Abstract
In order to Study the effects of irrigation regimes on physiological traits, yield and water use efficiency of potato (Solanum tuberosum L.) in Mashhad weather condition, an experiment was conducted in 2009 at research field of the College of Agriculture, Ferdowsi University of Mashhad, using factorial experiment based on randomized complete blocks design with 3 replications. Experimental factors were 3 irrigation regimes including: I1: provided with 100% of water requirement of potato, I2: provided with 70% of water requirement of potato applied before tuber initiation and I3: provided with 70% of water requirement applied at all growth period of potato as first factors and 3 potato cultivars (Agria, Almera and Sinora) as second factors. The results indicated that about physiological traits when provided with 100% water requirement of potato the highest of relative water content, quantum efficiency of photosystem II, leaf area index and canopy height related to this irrigation regime. Even though with reduce in irrigation volume because of decreasing in LAI, the SPAD index in some cases was higher. Also in all irrigation regimes total tuber yield of Agria cultivar was better than to others. Considering to the calculation of water use efficiency with 30% decreasing in irrigation volume before tuber initiation, Agria had the highest WUE in provided with 70% water requirement. Finally, it seems that with decreasing in irrigation volume at Mashhad weather condition, Agria had the best growth and more acceptable yield compared to other genotypes.

Keywords: Potato, Irrigation regimes, Cultivar, Water Use Efficiency