EVALUATION OF DIFFERENT POTATO CULTIVARS AT DIFFERENT IRRIGATION PERIODS AND DIFFERENT DROUGHT STAGES

Water deficit is an important stress factor in potato cultivation and leads to yield decrease. In order to evaluate 20 potato cultivars with respect to water deficit and select suitable varieties to arid and semi arid zones, an experiment was conducted in 2 years. In a 3 replicates RCBD design, 6, 12 and 18 days irrigation periods and three drought stages (from planting to emergence of seedlings, from emergence of seedling to tuber setting and from tuber setting till maturing) effects on emergence time, tuber setting and maturing date were measured. In the growth period, main and lateral stem number, diameter, plant height, tuber numbers, and tuber weights were measured. Combined Anova showed that, there were significant differences in irrigation treatments in tuber yield, tuber number, tuber weight, tuber bigger than 55 mm, and tuber number (35-55 mm). There were significant differences in tuber yield, tuber weight, tuber numbers (<35 mm) and tuber number (35-55 mm) among cultivars. Mean comparison of 2 years of irrigation periods showed that water stress led to decrease in tuber yield, tuber weight and tuber number (>55 mm). In comparison, control irrigation led to increase of 4.25 tons in tuber yield per ha with respect to mild condition and 12.18 tons in tuber yield per ha with respect to severe conditions respectively. Severe stress decreased tuber W by 174.7 g and tuber yield (>55 mm) number by 0.79. Water stress at planting time increased tuber yield, tuber number, tuber weight, tuber number (35-55 mm), tuber number (>55 mm) and decreased tuber number (<35 mm) more than tuber setting time. Tuber-setting stage was the most sensitive stage and led to the most decrease in yield. Vital, Mondial, Caesar, Draga, Cosmos, Cosima, Ilona and Granola showed the highest yield of 28.51, 27.83, 26.42, 26.01, 25.58, 24.81, 24.53 and 24.42 ton per ha, respectively. These cultivars also had the highest tuber number and tuber weight. Cosima, Vital, Serenade, Draga, Sinja and Idul produced high tuber number (35-55 mm). Correlation between tuber yield with tuber number, tuber W, tuber number (>55 mm) and leaf area was significantly positive and with PH and MSN was negative and non-significant. Modified stress tolerance index (MSTI) showed that Caesar, Vital, Ilona, Mondial and Draga had high tolerance to stresses in irrigation periods, and Mondial, Draga, Vital, Cosmos and Cosima had high tolerance to water stress. These cultivars showed high yield under stressed and non-stressed conditions. Cluster analysis showed four groups.