Exotic Arbuscular Mycorrhizal Fungi Research Articles

Contribution of Native and Exotic Arbuscular Mycorrhizal Fungi in Improving the Physiological and Biochemical Response of Hulless Barley (Hordeum vulgare ssp. nudum L.) to Drought

Contribution of Native and Exotic Arbuscular Mycorrhizal Fungi in Improving the Physiological and Biochemical Response of Hulless Barley (Hordeum vulgare ssp. nudum L.) to Drought

Application of Native or Exotic Arbuscular Mycorrhizal Fungi Complexes and Monospecific Isolates from Saline Semi-Arid Mediterranean Ecosystems Improved Phoenix dactylifera’s Growth and Mitigated Salt Stress Negative Effects

The date, the palm tree (Phoenix dactylifera L.) is an important component of arid and semi-arid Mediterranean ecosystems, particularly in Morocco where it plays a considerable socio-economic and ecological role. This species is largely affected by desertification, global warming, and anthropic pressure. Salinity is a very worrying problem that negatively affects the growth and the physiological and biochemical activities of the date palm. In these arid zones, the main challenge is to develop new environmentally friendly technologies that improve crop tolerance to abiotic restraints including salinity. In this sense, Arbuscular mycorrhizal fungi (AMF) have received much attention due to their capability in promoting plant growth and tolerance to abiotic and biotic stresses. It is thus fitting that the current research work was undertaken to evaluate and compare the effects of native AMF on the development of the growth and tolerance of date palm to salt stress along with testing their role as biofertilizers. To achieve this goal, two complexes and two monospecific isolates of native and non-native AMF were used to inoculate date palm seedlings under saline stress (0 g·L−1 Na Cl, 10 g·L−1, and 20 g·L−1 Na Cl). The obtained results showed that salinity drastically affected the physiological parameters and growth of date palm seedlings, whilst the application of selected AMF significantly improved growth parameters and promoted the activities of antioxidant enzymes as a protective strategy. Inoculation with non-native AMF complex and monospecific isolates showed higher responses for all analyzed parameters when compared with the native complex and isolate. It therefore becomes necessary to glamorize the fungal communities associated with date palm for their use in the inoculation of Phoenix dactylifera L. seedlings.

Dual inoculation of soybean with <i>Rhizophagus irregularis</i> and commercial <i>Bradyrhizobium japonicum</i> increases nitrogen fixation and growth in organic and conventional soils

<abstract> Soil amendment with beneficial microorganisms is gaining popularity among farmers to alleviate the decline of soil fertility and to increase food production and maintain environmental quality. However, farm management greatly influence soil microbial abundance and function, which overly affects crop growth and development. In this work, greenhouse experiments involving soybeans were conducted to evaluate the effects of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) dual inoculation on nodulation, AMF root colonization, growth and nutrient acquisition under contrasting farming systems. The experimental treatments were AMF and/or bradyrhizobia inoculation and dual inoculation on SC squire soybean variety. The exotic AMF inoculants used were <italic>Funneliformis mosseae</italic> (BEG 12) and <italic>Rhizophagus irregularis</italic> (BEG 44) while bacteria were commercial <italic>Bradyrhizobium japonicum</italic> (USDA110) and native bradyrhizobia isolates. Experiments with soil samples from organic and conventional farms were set out using a completely randomized design with three replicates. The results demonstrated that bradyrhizobia and AMF dual inoculation consistently and significantly enhanced soybean nodule dry weight (NDW), shoot dry weight (SDW) and AMF root colonization compared with individual bradyrhizobia<italic>, </italic> AMF and non-inoculated control. Moreover, organic soil significantly (p = 0.001) increased soybean SDW, NDW and AMF root colonization compared to conventional soil. Remarkably, shoot nutrients content differed in organic and conventional farming where, shoot nitrogen, phosphorus, potassium and organic carbon were higher in organic farming than the latter. Among individual inoculants, <italic>Rhizophagus irregularis</italic> out-performed <italic>Funneliformis mosseae, </italic> while commercial <italic>Bradyrhizobium japonicum</italic> showed higher performance than native bradyrhizobia. Our results demonstrated the importance of organic farming, AMF and bradyrhizobia dual inoculation in enhancing soybean growth and nutrient acquisition. However, field trials should be assessed to determine the good performance of bradyrhizobia and AMF dual inoculation in organic farming before being popularized and adopted by farmers as a sustainable agronomical management strategy to increase soil fertility and food productivity. </abstract>

