polysaccharide mixture restored virus infectivity. Maximum inhibition resulted when virus and polysaccharide were applied as a mixture or when the polysaccharide preceded the virus. The polysaccharide was confined to the epidermal layer of tobacco, and was not translocated from the site of application. It is suggested that polysaccharide inhibits virus entry by modifying infectible sites on the leaf surface, but the mechanism involved in masking of lesions is not understood.