THE INCREASE IN CONCENTRATION OF TWO STRAINS OF POTATO VIRUS X IN FLOATING LEAF DISCS

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Abstract
Increases in concentration of two antigenically similar strains (ringspot and yellow) of potato virus X (PVX) in Nicotiana tabacum L. vars. Samsun and Havana 38 and in Nicotiana rustica L. were determined serologically and by local lesion assay. In discs of inoculated leaf tissue floating on Hoagland's solution the rate of increase was greatest at 16° and 20 °C. In Samsun the optimum temperature for the increase in virus concentration was lower for the yellow strain than the ringspot strain. A close correlation between the assay procedures indicated that, as the temperature increased above the optimum for virus increase, either virus synthesis was being inhibited or virus was being denatured. No differences were found where 8- and 16-hour photoperiods were compared to determine their effect on virus increase at 20 °C. Virus concentrations in Samsun and Havana 38 were similar when determined under similar conditions. Concentrations in N. rustica were appreciably higher. In both Nicotiana species the concentration of the yellow strain at any time after inoculation was lower than that of the ringspot strain.