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F. Ponton, Y. Piché, S. Parent, and M. Caron

The horticultural Boston fern [Nephrolepis exaltata (L.) Schott cv. Verona] was micropropagated in vitro using commercial techniques. Rooted plantlets were transferred into pots containing one of three test substrates made of peat and vermiculite and subsequently inoculated with one of two species of Glomus. Survival of uninoculated control plants growing on a black peat-based mix was less than that on a brown peat-based mix. Vesicular-arbuscular mycorrhizal (VAM) inoculation significantly increased survival on the former, but not the latter, substrate. The growth of roots was enhanced in brown peatmoss, but VAM colonization was faster with black peatmoss. Compared to uninoculated controls growing under the same fertilization regime, inoculated plants had significantly higher frond P and N concentration and also showed better frond and root growth. On a growth-increment basis, our results suggested that the brown peat-based mixed was more suitable for fungal activity and fern growth.

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F. Ponton, Y. Piché, S. Parent, and M. Caron

Rooted plantlets of in vitro micropropagated Boston fern [Nephrolepis exaltata (L.) Schott var. Whitmanii] were transferred to pots containing a brown peat-based mix and simultaneously inoculated with one of four species of Glomus. Glomus intraradices and G. clarum formed rapid and extensive infection in Nephrolepis exaltata roots, while Glomus vesiculiferum and G. versiforme showed a significantly slower rate of infection. The high P fertilized control performed better than the other treatments, except in the number of fronds, which was similar. From the four mycorrhizal treatments, plants inoculated with Glomus vesiculiferum showed the most significant increase in growth when compared with the low P fertilization control. These results led us to re-examine vesicular-arbuscular mycorrhizal inoculation as an alternative to higher P fertilization in horticultural Boston fern production.

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L.E. Parent, A. Karam, and S.A. Visser

Compositional nutrient diagnosis (CND) norms were computed from a diagnosis and recommendation integrated system (DRIS) databank as means and sds of CND multinutrient ratios and CND factors characterizing the high-yielding subpopulation of greenhouse tomato (Lycopersicon esculentum Mill.) plants during the 3- to. 8-cluster developmental stages. A CND multinutrient ratio is a row-centered logratio corrected for the bounded-sum constraint to 100% of all components, including a filling value between known components and 100%. CND multinutrient ratios for N, P, K, Ca, and Mg were reduced to three dimensions by principal component analysis (PCA). Varimax-rotated factors–(N-K-Ca+), (Ca+Mg-), and (P)—were designated as contrasts describing nutrient status and equilibria in diagnostic tissues. CND nutrient indexes for N, P, K, Ca, and Mg were highly correlated with their DRIS counterparts (r = 0.964 to 0.987), using 20 independent observations. Since CND is compatible with PCA, CND could expand DRIS to a multivariate diagnostic approach projecting structured information on nutrient data into a Euclidean space. A critical sphere specific to a developmental stage could delineate the high-yielding subpopulation for diagnostic purposes. The critical radius defined using a probabilistic approach to capture the high yielders should be validated with independent fertilizer experiments.

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H. Wang, S. Parent, A. Gosselin, and Y. Desjardins

Micropropagated plantlets of Gerbera jamesonii H. Bolus ex Hook. F. `Terra Mix', Nephrolepis exaltata (L.) Schott `Florida Ruffles', and Syngonium podophyllum Schott `White Butterfly' were inoculated with two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices Schenck and Smith and G. vesiculiferum Gerderman and Trappe. They were potted in three peat-based media to determine the effects of mycorrhizal peat substrate on acclimatization and subsequent growth of micropropagated plantlets under greenhouse conditions. Symbiosis was established between the three ornamental species and VAM fungi within 4 to 8 weeks of culture in the greenhouse, but not during acclimatization. Mortality of Gerbera and Nephrolepis mycorrhizal plantlets was reduced at week 8 compared to the noninoculated control. A peat-based substrate low in P and with good aeration improved VAM fungi spread and efficiency. Mycorrhizal substrates had a long-term benefit of increasing leaf and root dry weight of Gerbera and Nephrolepis. Mycorrhizal Gerbera plants flowered significantly faster than non-mycorrhizal plants.

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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.