Glomus Etunicatum Research Articles

Glomalin-related soil protein and water relations in mycorrhizal citrus (Citrus tangerina) during soil water deficit

Glomalin-related soil protein (GRSP), a glycoprotein of arbuscular mycorrhizal fungi (AMF) secreted into soil, governs the aggregate stability, but the role of GRSP in soil and plant water is sparsely studied. The 24-week-old red tangerine (Citrus tangerina) inoculated with Glomus etunicatum and G. mosseae were subjected to a soil drying for 12 days as soil water deficit (SWD). Length of SWD significantly reduced mycorrhizal colonization, soil hyphal length, and leaf and soil water potential (Ψ), but increased total GRSP (T-GRSP), easily extractable GRSP (EE-GRSP), and proportion of water-stable aggregates (WSAs) in >0.25 mm size, irrespective of AMF source. The AMF-inoculated seedlings showed significantly higher T-GRSP, EE-GRSP, and leaf/soil Ψ than non-AMF seedlings during SWD. A significantly positive correlation was observed for mycorrhizal colonization versus leaf or soil Ψ, and hyphal length versus leaf Ψ, suggesting that root intra- and extra-radical hyphae participated in water transport. Interestingly, in GRSP fractions, only T-GRSP was significantly positively correlated with 0.25–1 and >0.25 mm WSA and negatively with leaf and soil Ψ. These results revealed a strong glue function of T-GRSP (not EE-GRSP and hyphae) to alter the proportional distribution of WSA size, thereby aiding toward prevention of soil water loss for improving soil–plant water relations.

Increased Tolerance of Citrus (<i>Citrus tangerina</i>) Seedlings to Soil Water Deficit after Mycorrhizal Inoculation: Changes in Antioxidant Enzyme Defense System

Arbuscular mycorrhizal fungi (AMF) can enhance tolerance of plants to soil water deficit, whereas morphological observations of reactive oxygen species and antioxidant enzyme system are poorly studied. The present study thereby evaluated temporal variations of the antioxidant enzyme system in citrus (Citrus tangerina) seedlings colonized by Glomus etunicatum and G. mosseae over a 12-day period of soil drying. Root colonization by G. etunicatum and G. mosseae decreased with soil drying days from 32.0 to 1.0% and 50.1 to 4.5% in 0-day to 12-day, respectively. Compared to the non-AM controls, the AMF colonized plants had significantly lower tissue (both leaves and roots) hydrogen peroxide (H2O2) and superoxide anion radical (O2•–) concentrations during soil water deficit, whereas 1.03–1.92, 1.25–1.84 and 1.18–1.69 times higher enzyme activity in superoxide dismutase, peroxidase (POD) and catalase. In situ leaf H2O2 and root POD location also showed that AM seedlings had less leaf H2O2 but higher root POD accumulation. Furthermore, significantly higher root infection and antioxidant enzymatic activities in plants colonized with G. mosseae expressed than with G. etunicatum during the soil drying. These results demonstrated that the AMs could confer greater tolerance of citrus seedlings to soil water deficit through an enhancement in their antioxidant enzyme defence system whilst an decrease level in H2O2 and O2•–.

Effect of salinity and arbuscular mycorrhizal fungi on growth and some physiological parameters of Citrus jambheri

Arbuscular mycorrhizal (AM) fungi alleviate the unfavorable effects of salinity stress on plant growth. A pot study was conducted to determine the effects of AM fungi and salt on growth and some physiological parameters of Citrus jambheri rootstock. Four levels of salinity (2, 4, 6, and 8 dS m−1 as NaCl) and three mycorrhizal treatments (Glomus etunicatum, Glomus intraradices and non-mycorrhizal (NM) control) were used. As salinity increased, all measured characteristics of plants after 4.5-month growth except Na uptake, proline content, and electrolyte leakage decreased. Shoot dry weight and K uptake were significantly higher in G. intraradices-colonized seedlings than NM controls at all salinity levels. Root dry weight and shoot P uptake were significantly higher in G. etunicatum-colonized seedlings than NM controls at all salinity levels. G. intraradices-colonized seedlings had significantly higher proline content than NM controls and G. etunicatum-colonized seedlings at salinity levels of 4, 6 and 8 dS m−1. The electrolyte leakage percentage was significantly lower in G. intraradices-colonized seedlings than NM controls at all salinity levels. The data demonstrated that mycorrhizal citrus seedlings exhibited greater tolerance to salt stress than NM seedlings and the enhanced proline content seems to be one of the mechanisms involved.