Physiological and Biochemical Behaviors of Date Palm Vitroplants Treated with Microbial Consortia and Compost in Response to Salt Stress

The main challenge of the agricultural sector is to develop new ecological technologies that increase the yields and the tolerance of crops to abiotic constraints, especially in arid areas. The objective of this study was to test the potential roles of biofertilizers, namely, arbuscular mycorrhizal fungi (AMF), a native AMF consortium (AMF1) and an exotic AMF strain (AMF2); plant growth-promoting rhizobacteria (PGPR); and compost (comp), applied separately or in combination, in improving the tolerance of date palm vitroplants to salt stress. Plants were grown under non-stressed (0 mM NaCl) or stressed conditions (120 and 240 mM NaCl). Salt stress negatively affected growth and physiological parameters. However, biofertilizers used alone or in combination increased these traits in either the presence or absence of salinity. The two tripartite combinations PGPR+AMF1+Comp and PGPR+AMF2+Comp efficiently increased plant height compared to the controls, with respective enhancements of 47% and 48% under non-stressed conditions (0 mM), 44% and 43% under 120 mM NaCl and 42% and 41% under 240 mM NaCl. Moreover, under 240 mM NaCl level, the PGPR, AMF1+Comp and PGPR+AMF1+Comp treatments improved the shoot dry weight by 128%, 122% and 113% respectively compared to the stressed control plants submitted to 240 mM NaCl. The tripartite combinations PGPR+AMF1/AMF2+Comp improved salt stress tolerance of plants by increasing plant growth, accumulation of osmotic adjustment compounds and antioxidant enzyme activity compared to control plants and the other treatments.

Comparative effect of Rhizophagus irregularis strain on cassava root development and Phosphorus uptake under acidic soils conditions of Walungu territory, Eastern DR Congo.

Objective: In the highlands of South-Kivu province of DR Congo, cassava is grown on marginal land not suitable for other crops. Walungu territory for instance is dominated by acidic soils and has the highest nutrient depletion rate in the country. On such types of soil, nutrient depletion is accompanied by a decrease in the availability of phosphorus and many other nutrients. The use of Arbuscular mycorrhizal fungi (AMF) would therefore be an alternative to improve the phosphate nutrition of cassava under different soil conditions. Methodology and results: The experiment reported in the current study was conducted in pots under semi-controlled conditions. Ferrallitic soil from Walungu was used. Soil was sterilized or not and then inoculated with the AMF Rhizophagus irregularis (RI) strain. Results showed that inoculation with an exotic AMF strain (Rhizophagus iregularis) has significantly increased root abundance (number of roots) in both sterilized and unsterilized soil and root dry weight in sterilized soil only. However, in unsterilized soil, root dry weight decreased with AMF inoculation. In Walungu acidic soils, P supply could significantly influence the effect of mycorrhizal inoculation on root development and root abundance. AMF inoculation has significantly increased the shoot P concentration when P was supplied. In sterilized soil, mycorrhizal inoculation had a depressant effect on soil phosphorus concentration, especially when P was not supplied. Conclusion and application of results: Our results suggest that the introduced Rhizophagus iregularis strain increases P uptake in the rhizospheric soil, especially when phosphorus is not applied to the sterilized or unsterilized soil. The use of the Rhizophagus irregularis strain as a biofertilizer could improve phosphorus nutrition and root development in cassava. Keywords: Arbuscular mycorrhizae, Rhizophagus irregularis, P uptake, Cassava, Ferrallitic soil

