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Valtcho D. Zheljazkov and Tess Astatkie

., 2008a , 2008b ). Previous research indicated that mycorrhizae play a role in heavy metal accumulation in plant shoots ( Dueck et al., 1986 ; Khan et al., 2000 ; Wong et al., 2007 ). Reduction of mycorrhizal associations by treating the plants with

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Neo Edwin Nyakane, Moosa Mahmood Sedibe, and Elisha Markus

fertilizers and pesticides. Various studies have shown that application of mycorrhizae can improve growth and yield through improved nutrient uptake, particularly under conditions of limited water supply, low-quality irrigation water, low soil fertility, high

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Xiuling Tian and Youbin Zheng

not detect any plant pathogens (data not shown). The objective of this study was to evaluate the inhibitory potential of three compost teas (pine bark, manure, and vermicasting), Root Rescue Landscape Powder ® (a mix of mycorrhizae and other

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R.G. Linderman and E.A. Davis

Formation of arbuscular mycorrhizae (AM) has been inhibited in soilless potting mixes that usually contain some proportion of peat moss. The cause of the inhibition has been thought to be high fertilizer P content in the media that suppresses spread of the fungal symbiont in the root tissue. However, there has also been some suggestion that the peats themselves may contribute to the inhibition. That possibility was explored in this study. A sandy-loam soil, in which mycorrhizae consistently enhance plant growth under P-limiting conditions, was amended with six different peats. Onions (Allium cepa 'White Lisbon'), as an indicator host, were grown in the mixes under P-limiting conditions, and were inoculated or not with the AM fungi Glomus deserticola or Gigaspora rosea. Plant growth response to inoculation with AM fungi (AMF) varied with the type of peat and AMF isolate. Inoculated plants generally had the highest root biomass when grown in soil amended with peat. Root colonization by the two fungal symbionts was also affected differently by different peat amendments. Root colonization by Glomus deserticola and Gigaspora rosea was inhibited by at least half of the peat types. However, the types of peat inhibitory to Gigaspora rosea colonization were not the same as those inhibitory to Glomus deserticola colonization. These results indicate that different peat amendments can suppress or enhance mycorrhiza formation on onion roots and resultant growth benefit under P-limiting conditions, depending on the mycorrhizal fungus used.

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Andreas Westphal, Nicole L. Snyder, Lijuan Xing, and James J. Camberato

, weighed fresh, and rated for root-knot nematode damage. In addition to staining of plant roots at transplanting to the pots, root sections outside of the original seedling plug were excised and stained for the presence of mycorrhizae at harvest in the

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Timothy K. Broschat and Monica L. Elliott

-arbuscular mycorrhizae on phosphate fertilizer efficiency in two tropical acid soils planted with micropropagated oil palm ( Elaeis guineensis Jacq.) Biol. Fertil. Soils 9 43 48 Bovi, M.L.A. Tucci, M.L.S. Spiering, S.H. Godoy G. Jr 2000 Biomass accumulation and

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Michelle Miller, Robert Linderman, and Leslie Fuchigami

The beneficial use of vesicular–arbuscular mycorrhizae (VAM) in mineral soils is well-documented, but little is known about the effect of soilless mixes on mycorrhizal colonization of roots. Previous research indicates that mycorrhizal colonization is affected by pH, soluble salts, phosphorus levels, cation exchange capacity, percent organic matter, and some peats. No other research has been published, to our knowledge, on the role of commonly used horticultural composts and mycorrhizal establishment. This study examined four different composts for their effect on VAM establishment using onion roots as an indicator. The composts used in the study were vermicompost, spent mushroom compost, yard waste compost, and processed manure fiber. Plant growth parameters, phosphorus (P) levels and rate of desorption, and microbial populations were analyzed in relation to the percent of VAM colonization of the roots. Significant differences were found in percent VAM colonization between composts. The primary factors influencing VAM colonization were the initial levels of P in the blends and the rate and amount of P released. The experiment raised questions about the balance between mineralized P and organic P in composts and their effect on VAM fungal spore germination.

