Photoautotrophic Growth and Net Photosynthetic Rate of Sweet Potato Plantlets In Vitro as Affected by the Number of Air Exchanges of the Vessel and Type of Supporting Material

To produce high-quality sweet potato plantlets rapidly at low production costs, single nodal leafy cuttings of sweet potato (Ipomoea batatas (L.) Lam.) plantlets were cultured in vitro for 14 days on sugar- and phytohormone-free Murashige and Skoog (MS) liquid medium, at a photosynthetic photon flux (PPF) of 200 μmol · m−2 · s−1 and a CO2 concentration (v/v) of 1.8×10−3. A factorial experiment was conducted with two levels of the number of air exchanges of the vessel (NAE), 8.7-12.2 h−1 and ≥12.2 h−1, and two types of supporting material, vermiculite and Florialite (a porous material). The control treatment consisted of a photomixotrophic culture using a sugar- and NAA-containing agar MS medium with an NAE of 2.4 h−1. PPF and CO2 concentrations were the same as the photoautotrophic treatments. In comparison with the control treatment, the photoautotrophic treatments with NAE of 8.7-12.2 h−1 (MF treatment) and ≥12.2 h−1 (HF treatment) were, respectively, 2.2 and 2.8 times in dry weight, and 3.7 and 4.2 times in net photosynthetic rate, when Florialite was used. The survival percentages of the plantlets in the field were, respectively, 86% and 97% in the MF and HF treatments, and 35% and 46% higher than that in the control treatment. The plantlets cultured with Florialite showed greater growth, compared with those cultured with vermiculite. Photoautotrophic micropropagation system with high NAE and the use of porous supporting material can produce high-quality plantlets and make it possible to reduce production costs.