Factors Affecting Tolerance to Low Night Temperature Differ by Fruit Types in Tomato

Tolerance to low night temperature (LNT) can be a practical and economical target in tomato breeding programs for energy saving in greenhouses. This study was conducted to investigate the physiological and biochemical responses to LNT using four tomato accessions with cherry or large fruit types having LNT tolerance or sensitivity. The accessions were grown in two polyethylene film greenhouses with night temperature set-points of 10 and 15 °C for heating. LNT significantly reduced the plant height, and photosynthetic parameters were also lower in 10 than 15 °C among all accessions. Photosynthetic rate in 10 °C during the early growth period was reduced more in LNT-tolerant than -sensitive accessions. The numbers of flowers in 10 °C were significantly reduced in cherry but not in large fruit types. Fruit set in 10 °C significantly decreased in LNT-sensitive accessions of both fruit types, which was due to abnormal flower morphology. Proline accumulation patterns between 10 and 15 °C significantly differed between cherry and large fruit types as well as between LNT-tolerant and -sensitive accessions. Chlorophyll content at later growth stages in 10 °C was significantly higher in LNT-tolerant than -sensitive accessions in both fruit types. These results suggest that different tomato fruit types may have different mechanisms for LNT tolerance, possibly due to different proline accumulation patterns between cherry and large fruit types.