PHOTOPERIOD EFFECTS ON FLOWERING AND SEED SETTING OF HYPERICUM PERFORATUM

The effects of clay length extension and night interruption on flowering responses of St John's Wort (Hypericum perforatum) plants were investigated. Field-grown plants were subjected to five different clay lengths (11, 13, 15, 17 and 19 h d(-1)) or night interruption for 70 days. Use results indicated that St John's Wort is a long-day plant requiring a critical day length of 15 hd(-1) for flowering induction. Both clay length extension (duration longer than 15 h) and night interruption, with artificial light (fluorescent lamps that delivered 30 mu mol m(-2) s(-1) photosynthetic photon flux density at plant height) were effective for flowering induction and seed setting. Day length extension or night interruption experienced by the maternal plant also affected the germination responses of the seeds produced. Plants that had received 19 h of day length treatment produced seeds with better germination responses. Night interruption with daylight type fluorescent lamps was also effective for producing relatively high quality seeds, although these seeds had slightly lower germination rates and longer mean germination time than seeds produced under 19 h of day length. Such a night interruption system could be considered for seed production of St John's Wort on a commercial scale.