Physiological responses to chilling in cultivars of processing tomato released and cultivated over the past decades in Southern Europe

Six processing tomato seedlings, representative of cultivars widely cultivated over the last 80 years in Southern Europe, were compared to assess the physiological responses to chilling. Low temperature stress was applied for 24 h (1 °C, day and night). PEARSON, the oldest cultivar, reported the highest values of chlorophyll content both using DUALEX (ChlDX = 23.11) and SPAD (ChlSPAD = 35.27) and nitrogen balance index (NBIDX = 29.62) measured with DUALEX, before chilling stress. The cultivar E6203 was the least sensitive to chilling with the highest value of maximal photosystem II (PSII) efficiency (Fv/Fm2 = 0.64) at recovery and visual regrowth score (VS3 = 4.0) at regrowth period. As regards chilling tolerance in terms of maximal PSII efficiency, few differences were observed among the cultivars, apart from C33, that was the most sensitive. On the other hand, a better regrowth was recorded in the modern ones. Strong correlations were found between the different parameters investigated both before (SPAD and DUALEX) and after the chilling stress (maximal PSII efficiency, SPAD and electrolyte leakage). SPAD values at regrowth were shown to be a good indicator of tomato chilling status at regrowth period. Analysis of genetic similarity based on microsatellite markers clearly discriminated modern and old varieties according to the year of release. This information could be useful in breeding programs for new cultivars suitable for early transplant, when chilling injury can happen.