Effect of Dispersed and Proximate Inoculation Methods of Glomus etunicatum on Root Colonization of Sorghum-Sudangrass Hybrid

Information on the effective application method of arbuscular mycorrhizal fungi (AMF) inoculum is still inadequate. This work was performed to assess two AMF inoculation methods (dispersed and proximate) on root colonization of sorghum- sudangrass hybrid (Sorghum bicolor L.). In dispersed inoculation method, spores were inoculated in 2 kg pots of soil in which 5 day-old seedlings were transplanted and maintained for 50 days. In the proximate inoculation method, spores were first introduced in 500 mL pots where seeds were sown. After 10 days, the seedlings with the 500 mL soil were transferred to 2 kg pots without disturbing the contents. After 50 days of growth, root colonization and arbuscule abundance significantly increased (over 100%) in proximate method of inoculation. Moreover, sorghum-sudangrass hybrid had higher shoot growth (182.5 cm) and Glomalin related soil protein (GRSP) production in proximate method. Nutrient accumulation, particularly total nitrogen (82.61 mg plant-1), was also found to be higher in proximate method of inoculation. Our results demonstrate that the proximate method of inoculation may improve the early stage mycorrhizal symbiosis and inoculum performance in Saemangeum reclaimed soil.

CORN (ZEA MAYS L.) GROWTH AS AFFECTED BY SOIL COMPACTION AND ARBUSCULAR MYCORRHIZAL FUNGI

A two-year research work was performed under greenhouse conditions to evaluate: 1) the effects of soil compaction on corn growth, and 2) if using different species of mycorrhizal fungi under non-sterilized and sterilized conditions can alleviate the stress of soil compaction on corn growth. After sieving the field soil and sterilizing half of it using an autoclave, it was compacted in 2-kg pots. The soil was then planted with corn seeds and inoculated with different species of AM species including Glomus etunicatum, G. mosseae, and G. intraradices. While high levels of soil compaction decreased corn growth, AM inoculation significantly enhanced root and shoot growth and hence plant growth under compaction and G. etunicatum was the most efficient one. These results are important complementary to the previously little documented results regarding the effects of AM fungi on corn growth under compaction stress and are of agricultural and ecological significance.

Effects of biofertilizer with diazotrophic bacteria and mycorrhizal fungi in soil attribute, cowpea nodulation yield and nutrient uptake in field conditions

Biofertilizer made from rocks with Acidithiobacillus releases nutrients for plants and reduces the environmental impact of fertilizer on the soil. The aim of this study is to evaluate the effects of PK rock biofertilizers mixed with earthworm compound and inoculated with free living diazotrophic bacteria and arbuscular mycorrhizal fungi (AMF) on the nodulation, yield and nutrient uptake of cowpeas (Vigna unguiculata) and on the soil attributes in field conditions. In a greenhouse experiment, three rates (4.0tha−1, 6.0tha−1, and 8.0tha−1) of biofertilizer were compared with the addition of AMF (Glomus etunicatum and Gigaspora albida). A treatment with earthworm compound (20tha−1) without AMF was used as a control. In the field experiment, the treatments were as follows: three rates of biofertilizer (4.0, 6.0 and 8.0tha−1); mineral fertilizer at the recommended rate (RR) and two times RR; and earthworm compound (20tha−1). G. etunicatum was applied to all treatments. In both experiments, the seeds were inoculated with effective Bradyrhizobium strains. In the greenhouse experiment, the highest rate of biofertilizer showed the best results for all analyzed parameters. G. etunicatum produced the higher biomass yield of cowpeas but was not competitive with the indigenous AMF in the soil. In the field experiment, the highest rate of mixed biofertilizer effectively increased the grain and shoot biomass yield and increased the available P and K in soil. The mixed biofertilizer showed potential as an alternative for mineral NPK fertilization and seems to be an important factor for soil quality and long-term fertilization.

