The growth of twenty plant species was compared under field conditions in a methyl bromide fumigated and non-fumigated soil. The non-fumigated soil had a wild endomycorrhizal flora and contained 100 ~tg/g of available phosphorus. No phosphorus was added to the soil but both fumigated and non-fumigated plots received a basal fertilization of 100 kg/ha N-NH4NO 3 and 100 kg/ha K-KCI. Based on plant growth responses, three groups of plants were distinguishable. Plants from group I were mycorrhizal and had better growth in non-fumigated than in the fumigated soil. This group was the most important, including sixteen plant species. Stunting of plants from group I following soil fumigation was mainly attribuable to the destruction of mycorrhizae. Plants from group II (oat and wheat) grew equally well in non-fumigated and fumigated soils. For these plants which were mycorrhizal in the non-fumigated plots, the P-content of the soil was sufficient for growth and therefore no stunting was observed in the absence ofmycorrhizae. Plants from group III (cabbage and garden beet) grew better in fumigated than in non-fumigated soil. Their better growth in fumigated soil was tentatively attributed to the destruction of soil-borne pathogens. They did not form mycorrhizae in non-fumigated soil.A new method of calculating mycorrhizal dependency is proposed, and the value calculated was named relative field mycorrhizal dependency (RFMD) index. It is also proposed that the acronym RFMD receive a superscript representing in ~tg/g the quantity of available P in the soil. Carrot with its characteristic root systems had the highest RFMD 1~176 index (99.2~o), but other plants with high phosphorus requirements for normal growth had a wide range of RFMD 1~176 index values.

. 2005. Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal development. Can. J. Plant Sci. 85: 3-14. Plants require adequate P from the very early stages of growth for optimum crop production. Phosphorus supply to the crop is affected by soil P, P fertilizer management and by soil and environmental conditions influencing P phytoavailability and root growth. Phosphorus uptake in many crops is improved by associations with arbuscular mycorrhizal fungi. Cropping system and long-term input of P through fertilizers and manures can influence the amount and phytoavailability of P in the system and the development of mycorrhizal associations. Optimum yield potential requires an adequate P supply to the crop from the soil or from P additions. Where early-season P supply is low, P fertilization may improve P nutrition and crop yield potential. Alternately, under low-P conditions, encouragement of arbuscular mycorrhizal associations may enhance P uptake by crops early in the growing season, improving crop yield potential and replacing starter fertilizer P applications. Soil P supply that exceeds P requirements of the crop may preclude mycorrhizal development. To encourage arbuscular mycorrhizal association, threshold levels of soil solution P that restrict mycorrhizal development must not be exceeded. Sustainable P management practices must be applied both in conventional and in alternative biologically based agricultural systems.Key words: Microbiology, fertility, colonization Grant, C., Bittman, S., Montreal, M., Plenchette, C. et Morel, C. 2005. Le phosphore dans le sol et les engrais : incidence sur l'absorption du P par les plantes et sur le développement des mycorhizes. Can. J. Plant Sci. 85: 3-14. Les plantes ont besoin d'une quantité suffisante de P dès le début de leur croissance si l'on veut que leur culture donne un rendement optimal. Les apports de P dépendent de la concentration de cet élément dans le sol, de l'application d'engrais phosphatés et des conditions environnementales qui affectent la quantité de P disponible pour la plante et la croissance des racines. Chez maintes cultures, l'association avec des mycorhizes à arbuscules améliore l'absorption du phosphore. Les pratiques agricoles et l'apport prolongé de P résultant de l'application d'engrais et de fumier peuvent modifier la quantité de P dont les plantes disposent dans le milieu et le développement d'une symbiose avec les mycorhizes. Pour atteindre son meilleur rendement, la culture a besoin de tirer une quantité suffisante de P du sol ou des amendements. Quand la concentration de P ne suffit pas au début de la période végétative, la fertilisation facilite parfois l'assimilation de cet élément et accroît le rendement potentiel de la culture. Dans les mêmes conditions, favoriser l'association avec les mycorhizes à arbuscules peut aider la plante à mieux absorber le P au début de la saison de croissance, ce qui en accroîtra le rendement éventuel et remplacera l'épandage initial d'engrais phosphatés. Lorsqu'il contient plus de P...

Plencette, C., Clermont-Dauphin, C., Meynard, J. M. and Fortin, J. A. 2005. Managing arbuscular mycorrhizal fungi in cropping systems. Can. J. Plant Sci. 85: 31-40. Market globalization, demographic pressure, and environmental degradation have led us to reconsider many of our current agricultural systems. The heavy use of chemical inputs, including fertilizers and pesticides, has resulted in pollution, decreased biodiversity in intensively-farmed regions, degradation of fragile agro-ecosystems, and prohibitive costs for many farmers. Low input sustainable cropping systems should replace conventional agriculture, but this requires a more comprehensive understanding of the biological interactions within agro-ecosystems. Mycorrhizal fungi appear to be the most important telluric organisms to consider. Mycorrhizae, which result from a symbiosis between these fungi and plant roots, are directly involved in plant mineral nutrition, the control of plant pathogens, and drought tolerance. Most horticultural and crop plants are symbiotic with arbuscular mycorrhizal fungi. Mycorrhizal literature is abundant, showing that stimulation of plant growth can be mainly attributed to improved phosphorous nutrition. Although the mycorrhizal potential of its symbiosis to improve crop production is widely recognized, it is not implemented in agricultural systems. There is an urgent need to improve and widely apply analytical methods to evaluate characteristics such as, relative field mycorrhizal dependency, soil mycorrhizal infectivity, and mycorrhizal receptivity of soil. Decreased use of fertilizers, pesticides, and tillage will favour arbuscular mycorrhizal fungi. However, shifting from one system to a more sustainable one is not easy since all components of the cropping system are closely linked. Different cases, from actual agricultural practices in different countries, are analyzed to highlight situations in which mycorrhizae might or might not play a role in developing more sustainable agriculture. Key words:Cropping systems, mycorrhizae, sustainability, technical itineraries, rotation Plencette, C., Clermont-Dauphin, C., Meynard, J. M. et Fortin, J. A. 2005. Gestion des champignons mycorchiziens a arbuscules dans les systemes de culture. Can. J. Plant Sci. 85: 31-40. La globalisation mondiale du marché, la pression démographique et la dégradation de l'environnement ont, dans plusieurs parties du monde, mené à une réévaluation des systèmes agricoles actuels. Les modifications de l'environnement montrent que l'utilisation des engrais et des pesticides a atteint ses limites : pollution et perte de biodiversité dans les régions d'agriculture intensive, dégradation des systèmes agricoles les plus fragiles, coûts prohibitifs pour les producteurs les plus pauvres. L'agriculture conventionnelle doit s'orienter vers des pratiques plus durables, mais les systèmes de culture durable à faibles intrants ne pourront être viables que par une meilleure connaissance et maîtrise des interactions biologiques dans ces agro-systèmes. Les champign...

