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The main objective of this study was to assess responses of mid-early (Spunta) and mid-late (Bellini) potato cultivars to different temperature regimes during subsequent stages of potato growth. The impact of high temperature (25/22°C day/night), low temperature (18/16°C day/night) and intermediate temperature (20/18°C day/night) was evaluated for different growth stages. Data were obtained for photosynthesis, carbohydrates in leaves, stems and tubers as well as production parameters. Enzyme activities were determined for sucrose-phosphate synthase in leaves, acid invertase in stems and acid and neutral invertases in tubers. Gene expression levels of relevant sugar metabolizing enzymes was quanti ed.A detailed correlation analysis revealed a strong impact of the expression level of sugar metabolizing enzymes in leaves on the nal number of tubers per plant.Whereas total tuber yield increases with temperature, the number of tubers per plant was highest under low temperature conditions. Our data suggest an important role of the temperature on the length of the different growth stages. Key MessageRe-evaluation of earlier reports regarding temperature effects on potato tuber yield using two different, mid-early and mid-late ripening potato varieties led to unexpected results for most of the determined crop parameters such as carbon partitioning, carbon metabolism, tuber yield and time of tuber maturation.This study was undertaken to determine the physiological, biochemical, enzymatic and genetic behavior of mid-early and mid-late maturing potato cultivars subjected to different temperatures. Experiments were carried out to evaluate relevant parameters concerning photosynthesis (Fo, Fm and Fv/Fm), soluble sugar content and starch accumulation as well as their distribution in source and sink organs, the expression levels and activities of sugar metabolizing enzymes including AGPase, invertases, SPS and sucrose synthase in leaves, stems or tubers, as well as production parameters, in order to determine the optimal temperature for the tuberization according to length of the development cycle of the potato cultivar.

In this work, we studied agro-morphological parameters that could be used to define variaton among early, mid-early, mid-late and late potato cultivars, cropped in the main season by quantitaive and qualitative parameters (characters of mother tubers, vegetation cover, height of plants, number of leaves, number of true leaves, number of stems, number of stolons, lenght of first stolon, median diameter of first stolon, caliber of first tuber, final number of tubers per plant and final yield per plant). For the main agro-morphological characters, there were a great variation compared to the control Spunta. Challenger and Fabula showed the heighest caliber of mother tubers (49.16 mm), while heighest weight of seed tubers was determined on cv. Alegria (125.7 g). Among other characters, challenger produced the largest leaf area (9940.3 mm²). Panamera cultivar has considerable plant height (13.77 cm), the heighest number of leaves per plant (63.33) and also the heighest number of true leaves (48.48). Moreover, Panamera has the largest lenght of first stolon with 8.66 cm, (6.16 cm for Spunta). It has also the largest value of median diameter of first stolon with 2.17 mm and followed by Mondial (2.23 mm), Bellini (1.63 mm) and Liseta (2.01 mm). The difference among the cultivars in terms of median diameter of first stolon was statistically significant (P≤0.05). Liseta has the largest value of caliber of first tuber (37.4 mm), followed by Bellini (37.71 mm), while, Spunta has presented the lowest measures (13.36 mm). For final yield per plant, Bellini outyielded other cultivars with 0.96 kg per plant.

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