Effect of Winter-chilling Treatment on Flower Bud Induction in Young Pomelo Trees

Abstract

Two-year-old potted 'Tosa Buntan' pomelo (Citrus grandis (L.) Osbeck) trees on trifoliate orange (Poncirus trifoliata Raf.) rootstock grown in a plastic house were used in this study. The temperature of the plastic house was maintained at a maximum of 20°C during the day and 10°C minimum at night from November 1990 to mid-February 1991. On December 1990, a set of potted trees was transferred to each growth chamber which was kept at day/night temperature of 15°/5°C and 10°/10°C. A subgroup of these trees was exposed to these con-dition for 15, 30, 45, 60, and 75 days and then transferred to another growth chamber main-tained at 30°/25°C (day/night). On 1 December 1990, 15 January, and 15 February 1991, a set of potted trees was transferred directly without chilling from the plastic house to the 30°/25°C growth chamber.
No trees sprouted during the low temperature treatments. New buds sprouted early and more buds sprouted during subsequent exposure to 30°/25°C treatment as the low temper-ature was prolonged. The number of new shoots for 75-day exposure was greater at 15°/5°C than it was at 10°/10°C regimen and those kept in the plastic house. The number of inflores-cences, flower buds, and flowers increased for the 60-day and over exposures, but very few flowers developed after a 15- or 30-day exposure. The numbers of flower buds and flowers per node were 2.27 and 2.05, respectively, for a 75-day exposure under the 15°/5°C regi-men, whereas they were 0.81 and 0.76, respectively, in the 10°/10°C regimen. Sugar and carbohydrate contents in leaves increased while the N content decreased under prolonged low temperature treatments.