Addition of green light improves fruit weight and dry matter content in sweet pepper due to greater light penetration within the canopy

Abstract

The use of artificial light to supplement natural light is essential for successful greenhouse winter production in regions with low natural sunlight to meet the increasing consumer demand for fresh vegetables. Traditionally, high-pressure sodium lights have been used. However, light-emitting diodes (LEDs) are receiving substantial interests as they have higher photon efficacy and allow for spectral manipulation. There has been a lot of research on red and blue LED light but green light has not been studied to the same extent due to its perceived lower photosynthetic efficiency. However, green light can penetrate deep into canopy and thus could improve light intensity and photosynthesis deep within canopy. Therefore, we investigated the response of sweet pepper (Capsicum annuum) plants cv. ‘Eurix’ and ‘Gina’ under LED lighting with different percentages of green light (red/blue with 0 (control), 12, 24 and 43% green) at a light intensity of 175 µmol m−2 s−1 during a 6-month winter production period in Ontario, Canada. Gina plants grown under 12% green light had longer internodes than those grown under a red/blue control. The tenth leaves of Eurix plants grown under all green light treatments had higher chlorophyll value than the red/blue control. Leaves of both cultivars grown under the green light treatments tended to have slightly higher photosynthetic rates. The fruit weight (g fruit−1) increased by 2–15% depending on cultivars and percentages of green light, and fruit dry matter content linearly increased with increasing percentages of green light. Notably, the light intensity deep within the canopy (3 m from the tip) in treatments with green light was 43–158% higher. Thus, the increased light deep within the canopy with the green light treatments improved pepper fruit weight and dry matter content through increased photosynthesis and carbon export.