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Claire Woodward, Lee Hansen, Fleur Beckwith, Regina S. Redman, and Rusty J. Rodriguez

individuals. However, all plants and animals in nature are symbiotic with microorganisms and the number of microbial cells may be greater than the number of host cells. The recent description of habitat-adapted symbiosis ( Rodriguez et al., 2008 ) indicates

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Tomohiro Okada and Yoh-ichi Matsubara

most of the terrestrial plants. AMF promotes host plant growth by enhancing phosphorus uptake through symbiosis ( Marschner and Dell, 1994 ) and hence an alternative to high inputs of fertilizers and pesticides in sustainable crop production systems

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X. Fontanet, V. Estaún, A. Camprubí, and C. Calvet

Prior to the commercial use of arbuscular mycorrhiza (AM) in the nursery, the effects of commonly used pesticides on symbiosis must be evaluated. Metalaxyl and propamocarb are two fungicides added to potting substrates to prevent diseases caused by phycomycetes. Both fungicides were incorporated into the potting substrate before the inoculation and planting of the peach-almond hybrid rootstock GF677 (Prunus persica L. × Prunus dulcis Mill. D.A. Webb). The AM fungus used were Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and Glomus intraradices Schenck & Smith. Glomus intraradices was not affected by either fungicide; however, metalaxyl adversely affected root colonization by G. mosseae and decreased rhizosphere activity as measured by esterase activity. Chemical names used: N-(2-methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate) (metalaxyl); propyl 3(dimethylamino)propylcarbamate (propamocarb).

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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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Marjorie E. Ross* and Emily E. Hoover

Cultivar may cause variation in arbuscular mycorrhizal fungi (AMF) colonization levels leading to differences in shoot growth and runner formation, and in pathogen control in strawberries. However, a clear consensus has not been reached regarding the degree to which cultivar affects the formation of the symbiosis or its functioning. The study was conducted on four commercial strawberry farms in Minnesota and Wisconsin to compare, within a farm, mycorrhizal colonization and plant response among three strawberry cultivars: `Winona', `Anapolis' and `Jewel'. At each farm, two 6 × 6 meter plots of each cultivar were randomly selected. On each of three sampling dates, 4 whole plants and soil samples were collected from these plots in the 2003 field season. Roots were separated from shoots and leaves, and fresh and dry weights were taken. Leaves and soil were dried, weighed, and submitted for nutrient analysis. Soil nutrient analyses include phosphorus (Bray P), potassium, pH, buffer pH and organic matter. Leaf tissue analyses include P, K, Ca, Mg, Na, AL Fe, MN Zn, Cu, B, Pb, Ni, Cr, and Cd. Roots were collected, frozen, and prepared for scoring using methods adapted from Koske and Gemma (1989). Presence of mycorrhizal colonization is being scored using the methods of McGongle et al. (1990). Levels of mycorrhizal colonization among different strawberry cultivars will be compared. We will also use biomass measurements, to determine mycorrhizal effects on plant growth among different cultivars. Soil and leaf analysis data will be used to determine effects of AMF on plant nutrition and compare effects among cultivars.

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Robert Augé, Keunho Cho, Jean Stutz, and Heather Toler

Colonization of roots by arbuscular mycorrhizal (AM) fungi can increase host resistance to drought stress, although the effect is unpredictable. Since AM symbiosis also frequently increases host resistance to salt stress, and since drought and salt stress are often linked in drying soils, we speculated that the AM influence on plant drought response may be linked to AM influence on salt stress. We tested the hypothesis that AM-induced effects on drought responses would be more pronounced when plants of comparable size are exposed to drought in salinized soils. In two greenhouse experiments, several water relations characteristics were measured in sorghum plants colonized by Glomus intraradices, Gigaspora margarita, or a mixture of AM species during a sustained drought following exposure to salt treatments (NaCl stress, osmotic stress, or soil leaching). The presence of excess salt in soils widened the difference in drought responses between AM and non-AM plants in just two instances: days needed for plants to reach stomatal closure, and promotion of stomatal conductance. In other instances, the addition of salt tended to nullify an AM-induced change in drought response; e.g., an AM effect on the decline in leaf or soil water potential required to cause stomatal closure disappeared when soils were salinized. Our findings confirm that AM fungi can alter host response to drought but do not lend much support to the idea that AM-induced salt resistance might help explain why AM plants can be more resilient to drought stress than their non-AM counterparts.

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Abu Shamim Mohammad Nahiyan and Yoh-ichi Matsubara

enhancing phosphorus uptake through symbiosis ( Marschner and Dell, 1994 ). Previously, we found tolerance to fusarium root rot in mycorrhizal asparagus (cv. Mary Washington 500W) plants ( Matsubara et al., 2003 ); however, many points remain unclear about

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Carolyn F. Scagel, David R. Bryla, and Jungmin Lee

. 2014 Chapter 7: Salinity stress and arbuscular mycorrhizal symbiosis in plants. In: M. Miransari (ed.). Use of microbes for the alleviation of soil Stresses. Vol. 1. Springer Science and Business Media, NY Heidari, M. 2012 Effects if salinity stress on

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Kevin R. Kosola and Beth Ann A. Workmaster

correlation between layer depth and ERM colonization found in most samples ( Fig. 4 ) was likely the result of effects of litter decomposition on one or more aspects of the symbiosis; deeper layers include older, more decomposed leaf litter, with a lower C

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Heidi A. Kratsch and William R. Graves

Although many species of Alnus Miller grow in wet soils, none is as closely associated with low-oxygen, waterlogged soils as Alnus maritima (Marsh.) Muhl. ex Nutt. (seaside alder). An actinorhizal species with promise for use in horticultural landscapes, land reclamation, and sustainable systems, A. maritima associates with Frankia Brunchorst, thereby forming root nodules in which gaseous nitrogen is fixed. Our objective was to determine how root-zone moisture conditions influence the occurrence, location, and anatomy of nodules on A. maritima. Plants of Alnus maritima subsp. maritima Schrader and Graves were established in root zones with compatible Frankia and subjected to four moisture regimens (daily watered/drained, partially flooded, totally flooded, and totally flooded with argon bubbled through the flood water) for 8 weeks. Oxygen content of the root zone, number and location of nodules on root systems, and dry weight and nitrogen content of shoots were determined. Root-zone oxygen content ranged from 17.3 kPa for daily watered/drained plants to 0.9 kPa for argon-treated plants. Across all treatments, 87% of the nodules were within the upper one-third (4 cm) of the root zone. Although shoot dry weights of daily watered/drained and partially flooded plants were not different, daily watered/drained plants had more nitrogen in their leaves (2.53 vs. 2.21 mg·g-1). Nodulation occurred in all treatments, but nodules on totally flooded roots (with or without argon) were limited to a single lobe; in contrast, multilobed nodules were prevalent on partially flooded and daily watered/drained plants. Frankia infection within submerged nodule lobes was limited to one or two layers of cortical cells. Submerged nodules developed large air spaces between cortical cells, and phenolic-containing cells appeared to inhibit Frankia expansion within the nodule. These data suggest that access to root-zone oxygen is critical to the Frankia-A. maritima subsp. maritima symbiosis, and that plants of this subspecies in the drained soils of managed landscapes may benefit more than plants in native wetland habitats from nodulation and nitrogen fixation.