Growth and development responses of ornamental gingers to photoperiod

Rhizomes of Curcuma alismatifolia 'Chiang Mai Pink' and tissue cultured plants of C. cordata, C. petiolata 'Emperor', C. thorelii, Kaempferia sp. 'Grande', Siphonichilus decora and S. kirkii were grown in a greenhouse under 8-, 12-, 16-, and 20-hour photoperiods. All plants grown under the 8-hour photoperiod became dormant over a 15 week time period. After 90 days, most ginger species grown under the 16- and 20-hour photoperiods were taller than those grown under 8 and 12 hours. A larger number of unfolded leaves was indicated for all ginger species grown under 16- and 20-hour photoperiods compared to those grown under 8- and 12-hour photoperiods except for C. thorelli. The percentage of unfolded leaves as determined by quartile indicated similar results. The number of underground rhizomes of C. alismatifolia, C. cordata, and C. petiolata increased when plants were grown at 16 and 20-hour photoperiods. The number of tuberous-roots (t-roots) increased as photoperiod decreased below 16 hours for C. alismatifolia, C. cordata, C. petiolata, Kaempferia sp. and S. kirkii. Siphonichilus decora produced no t-roots while C. thorelii produced the most t-roots at 16 hours. Vegetative growth of gingers grown in this study, except for C. thorelii, was maintained and increased at photoperiods of 16 and 20 hours. Photoperiods of 8 and 12 hours induced dormancy and t-root production of most of these gingers.