High-efficiency propagation of Chinese water chestnut [Eleocharis dulcis (Burm.f.) Trin. ex Hensch] using a temporary immersion bioreactor system

Several studies have reported different propagation methods for the Chinese water chestnut [Eleocharis dulcis (Burm.f.) Trin. ex Hensch]. To date, none of these methods have efficiently achieved large-scale plantlet production using minimal labor input. The present study investigated the propagation of Chinese water chestnut shoot tips derived from corm and creeping rhizomes in a temporary immersion bioreactor system (TIBS) compared with propagation using conventional semi-solid medium methods. We evaluated the regeneration capacity of the corm and creeping rhizome shoot tips of E. dulcis Guiti No. 2 sp. nov. and found that culturing under optimized TIBS conditions (15 min of immersion into nutrient medium every 8 h) produced the highest multiplication rate (36.5 times) and shoot-forming capacity (SFC, 68.9), and reduced the vitrification rate. Creeping rhizome shoot tips had slightly higher SFC than corm shoot tips; the highest shoot multiplication rate of 43.7 times in TIBS was obtained using Murashige–Skoog (MS) medium containing 4 mg L⁻¹ 6-benzylaminopurine and 0.5 mg L⁻¹ 1-naphthaleneacetic acid (NAA). These optimized conditions were applied to corm shoot tips of E. dulcis Guiti No. 1 var. nov., E. dulcis Guiti No. 2 sp. nov., and E. dulcis Guifengti No. 1 sp. nov. Root formation was observed during the shoot multiplication stage on semi-solid MS medium; however, root formation was not noted during the shoot multiplication stage in TIBS. While TIBS produced a higher multiplication rate and SFC indices, there were no significant differences in average number of shoots per explant between TIBS and semi-solid medium. We also evaluated the effects of different immersion frequencies and NAA concentrations on TIBS propagation of E. dulcis Guiti No. 2 sp. nov. shoot tips by measuring the rooting percentage, average number of roots (length ≥ 3 cm) per explant, maximum root length, and root-forming capacity (RFC). The results showed that the medium containing 2.0 mg L⁻¹NAA at the rooting stage produced the best-developed root systems with the highest rooting percentage, maximum root length, and highest RFC (75.8 %, 8.5 cm, and 3.8, respectively); it also reduced the immersion frequency. The optimized conditions produced plantlets that had a greater capacity to acclimatize after transfer to the greenhouse. E. dulcis Guiti No. 1 var. nov. plantlets had the highest survival rate (95 %), largest diameters, and highest number of creeping rhizomes. The results of this study demonstrate that TIBS is a reliable and efficient method for large-scale propagation of Chinese water chestnut plantlets.