EXOTIC ARBUSCULAR MYCORRHIZAL FUNGI AND NATIVE DARK SEPTATE ENDOPHYTES ON THE INITIAL GROWTH OF Paspalum millegrana GRASS

ABSTRACT Arbuscular mycorrhizal fungi (AMF) and dark septate endophytic fungi (DSE) promote increase in plant biomass, depending on the soil and climate conditions and the interactions with the host plant. The objective of this study was to evaluate the interaction of exotic arbuscular mycorrhizal fungi and native DSE fungi on the initial growth of P. millegrana. A completely randomized experimental design comprising the Paspallum millegrana cutilvar with the following treatments: control - without AMF, and three exotic AMF isolates (UFLA351 - Rhizoglomus clarum, UFLA372 - Claroideoglomus etunicatum and UFLA401 - Acaulospora morrowiae), with four replications each. P. millegrana grass was colonized by exotic AMF by R. clarum (UFLA351, 11.9%), C. etunicatum (UFLA372, 39.6%), and A. morrowiae (UFLA401, 51.2%). P. millegrana was also colonized by native DSE fungi, but these did not interfere with the colonization by exotic AMF and plant development. P. millegrana is responsive to the inoculation of UFLAs isolates of exotic AMF, which may contribute to the grass growth and survival under field conditions. The process of surface disinfestation of seeds does not eliminate endophytic microorganisms, whose presence may influence plant colonization by AMF, as well as development of the host plant.

Arbuscular mycorrhizal fungi ameliorate the chemical properties and enzyme activities of rhizosphere soil in reclaimed mining subsidence in northwestern China

In semi-arid region of northwestern China, underground mining subsidence often results in decreased vegetation coverage, impoverishment of soil fertility and water stress. In addition, the physical-chemical and biological properties of soil also change, resulting in more susceptible to degradation. In particular, subsidence causes disturbance of the symbioses of plant and microbe that can play a beneficial role in the establishment of vegetation communities in degraded ecosystems. The objective of this study was to evaluate the effects of revegetation with exotic arbuscular mycorrhizal fungi (AMF) inoculum on the chemical and biological properties of soil over time in mining subsidence areas. Soils were sampled at a depth up to 30 cm in the adjacent rhizosphere of Amorpha fruticose Linn. from five reclaimed vegetation communities in northwestern China. In August 2015, a field trial was set up with five historical revegetation experiments established in 2008 (7-year), 2011 (4-year), 2012 (3-year), 2013 (2-year) and 2014 (1-year), respectively. Each reclamation experiment included two treatments, i.e., revegetation with exotic AMF inoculum (AMF) and non-AMF inoculum (the control). Root mycorrhizal colonization, glomalin-related soil protein (GRSP), soil organic carbon (SOC), soil nutrients, and enzyme activities were also assessed. The results showed that mycorrhizal colonization of inoculated plants increased by 33.3%–163.0% compared to that of non-inoculated plants (P<0.05). Revegetation with exotic AMF inoculum also significantly improved total GRSR (T-GRSP) and easily extracted GRSP (EE-GRSP) concentrations compared to control, besides the T-GRSP in 1-year experiment and the EE-GRSP in 2-year experiment. A significant increase in SOC content was only observed in 7-year AMF reclaimed soils compared to non-AMF reclaimed soils. Soil total N (TN), Olsen phosphorus (P) and available potassium (K) were significantly higher in inoculated soil after 1–7 years of reclamation (except for individual cases), and increased with reclamation time (besides soil Olsen P). The exotic AMF inoculum markedly increased the average soil invertase, catalase, urease and alkaline phosphatase by 23.8%, 21.3%, 18.8% and 8.6%, respectively (P<0.05), compared with the control. Root mycorrhizal colonization was positively correlated with soil parameters (SOC, TN and soil available K) and soil enzyme activities (soil invertase, catalase, urease and alkaline phosphatase) in both AMF and non-AMF reclaimed soils (P<0.05), excluding available K in non-AMF reclaimed soils. T-GRSP (P<0.05) and EE-GRSP (P<0.05) were significantly correlated with the majority of edaphic factors, except for soil Olsen P. The positive correlation between root mycorrhizal colonization and available K was observed in AMF reclaimed soils, indicating that the AMF reclaimed soil with a high root mycorrhizal colonization could potentially accumulate available K in soils. Our findings concluded that revegetation with exotic AMF inoculum influenced soil nutrient availability and enzyme activities in the semi-arid ecosystem, suggesting that inoculating AMF can be an effective method to improve soil fertility and support restoration of vegetation communities under poor conditions like soil nutrient deficiency and drought.