Responses of Guava Plants to Inoculation with Arbuscular Mycorrhizal Fungi in Soil Infested with Meloidogyne enterolobii.

In the Northeast of Brazil, expansion of guava crops has been impaired by Meloidogyne enterolobii that causes root galls, leaf fall and plant death. Considering the fact that arbuscular mycorrhizal Fungi (AMF) improve plant growth giving protection against damages by plant pathogens, this work was carried out to select AMF efficient to increase production of guava seedlings and their tolerance to M. enterolobii. Seedlings of guava were inoculated with 200 spores of Gigaspora albida, Glomus etunicatum or Acaulospora longula and 55 days later with 4,000 eggs of M. enterolobii. The interactions between the AMF and M. enterolobii were assessed by measuring leaf number, aerial dry biomass, CO2 evolution and arbuscular and total mycorrhizal colonization. In general, plant growth was improved by the treatments with A. longula or with G. albida. The presence of the nematode decreased arbuscular colonization and increased general enzymatic activity. Higher dehydrogenase activity occurred with the A. longula treatment and CO2 evolution was higher in the control with the nematode. More spores and higher production of glomalin-related soil proteins were observed in the treatment with G. albida. The numbers of galls, egg masses and eggs were reduced in the presence of A. longula. Inoculation with this fungus benefitted plant growth and decreased nematode reproduction.

Comparative efficacy of arbuscular mycorrhizal fungi in combination with bioformulated Paecilomyces lilacinus against Meloidogyne incognita on tomato in two Ultisols of South-eastern Nigeria

Greenhouse experiments were conducted to evaluate the efficacy of five arbuscular mycorrhizal fungi (AMF) in combination with bioformulated Paecilomyces lilacinus (PL Gold™) against Meloidogyne incognita on tomato in two Ultisols in Nigeria. Root galling and egg production were higher in Calabar than Nsukka Ultisols. P. lilacinus application did not inhibit tomato root colonisation by any of the AMF. Double application of PL Gold™ in combination with Glomus etunicatum caused a significant change in the susceptibility of the tomato cultivar with a gall index (GI) =4.00 to (GI=2.00) in Nsukka Ultisol, while a similar result was obtained with Glomus mosseae, G. deserticola and G. etunicatum in Calabar Ultisols (GI=2.33). Application of both biocontrol agents significantly (P≤0.05) enhanced growth and yield of tomato plants. The highest fresh fruit yield was obtained in Calabar soil when Gi. gigantea was combined with double application of the bionematicide while the same result was obtained with G. deserticola in Nsukka soil.

Desenvolvimento de plântulas de pessegueiro 'Okinawa' inoculadas com micorrizas arbusculares isoladas de pomares de pessegueiros e de vinhedos

O objetivo deste trabalho foi avaliar a influência das espécies de micorrizas arbusculares (MA) Glomus clarum e Glomus etunicatum isoladas de pomares de pessegueiros e de vinhedos sobre o crescimento vegetativo, conteúdo de macronutrientes e substâncias de reserva em plantas do porta-enxerto de pessegueiro cv. Okinawa. O experimento foi conduzido em telado, com delineamento experimental de blocos casualizados, em parcelas subdivididas, com 15 plantas por parcela e quatro repetições. A inoculação dos isolados de MA favoreceu a absorção de nitrogênio, fósforo e potássio, contribuindo para que as plantas inoculadas apresentassem as maiores respostas em altura, diâmetro, área foliar, biomassa fresca e seca da parte aérea, e conteúdo de reservas, superiores às plantas não inoculadas. A eficiência da simbiose foi maior com os isolados oriundos de pomares de pessegueiros, quando comparados aos isolados oriundos de vinhedos.

