The North American ginseng inflorescence: development, floret abscission zone, and the effect of ethylene

Abstract

Characterization of the North American ginseng (Panax quinquefolius L.) inflorescence, the floret abscission zone, and its stimulation by ethylene were undertaken to gain insights into the potential for floret abscission induction as a replacement for the industry practice of expensive manual removal of the inflorescence. In each of 3 years, peduncle length of 3-year-old cultivated ginseng inflorescences increased rapidly in June, reaching maximal values of 140–180 mm. During this period, seed head diameter also increased to about 35 mm, while seed head fresh mass increased in July and August to 6.5–8.0 g. Flowering in 1996 and 1997 began in the last 2 weeks of June and lasted through July, with open flowers never exceeding 35%. Anatomical studies and manual dissection of 1- and 3-year-old perennating buds revealed development of the floral primordia first at their periphery and progressing centripetally. Stamen initials were seen as a pentamerous whorl just under the petal primordia, and the characteristic inferior ovary initiated as a slight depression at the centre of the floral meristem. Sections through 3-year-old inflorescences harvested on May 23, 1996, showed that distal floral apices had already formed constriction zones between the flower and the pedicel, indicating the position of the abscission zone. Length of time to ethylene-induced abscission zone formation was less than 24 h in 3-year-old ginseng harvested on July 23, 1997. The abscission threshold for ginseng berry drop was in the range of 10-100 µL·L–1 ethylene.Key words: anatomy, flowering, Panax quinquefolius, perennating bud.