Tracing Rhizophagus irregularis isolate IR27 in Ziziphus mauritiana roots under field conditions.

Arbuscular mycorrhizal fungi (AMF) play a major role as biofertilizer for sustainable agriculture. Nevertheless, it is still poorly documented whether inoculated AMF can successfully establish in field soils as exotic AMF and improve plant growth and productivity. Further, the fate of an exogenous inoculum is still poorly understood. Here, we pre-inoculated two cultivars (Tasset and Gola) of the fruit tree Ziziphus mauritiana (jujube) with the exotic AM fungus Rhizophagus irregularis isolate IR27 before transplantation in the field. In two experiments, tracking and quantification of R. irregularis IR27 were assessed in a 13-month-old jujube and an 18-month-old jujube in two fields located in Senegal. Our results showed that the inoculant R. irregularis IR27 was quantitatively traced and discriminated from native R. irregularis isolates in roots by using a qPCR assay targeting a fragment of the RNA polymerase II gene (RPB1), and that the inoculum represented only fractions ranging from 11 to 15% of the Rhizophagus genus in the two plantations 13 and 18months after transplantation, respectively. This study validates the use of the RPB1 gene as marker for a relative quantification of a mycorrhizal inoculant fungus isolate in the field.

Application of Mycorrhiza and Soil from a Permaculture System Improved Phosphorus Acquisition in Naranjilla.

Naranjilla (Solanum quitoense) is a perennial shrub plant mainly cultivated in Ecuador, Colombia, and Central America where it represents an important cash crop. Current cultivation practices not only cause deforestation and large-scale soil degradation but also make plants highly susceptible to pests and diseases. The use of arbuscular mycorrhizal fungi (AMF) can offer a possibility to overcome these problems. AMF can act beneficially in various ways, for example by improving plant nutrition and growth, water relations, soil structure and stability and protection against biotic and abiotic stresses. In this study, the impact of AMF inoculation on growth and nutrition parameters of naranjilla has been assessed. For inoculation three European reference AMF strains (Rhizoglomus irregulare, Claroideoglomus claroideum, and Cetraspora helvetica) and soils originating from three differently managed naranjilla plantations in Ecuador (conventional, organic, and permaculture) have been used. This allowed for a comparison of the performance of exotic AMF strains (reference strains) versus native consortia contained in the three soils used as inocula. To study fungal communities present in the three soils, trap cultures have been established using naranjilla as host plant. The community structures of AMF and other fungi inhabiting the roots of trap cultured naranjilla were assessed using next generation sequencing (NGS) methods. The growth response experiment has shown that two of the three reference AMF strains, a mixture of the three and soil from a permaculture site led to significantly better acquisition of phosphorus (up to 104%) compared to uninoculated controls. These results suggest that the use of AMF strains and local soils as inoculants represent a valid approach to improve nutrient uptake efficiency of naranjilla and consequently to reduce inputs of mineral fertilizers in the cultivation process. Improved phosphorus acquisition after inoculation with permaculture soil might have been caused by a higher abundance of AMF and the presence of Piriformospora indica as revealed by NGS. A higher frequency of AMF and enhanced root colonization rates in the trap cultures supplemented with permaculture soil highlight the importance of diverse agricultural systems for soil quality and crop production.

