Tolerance of carrot seeds (Daucus carota L.) to heat treatments that could eradicate seedborne pathogens was investigated. Germination and emergence of seedlings from seeds treated in hot water at 35, 40, 45, 50, or 55C from 4 to 20 min were not affected, but seeds treated at 60C for 8 min or more were affected adversely. At 45 and 50C, treatment durations as long as 48 min did not affect emergence, but greater than 20 min at 55C reduced emergence. Simmilar results were obtained when seeds were treated at the same temperatures in water containing 1.1% sodium hypochlorite (NaOCl). Emergence of seeds treated in hot water or 1.1% NaOCl and planted within 5 days generally was similar to that of treated seeds stored for 90 days at 20C in 60% RH before planting. Any existing differences were small and not clearly related to temperature-duration treatment combinations. Percent emergence from seeds of 19 out of 25 hybrid cultivars treated at 50C for 15 min was reduced by an average of 2.9%, but differences for untreated seeds ranged from - 13.3% to + 4.8%. Emergence from hot water-treated seeds was reduced after 6 weeks of storage at 70% and 80% RH, but not at 20% to 60% RH. Prolonged treatment and the higher temperatures were particularly effective in reducing populations of seedborne Alternaria dauci.
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