Interactive effects of photoperiods and plant growth regulators on the development of flowering spikes and tubers in Chinese yams (Dioscorea opposita) cv. Ichoimo

The interaction between photoperiods and plant growth regulators [gibberellin A₃ 100ppm (GA), uniconazole P 25ppm(Uni), n-propyl dihydro-jasmonate 50ppm (PDJ), and salicylic acid 1000ppm (SA)] on the development of the main shoots, spikes, and aerial and new tubers in Chinese yam (Dioscorea opposita Thunb. cv. Ichoimo) plants was observed. The untreated control plants yielded the longest main shoots followed by GA, SA, PDJ, and Uni. Plant, treated with growth regulators, grew more under a 24-hr photoperiod than did those under an 8-hr photoperiod. GA treated plants, grown under the 24-hr photoperiod, developed spikes at a significantly lower node than that similarly treated plants grown under an 8-hr photoperiod; whereas the first flowering node on the control, GA, SA, Uni, and PDJ treated plants, grown under the 24-hr photoperiod, was equally higher than comparable plants, grown under the 8-hr photoperiod. More spikes per plants were initiated under the 24-hr photoperiod than on plants grown under an 8-hr photoperiod. GA treatment severely decreased the number of spikes under the 8-hr photoperiod. Aerial and new tubers developed earlier on plants under the short day than did those under constant light, but the new tubers on the latter treatment weighted more than did those on the former. The formation of aerial tubers was severely inhibited by GA but promoted by Uni under both photoperiods, while the growth of new tubers was significantly promoted by GA and significantly inhibited by Uni. PDJ and SA had no effect on the growth of aerial and new tubers.