Inoculation of arbuscular mycorrhizal fungi with plastic mulching in rainfed wheat: A promising farming strategy

Inoculation of arbuscular mycorrhizal fungi (AMF) is an environment-friendly solution to improve field productivity and agro-ecosystem sustainability in semiarid rainfed agricultural areas. Yet, whether it can be incorporated into plastic-film mulching farming systems is an unanswered fundamental question. In 2014 and 2015, two relatively independent but closely related field trials were conducted to evaluate the inoculation effects of AMF species on grain yield, biomass accumulation, water use efficiency (WUE), soil organic carbon and economic profitability in field-grown wheat under plastic film mulching in a typical semiarid site of northwest China. Trial 1 included two treatments: traditional flat planting (CK-1) and plastic film mulching (PFM); while Trial 2 consisted of PFM treatment inoculated with three AMF species (Acaulospora laevis, Glomus monosporum, and Glomus intraradices) alone or in combination, or without inoculation as the control (CK-2). PFM resulted in significant increases in grain yield and WUE due to improved hydro-thermal balance in both growing seasons. Importantly, across all the species under PFM, the AMF inoculation increased grain yield and aboveground biomass by 46.6% and 56.5%, respectively, in wet year 2014, and 16.6% and 27.4%, respectively, in warm dry year 2015, comparing with the non-inoculation treatment. AMF symbiosis also significantly enhanced harvest index and population fitness, and higher inoculation rates generally led to greater increases in yield, biomass and WUE. We also quantitatively estimated the economic benefits among various treatments, and found that compared with CK-1, PFM significantly increased net economic income by 35.8% in 2014 and 245.0% in 2015, while AMF inoculation further promoted average net income by 72.9% in 2014 and 21.7% in 2015 compared with CK-2. Meanwhile, the output to input ratio in PFM or PFM-mulching treatment was generally boosted or remained unchanged in comparison with that of control groups over two growing seasons. Principal component analysis (PCA) demonstrated that hydrothermal balance (PFM and precipitation) acted as the major factors to determine the grouping pattern from group I into group II, and all AMF treatment clusters into group III. Critically, PFM led to small increases in soil organic carbon (SOC) content in both growing seasons, and AMF inoculation further significantly increased the SOC by 16.5% in 2014 and 1.9% in 2015. The AMF diversity in the rhizosphere was re-tested and identified, providing evidence that three exotic AMF species had been established efficiently in rhizosphere soil and become dominant species. For the first time, we found that an integrated AMF-mulching farming system improved field productivity, economic benefit and soil organic carbon, thereby providing as environment-friendly and high-yielding management solution for wheat production and ecosystem sustainability in dryland agriculture.

High effectiveness of exotic arbuscular mycorrhizal fungi is reflected in improved rhizobial symbiosis and trehalose turnover in Cajanus cajan genotypes grown under salinity stress

Abstract Arbuscular mycorrhizal fungi (AMF) improve functioning of legume-Rhizobium symbiosis under salinity. However, plant responses to mycorrhization vary depending on the plant and fungal species. The current study aimed to compare the effectiveness of a native inoculum from saline soil and two exotic isolates, Funneliformis mosseae and Rhizophagus irregularis on two Cajanus cajan (pigeonpea) genotypes (Paras, Pusa 2002) subjected to NaCl stress. Salinity depleted nodulation and nutrient status in both genotypes with higher negative effects in Paras. Although all AM fungi improved growth, R. irregularis performed better by promoting higher biomass accumulation, nodulation, N2 fixation and N, P uptake which correlated with higher AM colonization. R. irregularis inoculated plants also accumulated higher trehalose in nodules due to decreased trehalase and increased trehalose-6-P synthase, trehalose-6-phosphatase activities. The results suggest that higher stability of R. irregularis-pigeonpea symbiosis under salt stress makes it an effective ameliorator for overcoming salt stress in pigeonpea.

