TOMATO SEEDLING GROWTH, EARLINESS, YIELD, AND QUALITY FOLLOWING PRETRANSPLANT NUTRITIONAL CONDITIONING AND LOW-TEMPERATURES

'Sunny' tomato (Lycopersicon esculentum Mill.) seedlings were pretransplant nutritionally conditioned (PNC) in 1988 and 1989 with factorial combinations of N from 100 to 300 mg.liter-1 and P from 10 to 70 mg.liter-1. In 1988, all conditioned seedlings were exposed to 12 hours of 2C for eight consecutive nights before transplanting. In 1989, half of the conditioned plants were exposed to a low-temperature treatment of 8 days with 12-hour nights at 2C and 12-hour days in a warm greenhouse (19C/26C, night/day). In both years, as N PNC increased to 200 mg.liter-1, seedling growth increased. Increasing P PNC from 10 to 40 mg.liter-1 increased seedling growth, but only in 1988. In both years, P PNC did not affect yields. Low-temperature exposure in 1989 decreased seedling growth in comparison to those held in a warm greenhouse (19C/26C, day/night). In 1988, first harvest yields were not affected by N PNC; however, in 1989, as N increased to 200 mg.liter-1, early yields increased. In 1988, total yields increased with N PNC from 100 to 200 mg.liter-1 and in 1989 with N at 50 to 100 mg.liter-1, with no further increases from 100 to 200 mg.liter-1. Low-temperature exposure had no effect on earliness, yield, or quality. A PNC regime combining at least 200 mg N/liter and up to 10 mg P/liter should be used to nutritionally condition 'Sunny' tomato seedlings to enhance yield.