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Azadeh Behrooz, Kourosh Vahdati, Farhad Rejali, Mahmoud Lotfi, Saadat Sarikhani and Charles Leslie

Drought stress is one of the main constraints limiting worldwide crop production. Arbuscular mycorrhizae (AM) and plant growth-promoting bacteria (PGPB) such as Azotobacter chroococcum and Azospirillium lipofrum have been shown to alleviate drought stress effects. Therefore, the interaction effect of AM fungi [Glomus mosseae, G. etunicatum, and a mix of these (G. mix), and PGPB bacteria (Azotobacter chroococcum + Azospirillium lipofrum)] was investigated in 1-year-old walnut seedlings (cv. Chandler) under normal and drought stress conditions. Drought stress reduced growth (plant height, root length, number of leaves, and fresh weight) and leaf nutrient content (N, P, and Zn) significantly of walnut plants. In contrast, proline, total soluble sugar, starch peroxidase enzyme activity, and total phenolic content of walnut leaves increased under this stress. Application of fungi or bacteria, and especially their simultaneous use, alleviated the negative effects of drought stress on walnut seedlings. AM fungi and PGPB increased significantly the content of some metabolites, including total phenolic content, proline level, peroxidase activity, total soluble sugar, and starch content as well as peroxidase enzyme activity. This led to an increase in walnut plant growth under the drought stress condition. Among AM fungi, G. etunicatum was more effective in reducing drought stress symptoms than either G. mosseae or the G. mix of fungi. In conclusion, use of G. etunicatum, along with PGPB, can reduce negative effects of drought stress on walnut seedlings.

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Andrès A. Estrada-Luna and Fred T. Davies Jr.

Micropropagated cactus pear plantlets (Opuntia amyclaea Tenore) cv. Reyna were colonized with a Mexican endomycorrhiza isolate, ZAC-19 (containing Glomus etunicatum and two unknown Glomus spp.) and fertilized with two phosphorous levels (0 and 11 μg P/ml) to study their effect on plant growth and nutrient uptake. After 7 months of greenhouse culture, there was 100% survival of the micropropagated cactus pear plants. Evidence of mycorrhizal colonization was observed 5 days after inoculation, with the development of internal hyphae in root cortices. At the end of the study, high colonization occurred (48% to 54%) with no differences in P treatments. Plantlets transferred to soil began to actively grow with no lag phase. However, plant growth rate was significantly affected by treatments. Absence of P supply and lack of colonization resulted in lower dry mass and surface area of prickly pear cactus plants. In contrast, the combination of supplementary P and mycorrhizal colonization significantly increased plant growth.

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Henriette Gotoèchan, Jean Coulombe, Serge Yelle and Hèlène Desilets

Two cultivars of carrot were sown in a sandy loam soil over two seasons with and without introduction of commercial inoculum of Glomus intraradices or Glomus etunicatum, which was spread with an experimental sowing machine. VAM fungi effects on the yield and the quality of carrot varied from season to season. In 1997, both of the VAM fungi enhanced the average saleable yield of the two cultivars from 66.21 t/ha to 69.85 t/ha and 80.81 t/ha, respectively, for the treatment without the introduction of VAM fungi, G. etunicatum, and G. intraradices. The slight difference (5.03%) that occured between G. intraradices and the non-inoculated treatment, although not significant, represented 20.38% of the total percentage of rejected carrots. For the last season, the amount of rejected carrots was in the same range for all the treatments (13% to 14%). Nevertheless, both of the cultivars responded differently to mycorrhization. In both of the seasons, mycorrhizal colonization was high in all plots, with an average of 70% in the treatment without inoculation and 75% in those that received G. intraradices or G. etunicatum. In our experimental conditions, reduction of phosphate fertilization to 50% of the recommanded quantity had no influence either on the mycorrhizal colonization or on the yields.

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A. Michel-Rosales, J. Farias, S. Guzman, G. Lopez and G. Valdovinos

In western Mexico, banana is traditionally multiplied by vegetative reproduction in the orchard; recently, micropropagation of this species has increased considerably. Banana has been shown to give a positive response to AM fungal inoculation. However, the selection of efficient AM fungi species, currently propagated in vitro, has not been documented. The selection of the most-effective arbuscular mycorrhizal (AM) fungi for growth enhancement of banana vitroplants is the first step toward development of an AM inoculation system. This work reports the effect of nursery inoculation of Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. monosporum, G. mosseae, and Gigaspora margarita on the banana vitroplants growth. Pots (4 kg) containing a mixture of soil and coconut fiber (1:1) sterilized with methyl bromide were used. Treatments were arranged under a fully randomized experimental design with eight replications. The plants were harvested 120 days after inoculation and plant height, number of leaves, leaf area, fresh weight of roots, mycorrhizal colonization, and intensity of infection were measured. Glomus etunicatum, G. monosporum, G. mosseae, and G. aggregatum were shown to be the most-effective endophytes. Plant height was increased, as well as the production of banana roots in response to mycorrhizal inoculation with these fungi. On the other hand, G. intraradices and G. clarum showed low levels of colonization. The data clearly show the most efficient AM fungi for future inoculation studies in nursery banana production.

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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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Cinta Calvet, Amelia Camprubi, Ana Pérez-Hernández and Paulo Emilio Lovato

produced in either in vitro or in vivo systems indicate distinct adaptations of the fungus to the growth medium. Pawlowska et al. (1999) also observed that spores of Glomus etunicatum Becker & Gerdemann from monoxenic cultures exhibited smaller

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Rumana Yeasmin, Stephen P. Bonser, Satoru Motoki and Eiji Nishihara

AMF plants ( Fig. 6 ). This is consistent with previous observations on the leaves and roots of citrus seedlings colonized by Glomus versiforme during drought ( Wu et al., 2006 ), and leaves and roots of maize plants colonized by Glomus etunicatum

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Martin Makgose Maboko, Isa Bertling and Christian Phillipus Du Plooy

inoculated with mycorrhiza by placing a teaspoon (7 g) of Mycoroot TM granules into the planting holes; then one seedling was placed into the hole. About 100 propagules, with a minimum of 10 spores per gram comprising four AMF species, Glomus etunicatum

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Dewayne L. Ingram, John M. Ruter and Chris A. Martin

stress response to supraoptimal RZT in some plants. ‘Atropurpurea’ barberry, boxwood and ‘Wheeler’ pittosporum colonized with arbuscular mycorrhizal fungi Glomus etunicatum Baker and Gerd. and G. fasciculatum Thax. sensu Gerd. showed less stress by