Subcritical soil hydrophobicity in the presence of native and exotic arbuscular mycorrhizal species at different soil salinity levels

Soil salinity and arbuscular mycorrhizal fungi (AMF) influence the soil hydrophobicity. An experiment was performed to determine the effects of soil salinity and AMF species on soil water repellency (SWR) under wheat (Triticum aestivum L.) crop. Six AMF treatments, including four exotic species (Rhizophagus irregularis, Funneliformis mosseae and Claroideoglomus claroideum, a mix of three species), one mix native AMF species treatment and an AMF-free soil in combination with four salinity levels (1, 5, 10, and 15 dS m−1) were used. The soil repellency index (RI) increased with salinity increment ranging from 2.4 to 10.5. The mix of three exotic and native AMF treatments enhanced the RI significantly compared to AMF-free soil in all salinity levels with one exception for native treatment at 1 dS m−1. Among individual AMF species, the C. claroideum treatment at 10 dS m−1 increased the RI by 67% compared to AMF-free soil. The native AMF treatment was more efficient in root colonization, glomalin production and SWR development at 10 and 15 dS m−1, compared to exotic species. In addition to the net positive effect of salinity on SWR, the AMF influences on the RI were greatly dependent on salinity levels.

Effectiveness of native and exotic arbuscular mycorrhizal fungi on nutrient uptake and ion homeostasis in salt-stressed Cajanus cajan L. (Millsp.) genotypes.

Soil salinity is an increasing problem worldwide, restricting plant growth and production. Research findings show that arbuscular mycorrhizal (AM) fungi have the potential to reduce negative effects of salinity. However, plant growth responses to AM fungi vary as a result of genetic variation in mycorrhizal colonization and plant growth responsiveness. Thus, profitable use of AM requires selection of a suitable combination of host plant and fungal partner. A greenhouse experiment was conducted to compare effectiveness of a native AM fungal inoculum sourced from saline soil and two single exotic isolates, Funneliformis mossseae and Rhizophagus irregularis (single or dual mix), on Cajanus cajan (L.) Millsp. genotypes (Paras and Pusa 2002) under salt stress (0-100mM NaCl). While salinity reduced plant biomass and disturbed ionic status in both genotypes, Pusa 2002 was more salt tolerant and ensured higher AM fungal colonization, plant biomass and nutrient content with favourable ion status under salinity. Although all AM fungi reduced negative effects of salt stress, R. irregularis (alone or in combination with F. mosseae) displayed highest efficiency under salinity, resulting in highest biomass, yield, nutrient uptake and improved membrane stability with favourable K(+)/Na(+) and Ca(2+)/Na(+) ratios in the host plant. Higher effectiveness of R. irregularis correlated with higher root colonization, indicating that the symbiosis formed by R. irregularis had more stable viability and efficiency under salt stress. These findings enhance understanding of the functional diversity of AM fungi in ameliorating plant salt stress tolerance and suggest the potential use of R. irregularis for increasing Cajanus cajan productivity in saline soils.

Use of mycorrhizal seedlings on recovery of mined dunes in northeastern Brazil

Abstract The exploitation of minerals from coastal dunes in northeastern Brazil requires subsequent revegetation for ecosystem recovery. In mined dunes areas, we have compared the growth of Guazuma ulmifolia and Tabebuia roseo-alba seedlings using substrates containing 10 or 15% of cattle manure, uninoculated or inoculated with a mixture of native arbuscular mycorrhizal fungi (AMF) or exotic AMF (Acaulospora longula). The inoculated plants had a higher percentage of colonization than those that were uninoculated. Plants of G. ulmifolia had the highest growth when inoculated with native AMF and fertilized with 10% manure or inoculated with A. longula and fertilized with 15% manure. In general, fertilization with 15% manure did not produce greater seedling development and had a negative effect on the effectiveness of the symbiosis. Twenty one AMF species were recorded in the planting areas at the end of the experiments, with a predominance of species that form acaulosporoid spores in areas with T. roseo-alba and gigasporoid spores in areas with G. ulmifolia plants. The incorporation of 10% cattle manure and native AMF in the substrate of T. roseo-alba and G. ulmifolia seedlings contributes to the initial establishment of plants in the field and to the incorporation of AMF propagules in the soil of the revegetated mined dunes.

