The potato crop ( Solanum tuberosum L.) is of great importance in the Uruguay economy, being the major vegetable in volume of trade. Uruguay imports some amount of potato seed annually. The National Institute of Agricultural Research (INIA) has been engaged for the last decades to obtain cultivars more adapted to country agroecological conditions, easier to multiply locally for replacing imported seed cultivars such as 'Chieftain'. In this sense, promising cultivars including 'INIA-Ipora' were developed. The objective of this work was to study the morpho-physiological and yield modifications of two potato cultivars ('Chieftain' and 'INIA-Ipora') under different irrigation managements. The experiment was carried out during 2006 and 2007 growing seasons under a rainout shelter, at the Experimental Station INIA Las Brujas, in Uruguay. These two varieties were studied under two irrigation managements: (i) irrigated treatment (2003/04 rainfall+irrigation according to daily crop ETc) and; (ii) deficit irrigated treatment (2003/04 rainfall+one irrigation of 25 mm when the accumulated maximum daily crop evapotranspiration reached 90 mm). The maximum daily crop evapotranspiration was estimated using the FAO Penman-Monteith equation. The experimental design was a completely randomized split plot. The leaf area index, the total plant photosynthesis and the crop yield better responded to the irrigation regime. The two potato cultivars showed differences in length of growing season, leaf area, number of mainstems, plant height and plant transpiration rates. The yield components were modified by the irrigation managements, and differences in commercial yield and total number of plant tubers were observed between the 'Chieftain' and 'INIA-Ipora' cultivars.
