Effect of Partially UV-blocking Films on the Growth, Yield, Pigmentation, and Insect Control of Red Amaranth (Amaranthus tricolor)

Abstract

Red amaranth (Amaranthus tricolor) was grown in tunnels covered with partially UV-blocking films (<340, <350, <360, and <400 nm) for five weeks after sowing, and plant growth, anthocyanin concentration, and insect burden were compared with those of UV-transmitting films and outdoors. The values of plant height, stem cell length, leaf area, and fresh weight were higher in the plants grown under higher UV-blocking conditions, while the plant dry weight was greater under lower UV-blocking conditions due to the lower dry matter percentage under higher UV-blocking conditions. The red color of the upper leaves became lighter as the UV-blocking rate increased, while there was no such distinct difference in either the lower leaves or stem. Anthocyanin concentrations of both the stem and leaves of the plant apex were significantly lower under UV-blockings than under UV-transmitting conditions and outdoors, but there was almost no significant difference among different UV-blocking rates. Yellow and blue sticky traps were also suspended at the center of the tunnels, and twelve insects were trapped during the experimental period. The maximum invasion by insects and feeding damage of the seedlings were observed outdoors, followed by plants grown under UV-transmitting conditions. Partially UV-blocking conditions significantly reduced invasion by insects and feeding damage of the seedlings compared to outdoors and under UV-transmitting conditions, but there was no significant difference among different UV-blocking rates. The number of herbivores tended to decrease as the UV-blocking rate increased, while that of predators was little affected by the UV-blocking rate. Our results showed that partially UV-blocking conditions were as effective as fully UV-blocking conditions, especially for controlling some herbivores such as aphids and white fly, and also for maintaining an advantageous balance between herbivores and predators. On the other hand, anthocyanin pigmentation of higher plant parts was often inhibited under UV-blocking conditions.