Methodolagy of drought resistance evaluation for potato germplas and path analyses of yield and its compenents.

Water deficit is a common stress types in potato cultivation and charge as yield decrease factor. This experiment was conducted on 20 potato cultivars in three limited irrigation regimes (from planting to emergence, from emergence to tuberization, and tuberization) and three irrigation periods (6, 12 and 18 days) by use of a three replicated RCBD design for two years. Combined ANOVA were showed that there were significant differences for irrigation treatments between tuber yield, number and weight of tuber per plant, tuber number between 35-55 mm (TN 35-55mm) and bigger than 55 mm (TN55mm). So differences between cultivars were significant for tuber yield (TY), number and weight of tuber per plant (TN and TW), tubers number less than 28mm (TN28mm) and between 35-55 mm. Means comparison of under study cultivars in different irrigation regimes for two years showed that water stress was decreased TY, TW and TN55mm. Non-stressed condition (six days) increased tuber yield relative to medium stress (12 days) and sever stress (18 days) with rate of 4.25 and 12.18 ton/ha, respectively. During of two years experiment of irrigation limitation at planting to emergence stage relative to tuberization stage increased TY, TN, TW, TN 35-55mm, TN55mm and decreased TN28mm. Vital, Mondial, Caesar, Draga, Cosmos, Cosima, ILona and Granola were showed the highest yield. Also, these cultivars had more TN and TW. Correlation between TY with TN, TW, TN 55mm and leaf area was significantly positiveand with plant height (PH) and main stem number (MSN) was not negatively significant. Modified stress tolerance index (MSTI) showed that Caesar, Vital, Ilona, Mondial and Draga had high tolerance to irrigation periods and Mondial, Draga, Vital, Cosmos and Cosima had high tolerance to water stress by attention to irrigation limitation. These cultivars showed higher yield than others in stressed and non-stressed conditions. Path Analyses showed that TN, TW, PH and leaf area had important positive effect, and MSN, LN, TN 28mm and TN 35-55mm had the most important negative effect on tuber yield.