Different arbuscular mycorrhizae and competition with an exotic grass affect the growth of Podocarpus cunninghamii Colenso cuttings

There is growing interest in the use of arbuscular mycorrhizal fungi (AMF) for ecological restoration. Numerous commercial AMF products are now available and are often used in preference to collecting indigenous AMF in treating restoration plants. Commercial AMF products are typically based on AMF strains exotic to the plant species and locations where they are used. We treated rooted cuttings of an endemic New Zealand tree species (Podocarpus cunninghamii) and an exotic and invasive grass (Agrostis capillaris) with an indigenous, pot-cultured AMF (Acaulospora laevis) and an exotic commercial AMF product (Glomus spp.). P. cunninghamii was grown in monoculture and together with A. capillaris, the latter to simulate field competition that often occurs in restoration plantings. In monoculture, the indigenous AMF resulted in significant increases in P. cunninghamii growth rates and tissue concentrations of both nitrogen and phosphorus. The commercial AMF had either no effect or a negative effect on P. cunninghamii growth and nutrient levels. A. capillaris growth and nutrient status were unaffected by the different AMF treatments. Competition eliminated any AMF benefit for P. cunninghamii. The results show that, for our chosen indigenous woody plant species, the commercially available AMF did not improve its early growth and nutrient acquisition in monoculture while, over the same period, the indigenous AMF induced positive growth and nutrient responses. These results have potential implications for forest restoration, particularly for nursery production of indigenous woody species.

The effects of arbuscular mycorrhizal (AM) fungal and garlic mustard introductions on native AM fungal diversity

Introduced, non-native organisms are of global concern, because biological invasions can negatively affect local communities. Arbuscular mycorrhizal (AM) fungal communities have not been well studied in this context. AM fungi are abundant in most soils, forming symbiotic root-associations with many plant species. Commercial AM fungal inocula are increasingly spread worldwide, because of potentially beneficial effects on plant growth. In contrast, some invasive plant species, such as the non-mycorrhizal Alliaria petiolata, can negatively influence AM fungi. In a greenhouse study we examined changes in the structure of a local Canadian AM fungal community in response to inoculation by foreign AM fungi and the manipulated presence/absence of A. petiolata. We expected A. petiolata to have a stronger effect on the local AM fungal community than the addition of foreign AM fungal isolates. Molecular analyses indicated that inoculated foreign AM fungi successfully established and decreased molecular diversity of the local AM fungal community in host roots. A. petiolata did not affect molecular diversity, but reduced AM fungal growth in the greenhouse study and in a in vitro assay. Our findings suggest that both introduced plants and exotic AM fungi can have negative impacts on local AM fungi.

Field inoculation effectiveness of native and exotic arbuscular mycorrhizal fungi in a Mediterranean agricultural soil

In sustainable agriculture, arbuscular mycorrhizal (AM) fungal inoculation in agronomical management might be very important, especially when the efficiency of native inocula is poor. Here, we assessed the effect of native and exotic selected AM fungal inocula on plant growth and nutrient uptake in a low input Trifolium alexandrinum–Zea mays crop rotation. We evaluated the effects of four exotic AM fungal isolates on T. alexandrinum physiological traits in greenhouse. Then, the field performances of T. alexandrinum inoculated with the exotic AMF, both single and mixed, were compared to those obtained with a native inoculum, using a multivariate analysis approach. Finally, we tested the residual effect of AM fungal field inoculation on maize as following crop. Multivariate analysis showed that the field AM fungal inoculation increased T. alexandrinum and Z. mays productivity and quality and that the native inoculum was as effective as, or more effective than, exotic AM fungal isolates. Moreover, the beneficial effects of AMF were persistent until the second year after inoculation. The use of native AMF, produced on farm with mycotrophic plants species, may represent a convenient alternative to commercial AM fungal inocula, and may offer economically and ecologically important advantages in sustainable or organic cropping systems.