수지상균근균이 인삼 (Panax ginseng C. A. Mey.)의 생장에 미치는 영향

본 연구에서는 5 종의 수지상균근균을 인삼(Panax ginseng C. A. Mey.)의 묘에 처리하여 인삼의 생장에 미치는 영향을 확인하였다. 수지상균근균 5종(Glomus mosseae, Glomus intraradices, Glomus etunicatum, Acaulospora longula, Acaulospora trappei)의 접종원을 발아 후 60일이 지난 인삼묘에 접종하여 120일간 키운 후 인삼의 건조중량, 지상부의 크기 및 엽록소 형광을 측정하였다. 그 결과 수지상균근균을 접종한 인삼의 생장이 대조구에 비해 높은 경향을 나타내었으며, 접종한 수지상균근균의 균주(종)에 따라 차이를 보였다. 특히, Glomus intraradices가 다른 종에 비해 인삼의 생장에 미치는 효과가 크게 나타났으며, 엽록소형광 값은 모든 종에 대하여 유의미한 차이를 보이지 않았다. The purpose of this study was to investigate effects of inoculation of arbuscular mycorrhizal fungi (AMF) on growth of Korean ginseng (Panax ginseng C. A. Mey.) seedlings. Five species of AMF (Glomus mosseae, Glomus intraradices, Glomus etunicatum, Acaulospora longula, Acaulospora trappei) were inoculated to ginseng seedlings at 60 days after ginseng seed germination. Dry weights, heights of the plants and chlorophyll fluorescence were measured at 120 days after inoculation of AMF. Dry weights and shoot heights were increased in seedlings inoculated with AMF compared to the controls without AMF. However, chlorophyll fluorescence of seedlings with AMF showed no significant difference compared to the control.

Mycorrhizal abundance affects the expression of plant resistance traits and herbivore performance

Summary The effects of mutualistic interactions on partner phenotype and fitness can vary with many factors, including the abundance of interacting partners. Partner abundance may determine the relative costs and benefits associated with the interaction. Although arbuscular mycorrhizal fungi (AMF) can strongly influence plant phenotype and community interactions, the effects of AMF abundance on plant resistance traits and multitrophic interactions are not well understood. We tested the hypothesis that increasing AMF abundance in soil will increase mycorrhizal colonization and affect plant biomass, foliar phosphorus concentration, the expression of plant resistance and herbivore performance. We inoculated Asclepias syriaca seedlings with Glomus etunicatum, Scutellospora fulgida and a mix of the two species in 11 AMF abundance treatments. We quantified plant phosphorus (P), growth and resistance phenotype and the performance of a specialist herbivore, Danaus plexippus on plants associated with varying amounts of fungi. Increasing abundance of S. fulgida or G. etunicatum in soil increased the proportion of plant root colonized by AMF, but root colonization by a mix of the fungi was not related to inoculum density. The abundance of S. fulgida, but not G. etunicatum, increased per cent foliar P and trichome density, but decreased latex exudation. Abundance of all AMF treatments tended to decrease specific leaf mass (SLM), and the two single‐species treatments unimodally affected the expression of total foliar cardenolides. Increasing abundance of the mix of AMF species also increased above‐ground biomass, foliar P and trichome density, but had little effect on other traits. The presence of AMF, species identity and the AMF abundance all explained significant variation in the expression of plant traits, although their relative contribution varied depending on the trait examined. Mycorrhizal abundance strongly increased caterpillar growth rate, which was associated with a decline in SLM. Synthesis. Variation in mycorrhizal abundance can profoundly influence the expression of plant resistance and subsequent herbivore performance. AMF abundance may be a key, but overlooked factor in determining the outcome of mycorrhizal mutualisms.

