Flowering and bolting in carrot. II. Prediction in growth room, glasshouse and field environments

Rates of bolting and flowering in carrots cv. Chantenay Red Cored, measured as the reciprocals of days to first internode visibility and flower bud appearance respectively, were shown to relate linearly to a thermal time of vernalization derived from data obtained in controlled environments. Days elapsed from the end of vernalization to the start of visible bolting and flowering bore a curved relationship to thermal time of vernalization. The model curves also predicted closely the bolting and flowering responses of carrots to vernalization at different temperatures in controlled environments and under markedly different conditions in the field. Time taken from the end of vernalization to flowering and bolting decreased with increasing thermal time of vernalization, particularly between ca. 110 and 400°Cd. Vernalization beyond 400°Cd had less effect on the timing of these processes. The percentage of plants flowering increased asymptotically with increasing thermal time of vernalization up to ca. 400°Cd whereas shoot extension increased linearly up to ca. 650°Cd.