Low-level Irradiance during the Dark Period Prevents Photoperiodic-induced Tuberization of Potato

Abstract

The threshold irradiance during the dark portion of a photoperiod required to inhibit tuberization of potato (Solanum tuberosum L.) was investigated. Two cultivars of potato (cv. Norland, an early maturing variety; cv. Russett Burbank, a late-maturing variety) were grown using nutrient film technique hydroponics in separate tests within a walk-in growth chamber under a normally tuber-inductive photoperiod (12-h light/12-h dark). Light period photosynthetic photon flux (PPF) was provided by either daylight fluorescent lamps (providing 150 μmol·m–2·s–1 PPF) or a combination of daylight fluorescent and metal halide lamps (providing 300 μmol·m–2·s–1 PPF). The chamber was configured with vertically hung shadecloth and a pair of 15-W cool-white fluorescent lamps mounted at one end of the chamber to provide a range of low irradiance during the dark period. The low irradiance treatments averaged 3.65, 0.43, 0.06, and <0.01 μmol·m–2·s–1 PPF for the entire 12-h “dark” period. Results showed that tuberization occurred around 23 DAP, regardless of cultivar or light period PPF for plants grown with 0.06 and <0.01 μmol·m–2·s–1 PPF during the dark period. Tuberization also occurred at around 30 DAP for cv. Norland grown with 0.43 μmol·m–2·s–1 PPF during the dark period. No tubers were formed for either cultivar grown with 3.65 μmol·m–2·s–1 PPF during the dark period. These results indicate that light levels <0.43 μmol·m–2·s–1 PPF do not influence photoperiodic induction of tuberization in potato.