Suitable night temperature conditions for reducing the acidity content in winter-harvested passion fruit
Passion fruit (Passiflora spp.) are native to southern Brazil and were introduced to Japan in the 1890s. They have been cultivated commercially since the 1940s. Passion fruit can be harvested twice in a year, in summer and winter. Winterharvested fruit display a much higher acidity than those harvested in summer; i.e., 5.3% in winter but only 2.2% in summer. High acidity in the fruit causes a reduction in their commercial value. It is important to reduce the acidity as much as possible before harvest. In the current experiment, the combined effect of a fixed day temperature of 30℃ and various night temperatures was analyzed using a growth chamber to identify suitable temperature conditions for sufficient reduction in acidity.
Experiments were performed in 2004, 2005, and 2006 using 2-year-old “Summer Queen” (P. edulis x P. edulis f. flavicarpa) passion fruit plants grown in a greenhouse at the Japan International Research Center for Agricultural Sciences (JIRCAS) on Ishigaki Island, Okinawa Prefecture. The plants were transplanted to 20-liter pots in July 2004. On November 15, 2005, supplemental lighting from 18:00 to 23:00 was started to promote floral induction. On January 3, 2006, when half of the experimental plants had started flowering, four plants were brought into each growth chamber and kept under temperature regimes of 30/30℃ (day/night), 30/25℃, and 30/20℃. The duration of the day temperature was 12 hours with artificial lighting. The other trees were left in the greenhouse with natural ventilation. Fruits were bagged to prevent them dropping to the ground, and harvested when they were mature and had dropped into their bag.
Fruit maturation was significantly enhanced at higher temperatures (Table 1). The fruit weight and juice percentage decreased with increasing temperature (Table 1). Peel color development was poor at high night temperatures (Table 1). The Brix value was not affected by night temperatures (Table 2). Titratable acidity (TA) was the lowest and the sugar/acid ratio was the highest under the 30/25℃ regime (Table 2).
The present study reveals that a temperature regime of 30/25℃ is the most effective in reducing the acidity of the winter crop of passion fruit. To be able to harvest low-acidity fruits in winter, it is recommended to keep the night temperature at around 25℃ by heating.
Tropical Agriculture Research Front, Japan International Research Center for Agricultural Sciences
- MIERUKA ID:001788
M. M. Macha, A. K. Chowdhury, K. Nomura, M. Ide and Y. Yonemoto (2006)： Effect of temperature regime and soil moisture level on fruit quality of ‘Summer Queen’ passionfruit (Passiflora edulis×P. edulis F. Flavicarpa). Japanese Journal of Tropical Agriculture（50: 70-75）
N. Kozai, I. Kataoka, T. Kondo, S. Amemiya, H. Higuchi, T. Ogata and Y. Yonemoto (2006): Effect of temperature regime on fruit quality in winter crop ‘Summer Queen’ passionfruit (Passiflora edulis×P. edulis F. Flavicarpa). Japanese Journal of Tropical Agriculture（in press）