SELEÇÃO DE FUNGOS MICORRÍZICOS ARBUSCULARES EFICIENTES PARA PROMOÇÃO DO CRESCIMENTO DA LEGUMINOSA Mimosa artemisiana HERINGER & PAULA

RESUMO: Este trabalho teve como objetivo avaliar a eficiência simbiótica de quatro espécies de fungos micorrízicos arbusculares (FMAs) em promover o crescimento e nutrição da leguminosa Mimosa artemisiana. As sementes foram inoculadas com rizóbio e Glomus clarum (Nicolson & Schenck), Glomus etunicatum (Becker & Gerdemann), Gigaspora margarita (Becker & Hall) e Scutellospora heterogama (Nicol & Gerd) Walker & Sanders e o solo foi fertilizado para atingir 5 mg/kg de P disponível. Glomus clarum foi o fungo que favoreceu o crescimento, os teores de N, P, K na parte aérea e a nodulação da Mimosa artemisiana em relação a testemunha não inoculada, e foi o FMA mais eficiente em beneficiar o crescimento da Mimosa artemisiana, sendo recomendado sua inoculação para a formação de mudas desta leguminosa. PALAVRAS-CHAVE: Gigaspora margarita, Glomus clarum, Glomus etunicatum, micorrizas, Scutellospora heterogama

DEPENDÊNCIA MICORRÍZICA DA LEGUMINOSA Mimosa artemisiana HERINGER & PAULA

RESUMO: Este trabalho teve como objetivo avaliar o grau de dependência micorrízica de Mimosa artemisiana. As sementes foram inoculadas com rizóbium e Glomus etunicatum Becker & Gerdemann em diferentes níveis de fósforo (P0 disponível (1, 5, 32, 84 e 240 mg/kg) no solo. As plantas micorrizadas apresentaram curva típica com redução de crescimento na maior dose de P em relação às não inoculadas, as quais apresentaram resposta linear ao P aplicado. As maiores respostas à inoculação de Glomus etunicatum foram observadas com P disponível entre 32 e 84 mg/kg. As plantas deixaram de responder à inoculação com P disponível estimado de 187 mg/kg. Conclui-se que a dependência micorrízica de Mimosa artemisiana é intermediária por deixar de responder aos FMAs em níveis altos de P disponível. PALAVRAS-CHAVE: fósforo, Glomus etunicatum, inoculação.

ESTABELECIMENTO DE FUNGOS MICORRÍZICOS ARBUSCULARES EM MUDAS DE Mimosa artemisiana EM DIFERENTES SUBSTRATOS

RESUMO: A inoculação de fungos micorrízicos arbusculares (FMAs) é viável em mudas. Nesta fase as plantas são fertilizadas o que pode inibir os FMAs. Este estudo teve o objetivo de avaliar o estabelecimento de duas espécies de FMAs, consideradas eficientes em promover o crescimento de leguminosas e a fixação biológica de N2 em áreas degradadas, durante a formação de mudas de Mimosa artemisiana crescendo em diferentes substratos ricos em fósforo. O trabalho foi conduzido em casa de vegetação na Embrapa Agrobiologia em bandejas com 72 células, cada uma com 100 mL de substrato constituído de composto orgânico (30%), solo argiloso (30%) e areia (40%). O experimento constou de 5 tratamentos, sendo 2 de inoculação com Glomus clarum Nicolson & Schenck e com Glomus etunicatum Becker & Gerdemann e 3 não inoculados. Os tratamentos não inoculados constaram de uma testemunha em substrato não desinfestado, (Ni – Não tratado), uma testemunha com substrato irradiado com raios gama, (Ni – Raio gama) e uma testemunha com substrato tratado com Benomyl (Ni – Benomyl). A inoculação aumentou a colonização micorrízica das raízes, e as mudas tornaram-se bem colonizadas apesar do alto nível de fósforo no substrato, o que pode garantir a sobrevivência no transplante para áreas degradadas. PALAVRAS-CHAVE: Árvore de crescimento rápido, micorrizas, nutrição de plantas.

Elicitation of tobacco alkaloid biosynthesis by disrupted spores and filtrate of germinating spores of the arbuscular mycorrhizal fungi Glomus etunicatum

Molecules released by soil microorganisms, such as arbuscular mycorrhizal fungi (AMF), trigger plant responses prior to any physical contact. Here, it is shown that disrupted spores (DS) homogenates and exudates from germinating spores (GS) of Glomus etunicatum caused marked alterations in the content of the tobacco alkaloids nicotine, anabasine, and nornicotine and the genes involved in their biosynthesis. GS and DS were applied to the base of Nicotiana tabacum seedling stems, and 3 or 10 days later, the leaves and roots were harvested for analyses. The alkaloid contents were influenced by both elicitors and varied depending on the harvest day. In general, such variations agree with the transcript levels of putrescine N-methyltransferase, oxide reductase – A622 and nicotine N-demethylase – CYP82E4. The results are discussed in light of recent insights on chemical signaling processes between plants and AMF able to trigger different elicitation responses and their possible effects on secondary metabolism in plants.

