Vegetable crops produced in the field from transplants for early harvest are exposed to various stressful conditions. Standard treatment for transplants before planting out is hardening, through lowering the temperature or less-frequent watering. This process launches several plant defensive mechanisms against stress. However, chilling must be adjusted to specific crop species or even cultivars, because their response to low temperature may be different. The aim of the present experiment was to determine the effect of transplant chilling on the morphology of broccoli inflorescences. The experiment was conducted in the years 2011–2012. Broccoli transplants were chilled for 1 week or 2 weeks at 6, 10 and 14°C. Control plants were exposed to 18°C. Bud diameter and bud stalk length of broccoli inflorescences were measured, as well as diameter and weight of mature heads. In response to longer transplant chilling period, in the following growing stages plants formed inflorescences with longer bud stalks compared to the non-chilled control. The same tendency was observed for bud diameter in inflorescences. The greatest diameter of buds was noted for plants exposed to 10°C in comparison to the control, with buds about 29% smaller in diameter. Mean diameter of mature heads was the lowest for control plants, while the widest was obtained from plants chilled at 6°C or 10°C for 2 weeks, depending on the year. Chilling of transplants positively influenced the weight of broccoli heads at harvest in most cases, and the heaviest heads were obtained as a result of transplant chilling at 6°C. Relationships between temperature and some parameters of broccoli heads were found and regression equations were created.

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