Cyclic cold stresses before transplanting influence tomato seedling growth, but not fruit earliness, fresh-market yield, or quality

Tomato seedlings (Lycopersicon esculentum Mill. 'Sunny') were exposed to cyclic cold stress at 2 ± 1C, then to 29 ± 6C in a greenhouse before being transplanted to the field. Cold-stressed seedlings were transplanted when the risk of ambient cold stress was negligible. In the first year of a 2-year study, transplants were exposed to 2C for 3, 6, or 12 hours for 1, 3, or 6 days before field planting. In the second year, transplants were exposed to 2C for 6, 12, or 18 hours for 4, 7, or 10 days before field planting. In the first year, cold stress generally stimulated increases in seedling height, leaf area, and shoot and root dry weights but decreased chlorophyll content. In the second year, all seedling growth characteristics except leaf area and plant height were diminished in response to longer cold-stress treatment. In both years, earliness, total productivity, and quality were unaffected by any stress treatment. Therefore, cold stress occurring before transplanting has a negligible effect on earliness, yield, or quality. Tomatoes are established in coastal South Carolina in the field by transplanting . The major benefit of transplant use is earlier production. However, stresses during the stand-establishment phase may delay plant development and may negate any benefit to earliness. Normally, many successive hand-harvests are re- quired for acceptable yields. Because of high labor costs, meth- ods to reduce harvest costs are desired. It is imperative, therefore, that transplanted tomatoes become established rapidly and uni- formly to ensure maximum yield with few harvests. To time the production to maximize returns, tomatoes in coastal South Carolina are transplanted near the last killing frosts. In some cases, late-season frosts may kill newly planted fields, or periods of cold weather may stagnate growth and establishment. It is not known whether cold stress occurring during the seedling phase retards growth and development over the course of the season. Previous studies with cotton (Christiansen and Thomas, 1969), carrots and lettuce (Currah, 1978), red beets (Hegarty and Thompson, 1974), and onions (Henriksen, 1978) have con- firmed that stress incurred early in crop development reduced yield. Little research has been done on the long-term effects of short-term stresses on transplanted vegetable crops. Customary methods of reducing stress in the field may in- volve proper acclimation of transplants by withholding water or exposing the transplants in holding areas to low (Wheaton and Morris, 1968) or high temperature extremes. However, these techniques may inhibit tomato growth and development. The earliness of hardened tomato transplants in cold frames can be reduced in contrast to nonhardened plants (Brasher and West- over, 1937; Porter, 1936). Brasher (1941) stated that any method used to harden young tomato plants slows their field perform- ance permanently, probably decreasing the yield in proportion to the severity of the hardening treatment. However, gradual exposure of tomato seedlings to low temperatures can increase the ability of seedlings to tolerate further cold stresses (Shen