INVOLVEMENT OF UV RAYS IN SWEET CHERRY FRUIT COLORATION DURING MATURATION

To investigate the lighting conditions for fruit coloration during maturation, UV and white fluorescent light sources were used to artificially illuminate the detached fruit of several cultivars at different stages of maturity. The detached fruit were wrapped with plastic film and illuminated for 48 h or kept in the dark at 20°C. In ‘Satohnishiki’ fruit collected at the mid stage of maturation (before color changes began), UV-A at 2.35 W/m² greatly enhanced the red coloration compared to the dark control. White light illumination at 15 μmol/m²/s, however, hardly affected fruit coloration. White light did not have any synergistic effect on fruit coloration even when combined with UV-A. UV-B illuminated at 2.37 W/m² caused discoloration of the skin. Although ‘Napoleon’ and ‘Takasago’ (‘Rockport Bigarreau’) responded to these illuminating conditions similarly to ‘Satohnishiki’, these cultivars seemed less sensitive than ‘Satohnishiki’. On the other hand, with ‘Seneca’, coloration proceeded even in the dark and reached to the same level as under the UV-A illumination.
UV-A stimulation of red coloration in ‘Satohnishiki’ fruit occurred at any stage of maturity. However, the effectiveness was relatively less during early stages of maturation. UV-A illumination also was effective in the coloration of fruit having poor color even at later stages of maturation. These results suggest that the coloration of fruit in the blush-skinned cultivars largely is influenced by the existence of UV rays.