VIEW ARTICLE

Relativity of Limiting and Optimum Inoculum Loads, Wetting Durations, and Temperatures for Infection by Phytophthora infestans. J. Rotem, Division of Plant Pathology and Division of Statistics, The Volcani Institute of Agricultural Research, Bet Dagan, Israel; Y. Cohen(2), and J. Putter(3). (2)(3)Division of Plant Pathology and Division of Statistics, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Phytopathology 61:275-278. Accepted for publication 15 September 1970. DOI: 10.1094/Phyto-61-275.

The infection of potato leaves by Phytophthora infestans was investigated under controlled conditions, in a 6 × 5 × 4 factorial experiment with 120 combinations of temperature, inoculum concentration, and wetting duration. The minimum, maximum, and optimum levels of each factor were found to depend on the other two factors, in some cases primarily on one of them and in other cases on a balance of both. For each factor, both the limiting and the optimum range of levels were broad for favorable combinations of the other two factors, and narrow for unfavorable combinations. High spore load had an inhibiting effect when the wetting duration was 6 hours, and long wetting duration had an inhibiting effect when the temperature was 28 C. These findings imply that statements concerning the effect of any one factor on infectivity are relative rather than absolute, and are valid only under certain combinations of other factors which have to be explicitly specified.