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Thirteen different isolates of virus X were made from the main New Zealand potato varieties. Twelve of these proved to be constant strains and the reactions of a number of plant species to them have been studied. All strains gave precipitin reactions with an antiserum prepared against one of them. Inoculation of Datura stramonium L. plants with an avirulent strain prevented their infection with the other strains. The relative severity of the strains on a number of test plants was similar. Nicotiana glutinosa L. was found to be satisfactory for the isolation and differentiation of most strains. Gomphrena globosa L. reacted with local lesions to all the strains. The symptom pictures of the strains have remained constant for 2 years except for one strain (XI), which showed a marked change in symptoms after 3 months in a deep-freeze unit. One isolate, AST1, contained both mild and severe components. Its passage through Cyphomandra betacea Sendt. resulted in the selection of a severe type. The same isolate contained a component which systemically invaded Chenopodium album L. No other strain produced systemic symptoms on this plant. |
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