Susnoschi, M., Division of Vegetable Crops, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

The yielding capacity of European potato varieties was tested in the spring and the autumn. The environmental characteristics for the spring crop (February-June) are increasing day length and temperature from planting to harvest, with the opposite for the autumn crops (August-December). In the spring crop, using imported seed tubers of about 5-6 months' chronological age, the stem density of different varieties varied between 120 000 and 240 000 per ha, and the weekly yield rates (total yield/growth period) were 2.6 and 4.7 t/ha. In the autumn crop, when local seed tubers of 3 months' chronological age were planted, the stem density was 2-3 times lower and the weekly yield rates were between 1.6 and 3.9 t/ha. Two groups of potato varieties were selected according to their yield performance as being suitable: a) for the spring crop cvs. Up-to-Date, Désirée and ZPC 71E207; and b) suitable for the autumn crop cvs. Désirée, Draga, Gulliver, Spunta, Ropta A3802, ZPC 71E277, and Cardinal. The variability in yield response of the S. tuberosum varieties to the high temperatures and short photoperiods of the semi-arid environment is discussed. © 1981 Kluwer Academic Publishers.