Article ID: OKD-023
The effects of temperature and light on photosynthetic, chlorophyll fluorescence characteristics under high temperature in the passion fruits ‘Summer Queen’ (P. edulis × P. edulis f. flavicarpa) and ‘Ruby Star’ (P. edulis × P. edulis f. flavicarpa) were examined. Photosynthetic rates of both cultivars markedly and linearly increased up to 300 μmol·m−2·s−1, and less markedly increased from 300 to 1500 μmol·m−2·s−1 under several light conditions. Their light saturation points were recorded at around 1200 μmol·m−2·s−1 photosynthetic photon flux densities (PPFD). Regarding the relationship between temperature and photosynthesis, the maximum value of the apparent photosynthetic rate of ‘Summer Queen’ was observed at 30°C, and it was lower at both lower and higher temperatures. In ‘Ruby Star’, on the other hand, the maximum value was observed at 20 to 30°C, and this decreased at 35 and 40°C. The gross photosynthetic rate of ‘Summer Queen’ decreased over 30°C whereas in ‘Ruby Star’, it decreased to a lesser extent. The transpiration rate of ‘Ruby Star’ was higher than that of ‘Summer Queen’ at 40°C. Dark respiration increased from 20 to 40°C in both cultivars. Concerning chlorophyll fluorescence characteristics, ‘Summer Queen’ showed high-temperature injury at 40°C and all parameters were significantly decreased at 45°C. On the other hand, Fv/Fm showed only a slight decrease at 45°C in ‘Ruby Star’. These results indicate that ‘Summer Queen’ is susceptible to heat stress and that the range of its optimal temperature for photosynthesis is lower than ‘Ruby Star’.
