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 F v /F m , 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, F 0 , maximum fluorescence, F m , variable fluorescence, F v , F v /F m , T max (the time required to reach F m ), 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, F 0 , and T max . Nitrogen supply up to 10 g m -2 also had a positive effect on F m and F v , but above this rate it reduced F v /F m . Spunta had the highest Chl content, F m , F v , and F v /F m , but the lowest F 0 , whereas Sieglinde had the lowest Chl content, F v , F v /F m , and T max and the highest F 0 . The cvs. Igea and Daytona exhibited intermediate Chl fluorescence parameters. Chl content and T max decreased with increasing plant age, whereas F 0 , F m , and F v increased until complete canopy development and thereafter declined until crop maturity. Tuber and plant dry matter yield were significantly correlated with Chl content, F 0 , and T max . 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.
