Response of two potato clones (S. tuberosum L.) to contrasting temperature regimes in the field

Two potato clones (S. tuberosum L.) were grown in the field under contrasting temperature regimes during the crop cycle. Differential growth and yield was observed in the clones studied. Differences in yield were due to the decreased proportion of tubers larger than 3.5 cm in length as well as to the differences in dry weight and percent of dry matter in tubers. Yield reductions per plant were 52 and 94% for Alfa and Herta, respectively, in the warmer regime compared with the cooler regime. Apparent photosynthesis rates measured in Herta were maximum (45 umol.m^?2.s^?1) during tuber filling. Stomatal resistance and apparent photosynthesis rate were reduced by high temperature, indicating mesophyllic inhibition of photosynthesis. Dark respiration was promoted by moderately high temperature and differed significantly between clones, with Herta showing the higher rates.