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Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes (TU-82-155 and NCC-58) were grown hydroponically and subjected to a temporary loss of lighting in the form of 14 days of prolonged darkness compared with a lighted control under standard daily light periods to determine the impact on growth responses and storage root yield. Vine cuttings of both genotypes were grown in rectangular channels. At 65 days after planting, lights were turned off in the treatment chambers and replaced by a single incandescent lamp, providing between 7 and 10 µmol-m-2·s-1 photosynthetic photon flux (PPF) for 18 hours, and the temperature lowered from 28/22 °C light/dark, to a constant 20 °C. Plants remained under these conditions for 14 days after which the original light level was restored. Growth chamber conditions predark included, a PPF mean provided by 400-W metal halide lamps, of 600 ± 25 pimol·m-2-s-1, an 18-hour light/6-hour dark cycle and a relative humidity of 70% ± 5%. The nutrient solution used was a modified half-Hoagland with pH and electrical conductivity (EC) maintained between 5.5-6.0 and 1000-1200 µS·cm-1, respectively, and was adjusted weekly. Storage root number and fresh weight were similar regardless of treatments. Plants exposed to prolonged darkness produced 10.5% and 25% lower fibrous root fresh and dry mass, respectively, but similar foliage yield and harvest index (HI). 'NCC-58' produced an average of 31% greater storage root yield than that of 'TU-82-155' but the number of storage roots as well as % dry matter (%DM) were similar. 'NCC-58' also produced 31% greater fibrous root dry weight, whereas 'TU-82-155' produced a 44% greater HI. The significant interaction between prolonged darkness and cultivars for %DM of the storage roots showed that DM for 'TU-82-155' was 18.4% under prolonged darkness and 17.9% in the light. That for 'NCC-58' was 16.4% under prolonged darkness compared with 19.4% (14.8% greater) for plants that were not subjected to prolonged darkness. The evidence that there were no adverse impacts on storage root yield following the exposure to prolonged darkness suggests that the detrimental effects were below the detectable limits for these cultivars in response to the short perturbation in the available light and that sweetpotatoes would be hardy under short-term failure situations. [ABSTRACT FROM AUTHOR]

Growth chamber experiments were conducted to evaluate the effect of irradiance and daily light period on storage root yield and leaf elemental concentration of two sweetpotato cultivars grown hydroponically by use of the nutrient film technique (NFT). Stem cuttings (15 cm) of cv. Whatley/Loretan and Georgia Jet were grown in N FT channels (0.15 x 0.15 x 1.2 m) in reach-in growth chambers under light period/irradiance combinations of 18 h: 300 µmol·m-2·s-1 or 9 h: 600 µmol·m-2 ·s-1photosynthetic photon flux. Temperature was 28/22 °C fight/dark with a relative humidity of 70% ± 5%. Storage root and foliage yields were greater in both cultivars exposed to a longer daily light period and lower irradiance. The main effect of cultivar indicated that storage root yield was significantly greater among plants of 'Whatley/Loretan' compared with that of 'Georgia Jet', whereas foliage yield was similar between cultivars. Leaves of plants grown under longer daily light period and lower irradiance had significantly lower concentrations of all elements, nitrogen, phosphorus, potassium, calcium, magnesium, manganese, iron, calcium, boron, and zinc, except for calcium, manganese, and boron. There were no significant differences in leaf elemental concentration between cultivars. Thus, a longer daily light and lower irradiance enhanced biomass production of sweetpotato but reduced leaf elemental concentration probably because of a "dilution" effect. [ABSTRACT FROM AUTHOR]