Effect of early season day/night temperatures on vegetative and reproductive growth of cultivar ‘Tosa Buntan’ pummelo ( Citrus grandis (L.) Osbeck)

Abstract

The effect of eariy season day/night temperatures on vegetative growth, flowering and fruiting of 2-year-old potted cultivar ‘Tosa Buntan’ pummelo trees on trifoliate orange rootstock was investigated. The growth chamber day/night (12 h/12 h) temperature regimes were 20/5°C, 20/10°C, 20/15°C, 25/10°C, 25/15°C and 25/20°C, from early December 1988 to early April 1989. The higher day/night temperatures shortened the time to shoot initiation and flowering, with day temperature having a stronger effect than night temperature. The trees from the 25°C day temperature regime produced fewer new shoots, leaves and flowers, but had increased shoot length, leaf size and fruit set compared to those grown at 20°C. Fruit from the 25°C day temperature regime were markedly larger, and had a more pyriform shape, thicker peel, higher total soluble solids and lower juice citric acid contents in early December 1989. There were no significant differences in chlorophyll, N, P, K, Ca, Mg and carbohydrate contents in new leaves at the termination of temperature treatments.