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J.S. Ebdon, R.A. Gagne, and R.C. Manley

Turf loss from freezing injury results in costly reestablishment, especially with turfgrasses such as perennial ryegrass (Lolium perenne L.) having poor low-temperature tolerance. However, no studies have been conducted to investigate the relative importance of low-temperature tolerance and its contribution to turfgrass quality (performance) in northern climates. The objective of this research was to compare critical freezing thresholds (LT50) of 10 perennial ryegrass cultivars representing contrasting turf-quality types (five high- and five low-performance cultivars). Cultivar selection was based on turfgrass quality ranking (top and bottom five) from the 1997 National Turfgrass Evaluation Program (NTEP) trial conducted at the Maine (Orono) location. Ten freeze-stress temperatures (-3 to -21 °C) and a nonfrozen control (5 °C) were applied to 5-month-old plants. Acclimated (AC) plant material maintained in an unheated polyhouse during the fall and winter in Massachusetts was compared to nonacclimated (NA) plant material (grown at 18 °C minimum in a greenhouse). Low-temperature tolerance was assessed using whole-plant survival and electrolyte leakage (EL). Estimates of LT50 were derived from fitted EL and survival curves using nonlinear regression. High-performance cultivars were able to tolerate significantly lower freeze-stress temperatures indicated by less EL and greater survival compared to low-performance cultivars. The EL method had good predictive capability for low-temperature survival. Acclimated tissues and high-performance cultivars had significantly flatter EL curves and lower mortality rates. These results underscore the importance of selecting cold-tolerant perennial ryegrass genotypes for adaptation to northern climates.

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S. Bergeron, M.-P. Lamy, B. Dansereau, S. Gagne, S. Parent, and P. Moutoglis

While the majority of terrestial plants are colonized in soils by vesicular-arbuscular fungi (AM), that does not mean that these species can form a symbiosis with AM fungi in an artificial substrate under commercial production conditions. The purpose of this study was to identify those plants having a colonization potential. In Mar. 1998, 51 species and cultivars of ornamental plants were inoculated with two vesicular-arbuscular fungi (Glomus intraradices Schenk & Smith, and Glomus etunicatum Becker & Gerdemann; Premier Tech, Rivière-du-Loup, Quèbec). Periodic evaluations of colonization were done 5, 7, 9, 12, and 16 weeks after seeding. More than 59% of these plants tested were shown to have a good colonization potential with G. intraradices. Species belonging to the Compositae and Labiatae families all colonized. Species in the Solanaceae family showed slight to excellent colonization. Several species studied belonging to the Amaranthaceae, Capparidaceae, Caryophyllaceae, Chenopodiaceae, Cruciferae, Gentianaceae, Myrtaceae et Portulaceae families were not colonized. Root colonization with G. etunicatum was not detected on these species and cultivars during this short experimental period.

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S. Mantha, H. Desilets, J.-A. Rioux, S. Gagne, S. Parent, and P. Moutoglis

Two experiments with Malus domestica sp. were planted in 1997 at the Laval Univ. experimental farm located south of the St. Lawrence river near Quebec City. These experiments examined the association of the mycorrhizal fungus Glomus intraradices with Malus domestica sp. The first experiment compared the vegetative growth of `McIntosh' apple trees on M.106 rootstock in presence or absence of a commercial inoculum of G. intraradices (Premier Tech, Riviere-du-Loup, Quebec) under three levels of phosphorus fertilization (P) to the soil (0%, 50%, and 100% of the usual recommandation for this crop). After two seasons, all the treatments had better growth than the control (0% P without G. intraradices). The best treatment was achieved with 100% of the P associated with mycorrhizal inoculation. The second experiment compared the vegetative growth of three apple rootstocks Bud.9, M.26, and M.106, inoculated with G. intraradices under the same three P levels as the preceding experiment. Uninoculated rootstocks receiving the usual phosphorus fertilization served as control. Two roostocks, M.26 and M.106, increased growth with G. intraradices, while the third one, Bud.9, did not respond to the presence of mycorrhizal fungus.

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I. Nadeau, H. Desilets, S. Gagne, S. Parent, P. Moutoglis, and D. Robitaille

American ginseng (Panax quinquefolius) is a native plant of the deciduous forests of eastern North America. This highly valuable medicinal plant has been grown commercially for nearly a century in the field, under artificial shade sources, or in forests under mature trees. Wood-grown ginseng roots are highly similar to the wild ones, which increases their value. However, the time required to produce a marketable root is two to three times longer in the forest than in the field. In an attempt to reduce this time, a new technique has been developed to produce ginseng transplants destined for forest culture. Ginseng seedlings pre-treated with giberellic acid were sown in forest plots in a peat base culture medium ammended with an inoculum of the arbuscular fungi Glomus intraradices or G. etunicatum. The plantlets were grown for 18 weeks in greenhouse under shade cloth. The two Glomus spp. suceeded in colonizing the ginseng rootlets, developing the `Paris' mycorrhizal type, as previously reported for this plant. In addition, plantlets inoculated with G. etunicatum weighed 15% more than the control and were significantly more branched. The amount of P, K, and Mg in the roots was significantly higher in mycorrhizal ginseng plantlets.