A greenhouse experiment was carried out comparing the growth of various plant species in non-fumigated, fumigated, and fumigated-inoculated soils. The soil used contained numerous pieces of root of Broom-Corn Millet (Panicum miliaceum L.) that were found intensely colonized by indigenous endomycorrhizal fungi. The soil was fumigated with methyl bromide and the inoculum used was a mixture of VA mycorrhizal root fragment from plants grown in the field from which the soil was collected. Plants used were cabbage (Brassica oleracea L. var Copenhagen Market), carrot (Daucus earota L. var. Nantaise), leek (Allium porrum L. var. American Flag), marigold (Tagetes patulus L. vat. Golden Boy), tomato (Lycopersicum esculentum Mill. var. Michigan Ohio), sweet corn (Zea mays L. var. Span Cross) and wheat (Triticum aestivum L. var. Glenlea). No phosphorus was added to the soil which contained 93 ~tg/g of available P (bray II). All plants tested formed mycorrhizae except cabbage. Generally, values of the root endomycorrhizal colonization (REC) index were higher in fumigated-inoculated soil than in non-fumigated soil. Cabbage grew equally well in fumigated and fumigated-inoculated soil, but better than in non-fumigated soil. Cabbage did not form VA mycorrhizae and its better growth in fumigated soil was tentatively attributed to the destruction of soil-borne pathogens and the absence of competition. Wheat grew equally well in the three treatments, because 93 I~g/g of available P is sufficient for wheat growth and thus the mycorrhizae were not efficient. The five other plant species used were severely stunted in fumigated soil and the inoculation permitted the reestablishment of normal growth as in non-fumigated soil. Growth stimulation is attributed to the efficiency of VA mycorrhizae since these plants were mycorrhizal in non-fumigated soil and in fumigated-inoculated soil. Stunting of these plants in fumigated soil was due to the destruction of VA mycorrhizae since results show that this stunting cannot be attributed to methylbromide residues in the soil. Moreover soil pH and nutrient content were not markedly changed after fumigation. * To be submitted by C. Plenchette in partial fulfillment for the Ph.D. degree at Laval University. Soil Research Service contribution # 315. M.A.P.A.Q.

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The aims of this study were to test the effects of a mycorrhiza helper bacterium (MHB), Pseudomonas monteilii strain HR13 on the mycorrhization of (1) an Australian Acacia, A. holosericea, by several ectomycorrhizal fungi or one endomycorrhizal fungus Glomus intraradices, and (2) several Australian Acacia species by Pisolithus alba strain IR100 under glasshouse conditions. Bacterial inoculant HR13 significantly promoted ectomycorrhizal colonization for all the Acacia species, from 45.8% ( A. mangium) to 70.3% ( A. auriculiformis). A stimulating effect of HR13 on the ectomycorrhizal establishment was recorded with all the fungal isolates (strains of Pisolithus and Scleroderma). The same effect of bacteria on the frequency of endomycorrhizal colonization of A. holosericea seedlings by G. intraradices with vesicles and hyphae frequencies was recorded. The stimulation of saprophytic fungal growth by MHB is usually the main mechanism that could explain this bacterial effect on mycorrhizal establishment. MHB could stimulate the production of phenolic compounds such as hypaphorine and increase the aggressiveness of the fungal symbiont. However, no significant effect of MHB on fungal growth was recorded with Scleroderma isolates under axenic conditions but positive bacterial effects were observed with Pisolithus strains. From a practical viewpoint, it appears that MHB could stimulate the mycorrhizal colonization of Australian Acacia species with ectomycorrhizal or endomycorrhizal fungi, and could also facilitate controlled mycorrhization in nursery practices where Acacia species are grown for forestation purposes.

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Seven banana cultivars (Musa acuminata, AAA group) were inoculated with two species of vesicular arbuscular mycorrhizal (VAM) fungi (Glomus mosseae and Glomus macrocarpum) in a greenhouse experiment. Inoculated plants had generally greater shoot dry weight and shoot phosphorus concentrations compared to the noninoculated plants. A great variation in dependency on mycorrhizal colonization was observed among the banana cultivars. Cv. Williams showed the highest relative mycorrhizal dependency (RMD) and cv. Poyo the lowest. For all the cultivars studied, inoculation with G. macrocarpum resulted in the highest RMD values. Both root dry weight and root hair length or density of the noninoculated plants were inverserly correlated with the RMD values of cultivars.