Effects of Light Wavelength on Daughter Cladode Growth and Quality in Edible Cactus Nopalea cochenillifera Cultured in a Plant Factory with Artificial Light

Abstract

Abstract In this study, we investigated the effects of different-colored light-emitting diodes (LEDs) on the growth and quality of daughter cladodes of the edible cactus Nopalea cochenillifera. Cladodes were cultured hydroponically using the deep-flow technique under red, blue, or a combination of red and blue, or red, blue, and green light in an enclosed-type plant factory. We found that daughter cladodes developed from the mother cladodes in all the treatments, despite pH of the nutrient solution drastically decreasing over time. However, the elongation growth rate of the first daughter cladodes and the number of daughter cladodes produced were highest under red light and lowest under blue light, indicating that blue light suppresses daughter cladode development. The total fresh weight (FW) of the daughter cladodes emerging from a single mother cladode was also lowest under blue light. However, the average FW of the daughter cladodes was the highest under blue light, or under simultaneous irradiation with red and blue light. The number of spines, which is an undesirable characteristic in edible cacti, was significantly lower under red light than under blue light, while the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of the daughter cladodes was the highest under blue light or under simultaneous irradiation with red and blue light. Our results show that light wavelength has a strong effect on daughter cladode development in N. cochenillifera, so controlling the light environment represents an effective approach for improving the growth and quality of this edible cactus.