Fruit Pungency of 'Shishito' Pepper as Affected by a Dark Interval in Continuous Fluorescent Illumination with Temperature Alteration

Abstract

The objective of this experiment was to elucidate the effects of a daily 6h-dark interval in continuous fluorescent illumination with temperature alteration to decrease the pungency level in sweet pepper 'Shishito' production. Plants were grown in a closed environment in half-strength "Otsuka-A" nutrient solution (EC 1.4 dS m^-1), whose pH was adjusted to 5.6, with a range of light intensity between 150 and 350 μmolm^-2s^-1, 800 ppm CO₂ enrichment and ambient humidity.
In experiment 1, seedlings were grown under a 18/6 hr (light/dark) cycle with corresponding temperatures of 28/20°C for 80 days (1-I period), 28/16°C for 60 days (1-II period) and 28/28°C (1-III period). In experiment 2, seedlings were grown either under continuous fluorescent illumination and a constant temperature of 28°C for 80 days (2-I period) or a 18/6 hr (light/dark) cycle with corresponding temperatures of 28/16°C (2-II period).
Green peppers were harvested at marketable size. Capsaicin was extracted from the fruit placenta with methanol and its concentration was determined with HPLC. Fruits under continuous fluorescent illumination and constant 28°C (2-I period) had fewer seeds and a higher concentration of capsaicin than greenhouse fruits harvested in summer. Capsaicin concentration decreased and the number of seeds increased with a daily 6h-dark interval in continuous fluorescent illumination with temperature alteration. These results suggest that there is a negative correlation between seed formation and capsaicin biosynthesis.