VESICULAR-ARBUSCULAR MYCORRHIZAL ASSOCIATIONS OF AMERICAN GINSENG (PANAX-QUINQUEFOLIUS) IN COMMERCIAL PRODUCTION

Panax quinquefolius L. (American ginseng) roots collected from Ist yea r seedlings and 3-year-old plants on three commercial farms were colon ized by vesicular-arbuscular mycorrhizal (VAM) fungi. Roots collected from ginseng plants in a managed maple-beech woodlot were also coloniz ed by VAM fungi. Fungal hyphae entered roots either directly through r oot hairs or by forming appressoria on the surface of epidermal cells from which penetration hyphae formed. Hyphae colonized roots by passin g intracellularly through cortical cells. Hyphal coils, from which arb uscular branches formed, were typical of the Paris-type of VAM associa tion. The extent of colonization by hyphal coils and by arbuscules var ied between 1-year-old and S-year-old plants and among farms. The seas onal maxima for colonization differed among combinations of farms and plant age-classes in such a way as to suggest that a significant degre e of the variability was due to characteristics of the individual seed beds. Over the season, we saw earlier development of hyphal coils tha t 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 arbus cules developed at some points in the season was so great that at thos e times the transition from newly formed hyphal coils to arbuscules mu st be extremely fast. Vesicles were rarely found in any root samples e xamined.