Abstract
In order to improve the quality of tomato nursery plants in high-temperature periods, we investigated the effect of root-zone cooling of the potted seedlings on growth, establishment, and subsequent fruit yield. We utilized cold water passed through a heat exchange pipe which contacted the pot surface of tomato seedlings to reduce the growing medium temperature. The root growth was enhanced by continuous (24 h) cooling, while both shoot and root growths were enhanced by daytime (7:00~19:00) cooling. On the other hand, night-time (19:00~7:00) cooling repressed shoot growth. Enhanced root growth by root-zone cooling improved plant establishment. Moreover, daytime root-zone cooling during the pot seedling stage increased the subsequent fruit yield. Daytime root-zone cooling for 8 h (9:00~17:00) had nearly the same effects as those for 12 h (7:00~19:00). Based on the above findings, under this experimental condition, tomato seedlings with a high yield potential in a low-node-order pinching system at a high planting density could be produced by cooling the center of the medium by 3~4°C during particularly high-temperature hours.