Effects of prometryn and acetochlor on arbuscular mycorrhizal fungi and symbiotic system

Prometryn and acetochlor are common herbicides widely used to control weeds in agricultural systems. The impacts of the two herbicides on spore germination, hyphal elongation, the biomass and malondialdehyde content of carrot hairy roots were investigated using a strict in vitro cultivation system associating the Ri T-DNA-transferred carrot hairy roots with Glomus etunicatum. Alternatively, root colonization, daughter spore production and the proportion of hyphae with succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities were also investigated. No significant impact on spore germination was noted in the presence of acetochlor at all three concentrations tested, while a significant decrease was observed with prometryn only at the highest concentration. Moreover, an inverse correlation was identified between herbicides concentrations and G. etunicatum root colonization and spore production as well as hyphal SDH and ALP activity, with a positive correlation identified among these four factors. Both herbicides exerted negative effects on the arbuscular mycorrhizal (AM) fungus and symbiosis at increasing concentrations, with prometryn apparently more toxic than acetochlor. Furthermore, the AM symbiotic system was shown to improve biomass, reduce malondialdehyde accumulation and ease lipid peroxidation in carrot hairy roots and decrease damage in host plants, thus enhancing plant tolerance to adverse conditions. In this study, the effect of prometryn and acetochlor on the physiology and metabolic activities of the AM fungus Glomus etunicatum were investigated. Our findings demonstrate for the first time, the impact of the two herbicides at three concentrations (0.1, 1 and 10 mg l(-1)) on transformed carrot hairy roots/AM fungus association under strict in vitro culture conditions, which may guide the application of the two herbicides in modern agriculture.

Effects of Soil Depth and Season Variation on Community Structure of Arbuscular Mycorrhizal Fungi in Greenhouse Soils Planted with Watermelon

The characteristics of arbuscular mycorrhizal fungal (AMF) community structure in various soil depths and growing seasons of watermelon (Citrullus vulgaris) grown in commercial greenhouses in Daxing of Beijing and Weifang and Laiyang of Shandong, China were investigated using both morphological identification and denaturing gradient gel electrophoresis. The sampled soils had been used for continuous greenhouse production of watermelon for 0, 5, 10, 15, or 20 years. Glomus claroideum was the dominant species in the greenhouse soils planted for 5, 10, and 15 years in Laiyang, while Glomus mosseae and Glomus etunicatum were dominant in the nearby open farmland soil. Sorenson's similarity index of AMF community composition ranged from 0.67 to 0.84 in the soils planted for 5 years, and from 0.29 to 0.33 for 20 years among the three locations. Spore abundance, species richness, and the Shannon index were highest near the soil surface (0–10 cm) and decreased with soil depth, and higher in June and October than in August and December. Canonical correspondence analysis showed that available P and the number of years that soil had been used for greenhouse production were the main factors contributing to the variance of AMF community composition. It was concluded that the community structure of AMF was mainly influenced by soil available P and planting time of watermelon as well as by soil depth and seasonal variation in the commercial greenhouse.

