Vesicular–arbuscular mycorrhizal associations of American ginseng (Panax quinquefolius) in commercial production

Abstract

Panax quinquefolius L. (American ginseng) roots collected from 1st year seedlings and 3-year-old plants on three commercial farms were colonized by vesicular–arbuscular mycorrhizal (VAM) fungi. Roots collected from ginseng plants in a managed maple–beech woodlot were also colonized by VAM fungi. Fungal hyphae entered roots either directly through root hairs or by forming appressoria on the surface of epidermal cells from which penetration hyphae formed. Hyphae colonized roots by passing intracellularly through cortical cells. Hyphal coils, from which arbuscular branches formed, were typical of the Paris-type of VAM association. The extent of colonization by hyphal coils and by arbuscules varied between 1-year-old and 3-year-old plants and among farms. The seasonal maxima for colonization differed among combinations of farms and plant age-classes in such a way as to suggest that a significant degree of the variability was due to characteristics of the individual seed beds. Over the season, we saw earlier development of hyphal coils that was only later exceeded by production of arbuscules; this pattern is consistent with the Paris-type morphology observed, in that arbuscule branches develop from hyphal coils. However, the speed at which arbuscules developed at some points in the season was so great that at those times the transition from newly formed hyphal coils to arbuscules must be extremely fast. Vesicles were rarely found in any root samples examined. Keywords: ginseng, Panax quinquefolius, vesicular–arbuscular mycorrhiza, commercial farms.