Efficacy of indigenous arbuscular mycorrhizal fungi for promoting white yam ( Dioscorea rotundata) growth in West Africa

Tuber yields of yam ( Dioscorea spp.), a main staple food in West Africa, are steadily declining per unit area, an incidence for which decreasing soil fertility due to increasing land pressure is largely blamed. Recent studies demonstrated the association of a plethora of arbuscular mycorrhizal fungi (AMF) with yam, soil microorganisms crucial for natural soil fertility. Thus, inoculation of yam with AMF could help reverse declining yields, above all in soils with a strong loss of AMF diversity due to agricultural land use intensification. In a pot experiment, we studied the impact of indigenous and exotic AMF isolates on growth performance of micro-propagated white yam plantlets ( Dioscorea rotundata, cv.TDr89/02461). Pots were inoculated with single spore derived isolates of Glomus etunicatum, originating from tropical environments in West Africa, South America and Asia and, for comparison, also with three isolates of other AMF species from temperate Europe. In addition, isolates of nine AMF species originating from sub-Saharan West Africa and three commercial AMF were compared. Six of the 11 isolates of G. etunicatum from the tropics increased yam tuber growth compared with non-mycorrhizal controls, whereas the European AMF species tended to be less efficient but led to an increased tuber phosphorus concentration. The African isolates of G. mosseae, G. hoi, G. etunicatum, Acaulospora scrobiculata and A. spinosa generally led to increased tuber growth compared with non-mycorrhizal controls, while isolates of G. sinuosum and Kuklospora kentinensis did not. Our study indicates that inoculation of micro-propagated yam plantlets with selected indigenous AMF could potentially constitute a sustainable measure to boost yam productivity again in degraded African soils.

Influência da inoculação de fungos micorrízicos arbusculares, da acidez do solo e de fontes de fósforo no crescimento do milho

O objetivo deste estudo foi avaliar o efeito da inoculação de fungos micorrízicos arbusculares (FMA) exóticos, da acidez do solo e de fontes de fósforo no crescimento e na composição mineral de plantas de milho, Zea mays L. (Poaceae). O delineamento experimental foi em blocos ao acaso em esquema fatorial (2x2x2), correspondendo a dois níveis de V% (21 e 60%), duas fontes de P (Na2H2PO4, Ca3 (PO4)2), inoculado e não-inoculado com FMA, com cinco repetições. A inoculação proporcionou maiores concentrações de P, K e de Cu, nas folhas de milho, diminuindo os efeitos da acidez do solo em fonte solúvel de P. O solo corrigido favoreceu o crescimento radical, o aumento da concentração de Mg nas folhas, o aumento da matéria seca da parte aérea e a diminuição de Mn nas folhas. A combinação solo corrigido - P baixa solubilidade - FM autóctones demonstrou ser a mais propícia ao desenvolvimento do cultivar de milho utilizado

Colonization, ALP activity and plant growth promotion of native and exotic arbuscular mycorrhizal fungi at low pH

Soil acidity can affect arbuscular mucorrhizal fungi (AMF) in many aspects. In this study, by inoculating white clover ( Trifolium ripens L.) with AMF at two pH levels (pH 5.0 and 6.0), we investigated the influences of low pH on the colonization, alkaline phosphatase (ALP) activity and promoting effect of AMF, and also compared the different responses of native AMF community and exotic species ( Gigaspora margarita) to low pH. PCR-DGGE profiles revealed the obvious difference in native AMF community structure between low and high pH. Compared to low pH, high pH decreased the total and vesicle colonization, external hyphae length density of native AMF, but exerted no effect on those of exotic AMF. For both native and exotic AMF, high pH enhanced the proportions of arbuscule and fungal structure with ALP activity in colonized roots. Both native and exotic AMF promoted the shoot biomass, with greater increase at low pH than at high pH. Plant growth was more dependent on exotic AMF than on native AMF at both pH levels. The same trends were observed in P uptake as in biomass. Our study suggested that the increase in pH can exert inhibitory effects on AMF species native to acidic soil, including ecological (community structure), functional (ALP activity) and developmental (hyphal length, vesicle and arbuscule percentage, total colonization) aspects, but have no effect on exotic species in the present experiment.