Cabbage is one of the most important cash crops which can contribute to food security. It is a cool season crop and its production maybe seriously impaired by bolting. Therefore, understanding cabbage bolting as affected by low temperature is vital for the sustainable production of this crop in South Africa. The objective of the study was to determine whether bolting in cabbage plants is triggered by low temperature during the seedling, cupping, early heading or mature head growth stages.
The research was conducted at the University of Pretoria s Experimental Farm and the Plant Science Complex. Walk-in growth chambers, glass houses, shade nets, incubators and the open field were used for conducting experiments in 2012 and 2013. Cabbage plants at different growth stages were exposed to different combinations of low (night) and high (day) temperatures. Night temperatures of 5 °C, 7 °C, 10 °C and 15 °C were used whilst 15 °C and 20 °C were used as day temperatures during the treatment phase. Night temperatures of 20 °C and day temperature of 30 °C were used for growing the plants after treatment. For Experiments 1 and 2, plants were transplanted into open field after treatment. A second field experiment was conducted separately to over-winter the plants. Plants were exposed to the same agronomic practices in the field. Harvesting for all experiments was carried out after plants reached full maturity. Parameters used for this research were head mass and length, core length, core width, and signs of bolting. The results of this study showed no signs of bolting on hybrid cabbage plants during the seedling and cupping growth stage, however, signs of bolting, such as inflorescence primordia and developing inflorescences, were found in leaf axils along elongating cores and apical buds, on early heading and mature heads. This showed that both, the early heading and mature head stages were receptive for induction to bolting. From this study, it can be recommended that in areas that may experience instant transition from cold winter temperatures to warm spring temperatures, over-wintering of susceptible cabbage cultivars should be avoided to minimise the effect of bolting in cabbage production.