Manipulation of flowering in cineraria. III. Cardinal temperatures and thermal times for vernalization

SummaryEffects of temperatures and durations of temperature treatments on flower induction were studied in cineraria cv. Cindy Blue grown in controlled environments. The earliest flower induction, recorded as the fewest leaves below the flower, was observed as 16–17 leaves initiated in non-juvenile plants that had been chilled at 5–7°C for 3–5 weeks as compared with 30–33 in plants grown throughout at 24°C. Plants demonstrated a true quantitative vernalization response in that flowering was delayed but not prevented by higher temperatures and further leaves were initiated below the flower after chilling had ended. The rate of progress to flower induction, measured as the reciprocal of leaf number below the flower, was shown to relate linearly to temperature. This enabled the base, optimum and maximum temperatures for vernalization to be derived respectively as –0.3, 5.9 and 15.8°C, where the base temperature corresponded to the rate at which the unvernalized plants would progress to flower induction. Rate...