End-of-Day Light Quality Effects on Growth and Development of Watermelon Plants

Abstract

End-of-day (EOD) red (R) or far-red (FR) light treatments were used to study phytochrome-regulated growth and dry matter distribution in 2-week-old watermelon plants. Plants were exposed to low-intensity R or FR light for 15 min at the end of photoperiod for 9 consecutive days. End-of-day FR increased the petiole elongation in the first two leaves, which was accompanied by higher dry matter partitioning to the petioles after 3 days of treatments. However, total plant dry mass (above ground) in FR-treated plants increased significantly after 6 days of treatments. This indicates EOD FR regulated dry matter compensation among plant parts at the early stages of EOD light treatments, allowing plants to better adapt to the environment. Net CO2 assimilation rate in the second leaf of FR-treated plants also increased. Phytochrome involvement in these processes is suggested, since growth and dry matter distribution patterns were reversible when plants were treated with FR immediately followed by R.