Temperature, light and the tomato

In good illumination, six tomato varieties all responded to an increase in day or/and night temperature by faster stem and fruit growth, earlier but smaller fruit yield with fewer fruits in shorter and lighter clusters, and a reduction in root, stem and leaf weight. Optimum temperatures for moderate growth and high fruit yield were 20°-23° C during the day and 11°-17° C during the night. The night temperature should be at least 6°C lower than during the day.

In poor illumination, plants responded to an increase in light intensity or day length by higher dry weight and leaves that were less thin and darker green; leaf dry weight increased more than leaf area. Cluster size and consequently yield was the first feature to suffer considerably by light reduction. Extra artificial light in winter before planting out gave faster growth and sturdier plants which flowered and fruited earlier than controls. The less the illumination, the more important the correct day and night temperatures. Emphasis was laid on balance between vegetative and generative growth, which was determined by the ratio of light and temperature, which in itself determined the balance between photosynthesis, and growth and respiration.