The potential impact of propane flamers on the development and release of ascosporic inoculum of Venturia inaequalis (Cke.) Wint. from infected dead apple (Malus domestica Borkh.) leaves that overwintered on the soil of an experimental orchard was assessed. Thermal reduction of scab primary inoculum was first conducted under controlled conditions using an indoor testing facility. At the time of ascospore maturation, heavily infected leaves were submitted to temperature rises ranging from 150 to 200 °C with open-flame burners, thus reducing the number of ascospores subsequently released by 76% and 87%, respectively. During Spring 1995, thermal treatments of overwintered dead leaves were performed directly on the ground of an apple orchard with an experimental propane flamer design to generate uniform heat at ground level. Four thermal treatment strategies, involving two dates of flaming and two heat intensities, were tested. Flaming orchard ground, when performed in early May, before significant development of ground cover, reduced the number of ascopores released from infected dead leaves by half. A significant residual effect of the treatments on ascospore ejection was still observed 2 and 4 weeks after the treatments, thus indicating that ascospore maturation inside the leaves may be reduced by heat treatment. These results indicate potential for propane flamers to reduce apple scab primary inoculum in orchards.
H. Desilets, S. Rochefort, J. Coulombe, S. Yelle, and J. Brodeur
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.
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.