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R.G. Linderman and E.A. Davis

Formation and function of arbuscular mycorrhizae (AM) are affected by levels of fertility in soil or fertilizers applied to soilless container mixes. For AM fungi, phosphorus (P) is the main element influencing colonization of host plant roots. The question addressed in this study was whether inorganic or organic fertilizers were more compatible with the formation and function of AM. Several controlled-release inorganic (CRI) fertilizers were compared with several organic (OR) fertilizers at different rates (½× to 4× the recommended rate) to determine (1) threshold levels of tolerance by the AM fungus Glomus intraradices in relation to root colonization, and (2) growth responses of `Guardsman' bunching onion (Allium cepa) and `Orange Cupido' miniature rose (Rosa spp.) plants grown in a soilless potting mix or sandy loam soil. AM colonization in soil was greatly decreased or totally inhibited by CRI fertilizers with high P content at the 2× rate or greater, whereas colonization was decreased but never eliminated by low-P OR fertilizers at the 3× rate or greater. Shoot growth of onions was similar with or without AM inoculation when fertilized with CRI, but in general was only enhanced by OR fertilizers if inoculated with AM fungi, compared to the noninoculated controls. Shoot and root growth of onions were significantly increased by AM inoculation when OR fertilizers were used at the 1× rate. In contrast, root growth was not increased by the combination of CRI fertilizers and AM fungal inoculation. Inoculation of miniature roses grown in sandy loam amended with 25% peat and perlite and fertilized with all the CRI or OR fertilizers resulted in high AM colonization, but without much AM-induced growth increase except where OR fertilizers or CRI fertilizers with low P were used. In a soilless potting mix, growth of miniature roses was less with OR fertilizers at the rates used than CRI fertilizers, but mycorrhiza formation was greater in the former unless P was low in the latter. These results indicate that release of nutrients from organic fertilizers, as a result of microbial activity, favors AM establishment and function more than most inorganic fertilizers unless P levels of the latter are low.

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Jason Grabosky and Nina Bassuk

CU soil is a material primarily composed of clay loam soil and crushed stone designed for use under pavement to promote street tree root growth in a durable pavement section, such as sidewalks or parking lots. One concern is the low total soil fraction from which tree roots can meet nutritive demands. At issue is the long-term nutrient management of street trees once the root zone has been rendered inaccessible due to the pavement wearing surface, although in 3-year field tests, there were no differences found between a CU soil material and an agricultural field control. CU soil treatments were produced in a fractional factorial design with a patent applied for, processed humate additive, a nursery production fertilization treatment, and a mycorrhizae inoculation package of Pt and various VAM species. The mycorrhizae/fertilizer treatment was eliminated for plant availability restrictions. Bare-root seedlings of Salix nigra Marsh. were grown in treatment containers for 5 months. A Minolta SPAD-502 was used to evaluate relative chlorophyll content as an indication of leaf tissue nutrient levels. Plant growth as a function of root dry weight, shoot dry weight, and shoot: root ratio was analyzed. Soil analyses were conducted on media samples collected at the end of the study to evaluate the impact of humate admixes in nutrient availability. The fertilization treatments positively influenced leaf color, shoot weight, root weight, and shoot: root ratio. There was no impact from the mycorrhizae inoculation on leaf color or growth. There was no impact from the humate additive on leaf color or growth. There were no additive effects found in the treatment levels.

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Peter M. Shaw and Rita Hummel

The effects of vesicular-arbuscular mycorrhizae (VAM) on the growth and flowering of Geranium `Sprinter Scarlet' in three greenhouse soilless media were investigated. All media proved to be well suited for geranium growth and VAM had no significant effect on most vegetative parameters. However, VAM significantly reduced the number of days to flowering of plants grown in Mycori-Mix and Sunshine Aggregate #4 by 6.4 and 6.6 days respectively. Plants grown in Mycori-Mix with VAM flowered 99.4 days after sowing, significantly sooner than those grown in the other media with VAM. Mycorrhizal plants in Mycori-Mix and Metro Mix had a greater number of lateral branches >5 cm in length than non-mycorrhizal in the same media. Regardless of VAM treatment, plants grown in Mycori-Mix had a greater number of visible inflorescences at harvest than the other two media.