Field experiments were conducted in Sicily (south Italy) to assess chlorophyll (Chl) fluorescence parameters in response of potato crop to nitrogen dose, to variation in genotype and in plant age, and to detect relationships between Chl content, fluorescence parameter Fv/Fm, and tuber yield. The experiment included five nitrogen doses (0, 10, 20, 30, and 40 g m-2) and four genotypes (Spunta, Sieglinde, Daytona, and Igea). Chl fluorescence parameters (initial fluorescence, F0, maximum fluorescence, Fm, variable fluorescence, Fv, Fv/Fm, Tmax (the time required to reach Fm), and Chl content were measured weekly between the appearance of the fifth and sixth leaves and the onset of plant senescence. A positive linear relationship was established between nitrogen supply and Chl content, F0, and Tmax. Nitrogen supply up to 10 g m-2 also had a positive effect on Fm and Fv, but above this rate it reduced Fv/Fm. Spunta had the highest Chl content, Fm, Fv, and Fv/Fm, but the lowest F0, whereas Sieglinde had the lowest Chl content, Fv, Fv/Fm, and Tmax and the highest F0. The cvs. Igea and Daytona exhibited intermediate Chl fluorescence parameters. Chl content and Tmax decreased with increasing plant age, whereas F0, Fm, and Fv increased until complete canopy development and thereafter declined until crop maturity. Tuber and plant dry matter yield were significantly correlated with Chl content, F0, and Tmax. Thus Chl fluorescence and content detect differences in the response of potato to N supply, can discriminate between genotypes, predict plant age, and yield performance under field conditions. and G. Mauromicale, A. Ierna, M. Marchese.