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Factors Affecting Bioassay of Potato Virus S in Chenopodium quinoa. C. Hiruki, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3; Phytopathology 65:1288-1292. Accepted for publication 10 June 1975. DOI: 10.1094/Phyto-65-1288.

Various factors affecting production of potato virus S (PVS) lesions on leaves of Chenopodium quinoa were investigated to determine optimal conditions for the local lesion test. All bioassays were carried out using intact plants under controlled environment conditions. PVS extracts were obtained from infected leaves of potato (Solanum tuberosum) at a ratio of 1:10 in 1% K2HPO4 at pH 8.0. The maximum local lesion number was obtained at 27 C with a light period of 16 hours. Light intensities suitable for the assay were 5,380 to 10,760 lx. Dark treatment of C. quinoa for 24 hours before inoculation significantly increased the susceptibility of the assay plants. Highly susceptible C. quinoa plants, a Canadian selection, with four to six leaves of uniform size were obtainable for assay 40 to 60 days after seeding, and consistently produced numerous local lesions 8-10 days after inoculation at 25 C. In contrast, a European selection was less susceptible than was the Canadian selection and produced a very few lesions in 10-12 days under the same conditions.

Additional keywords: local lesion host, potato virus S infectivity test.