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

Characterization of the North American ginseng (Panax quinquefolius L.) inf lorescence, the floret abscission zone, and its stimulation by ethylene wer e undertaken to gain insights into the potential for floret abscission indu ction as a replacement for the industry practice of expensive manual remova l of the inflorescence. In each of 3 years, peduncle length of 3-year-old c ultivated ginseng inflorescences increased rapidly in June, reaching maxima l values of 140-180 mm. During this period, seed head diameter also increas ed 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 reveale d development of the floral primordia first at their periphery and progress ing centripetally. Stamen initials were seen as a pentamerous whorl just un der 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 fl oral apices had already formed constriction zones between the flower and th e pedicel, indicating the position of the abscission zone. Length of time t o ethylene-induced abscission zone formation was less than 24 h in 3-year-o ld ginseng harvested on July 23, 1997. The abscission threshold for ginseng berry drop was in the range of 10-100 muL.L-1 ethylene.