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The objective of this study was to determine the feasibility of CO2 enrichment and optimal radiation level for accelerating the rooting and growth of micropropagated Kalmia latifolia cuttings during the Stage IV acclimation period. Inch long microcuttings of the Kalmia cultivars `Elf' and `Carousel' shipped from a commercial micropropagation laboratory, were stuck in flats of peat, and place in a fogging chamber constructed to allow for the simultaneous experimental variation of CO2 level and either radiation level or photoperiod. Treatments consisted of a complete factorial arrangement of 2 levels of CO2 (ambient and 1200 ppm) and 3 levels of radiation (30, 98, and 158 μmoles/m2/sec). The experiment was repeated 6 times. For `Carousel' CO2 enrichment stimulated both shoot and root growth and either the high or medium light level was optimal depending on the experiment. CO2 enrichment also stimulated growth of `Elf' but results were less consistent from experiment to experiment. Similar experiments are in progress with Amelanchier and Lilac microcuttings.
To test the hypothesis that phytohormone production is related to mycorrhizae formation 29 isolates of ectomycorrhizal fungi have been evaluated for production of ethylene and auxin in pure culture and for their ability to form ectomycorrhizae with Pinus mugo. The fungi tested included a series of monokaryotic isolates of Laccaria bicolor and dikaryotic isolates of Amanita muscaria, Hebeloma crustuliniforme, L. laccata, L. proxima, Pisolithus tinctorius, Rhizopogon ellenae, and R. vinicolor. Inoculated root systems were rated for mycorrhizae formation, root/shoot ratio and root morphology. P. tinctorius isolates which formed abundant mycorrhizae produce no ethylene in vitro, but did produce the auxin IAA. L. bicolor isolates produced ethylene as well as auxins putatively identified as IAA, and IBA. Correlations between phytohormone production and mycorrhizogenicity will be presented.
American ginseng (Panax quinquefolium L.) contains pharmacologically active secondary compounds known as ginsenosides, which have been shown to be affected by both genetic and environmental factors. In this greenhouse experiment, we tested the hypothesis that ginsenosides would behave as “stress metabolites” and be associated with osmoregulation in response to drought stress. Two year-old seedlings, grown in 5-inch pots, were well watered for 40 days prior to the initiation of treatments. Plants in the drought stress treatment were watered every 20 days while the controls were watered every 10 days, and the experiment was terminated after 4 and 8 dry down cycles (80 days), respectively. Predawn leaf water potential and relative water content (RWC) of drought-stressed plants during a typical dry down cycle were lower than control plants. The diameter and weight of primary storage roots were decreased in the stressed treatment. The length of the main storage root and the longest secondary (fibrous) root were significantly increased by the drought stress treatment. Leaf chlorophyll content of drought-stressed plants was lower than controls. The osmotic potential of the drought-stressed ginseng was not lower than the control, indicating that ginsenoside is not involved in osmoregulation in response to drought stress. Furthermore, ginsenosides Rb1 and Rd, and total ginsenosides were significantly lower in primary roots of drought-stressed plants compared to control plants.
Woods cultivation of North American ginseng (Panax quinquefolium L.) can generate income for forest land owners and decrease collection pressure on wild populations of this increasingly scarce forest herb. For woods cultivation, supplemental calcium by soil application of gypsum (CaSO4 2H2 O) is often recommended, but the effects of this practice on soil characteristics, plant growth and quality of American ginseng are not well characterized. In a greenhouse pot culture experiment, 3-year-old seedlings were treated with 0, 1, 2, 3, or 4 Mt/ha gypsum and grown for 12 weeks. Gypsum application decreased soil pH slightly and elevated soil electrical conductivity and available soil calcium. Tissue levels of calcium were not affected by gypsum treatment but a significant increase in both shoot and root dry weight occurred. Total ginsenosides, which are the pharmacologically active components of ginseng, were increased slightly in roots but not in shoots of plants treated with 4 Mt/ha gypsum. Rb1, the most abundant ginsenoside in roots, was elevated in roots of plants treated with 3 Mt/ha gypsum. Ginsenoside Rg1 was elevated in shoots of plants treated with 2 Mt/ha gypsum. Regardless of gypsum treatment, qualitative differences (relative concentrations of different ginsenosides) between roots and shoots were observed.