Influence of Arbuscular Mycorrhizal Fungi on Growth, Mineral Nutrition and Chlorogenic Acid Content of Lonicera confusa Seedlings Under Field Conditions

Lonicera confusa, a traditional Chinese medicine herb for treating cold, flu, acute fever, and so forth, is often grown artificially in acidic soils and suffers from phosphorus (P) deficiency. A five-year field experiment was carried out to study the colonization rate, growth, nutrition, and chlorogenic acid content of Lonicera confusa seedlings inoculated with arbuscular mycorrhizal (AM) fungi, Glomus etunicatum and Glomus intraradices. Before transplanting into a field, both AM-inoculated and uninoculated control plants were cultured in nursery beds. In the plants inoculated with the AM fungi, the colonization rate decreased linearly with time and a greater decrease was observed in the plants inoculated with G. intraradices than with G. etunicatum, while the AM colonization increased from 0% to 12.1% in the uninoculated control plants 5 years after transplanting. Plant height, crown diameter, number of new branches, and flower yield increased significantly by AM inoculation as compared to the uninoculated control. Phosphorus concentrations in leaves and flowers increased, and plant uptake of nutrients, e.g., nitrogen (N), P, and potassium (K), was also enhanced significantly by AM inoculation. The Lonicera confusa seedlings had a better response to inoculation of G. intraradices than G. etunicatum in both growth and chlorogenic acid content in flowers. In contrast, both plant P uptake and P concentrations in leaves and flowers were similar between two fungal inoculations. The positive responses of Lonicera confusa to AM inoculation in growth, nutrient uptake, flowering, and chlorogenic acid content in flowers suggested that AM inoculation in nursery beds could promote the plant growth and increase chlorogenic acid content in flowers of Lonicera confusa when grown on acidic and P-deficient soils.

Arbuscular mycorrhizal fungi from New Caledonian ultramafic soils improve tolerance to nickel of endemic plant species

In order to improve knowledge about the role of arbuscular mycorrhizal fungi (AMF) in the tolerance to heavy metals in ultramafic soils, the present study investigated the influence of two Glomus etunicatum isolates from New Caledonian ultramafic maquis (shrubland), on nickel tolerance of a model plant species Sorghum vulgare, and of two ultramafic endemic plant species, Alphitonia neocaledonica and Cloezia artensis. In a first step, plants were grown in a greenhouse, on sand with defined concentrations of Ni, to appreciate the effects of the two isolates on the alleviation of Ni toxicity in controlled conditions. In a second step, the influence of the AMF on A. neocaledonica and C. artensis plants grown in a New Caledonian ultramafic soil rich in extractable nickel was investigated. Ni reduced mycorrhizal colonization and sporulation of the fungal isolates, but the symbionts increased plant growth and adaptation of endemic plant species to ultramafic conditions. One of the two G. etunicatum isolates showed a stronger positive effect on plant biomass and phosphorus uptake, and a greater reduction in toxicity symptoms and Ni concentration in roots and shoots. The symbionts seemed to act as a barrier to the absorption of Ni by the plant and reduced root-to-shoot Ni translocation. Results indicate the potential of selected native AMF isolates from ultramafic areas for ecological restoration of such degraded ecosystems.

Arbuscular mycorrhiza has limited effects on yield and quality of tomatoes grown under soilless cultivation

A study was conducted investigating the possible utilization of mycorrhiza to enhance yield and quality of tomatoes grown in a soilless culture system using sawdust or coir as growing media. The experiment was carried out in temperature-controlled and non-temperature-controlled (NTC) tunnels. Fertigation was applied at three levels (100%, 75%, and 50%) of the recommended nutrient concentration. Mycoroot™, containing four arbuscular mycorrhizal species (Glomus etunicatum, Paraglomus occultum, Glomus clarum, and Glomus mosseae), was applied at seeding, as well as transplanting. Growing tomatoes under reduced nutrient supply reduced the total soluble solids in the juice of the fruits, but improved total and marketable yield, as well as the number of marketable fruits. This effect was more substantial in the temperature-controlled tunnel than in the NTC tunnel. Fruit firmness and leaf chlorophyll concentrations were significantly higher in plants grown in the temperature-controlled tunnel. Growing tomatoes in sawdust improved the leaf Mn and Ca concentration over that of tomato plants grown in coir. Mycorrhiza colonization did not have a beneficial effect on tomato yield and quality. Further studies, including different media, nutrient composition, and concentration need to be carried out to investigate the possible effect of AMF failing to improve yield, despite AMF root colonization, and to reveal the cause of the poor beneficial effect of AMF on tomato plants grown under soilless culture.