Arbuscular Mycorrhizal Fungi Strains Research Articles

Improvement of cowpea productivity by rhizobial and mycorrhizal inoculation in Burkina Faso

Cowpea is one of the most important food legume crops in Burkina Faso. It is able to associate with arbuscular mycorrhizal fungi (AMF) and rhizobia. This dual symbiosis improves nitrogen and phosphorus nutrient uptake in cowpea. As the application of exotic inoculants frequently lacks positive responses in field experiments, this study set out to select well-adapted native symbiotic rhizobial and AMF strains. Soil samples were collected from six study sites in three different climatic zones of Burkina Faso to investigate their native symbiotic strains. Soil-extraction of native spores led to the identification of four AMF genera (Scutellospora, Gigaspora, Glomus and Entrophospora) by morpho-anatomical characterization. The two most effective cowpea fungal strains were selected after spore isolation from field-collected soils, multiplication on maize roots and inoculation on cowpea seedlings in a greenhouse experiment. Cowpea-nodulating rhizobial strains were trapped in the greenhouse by planting cowpea seeds in collected soil samples and the strains were characterized using molecular methods. This characterization led to the rhizobial isolates being classified in four clusters on the phylogenetic tree (using the Maximum-Likelihood Phylogenies method). All strains belonged to the Bradyrhizobium genus and most of them were included in the B. japonicum branch. Some groups were clearly distinct species already identified and may be new species. The two most effective strains for cowpea yield improvement in the field were selected after cowpea inoculation in a greenhouse experiment. The inoculation design in the field experiment consisted of four single inoculation treatments, either rhizobial or mycorrhizal, along with four dual inoculations, one treatment with chemical fertilizers, and one uninoculated control. The results showed that cowpea productivity was significatively improved by dual inoculation with native rhizobial and mycorrhizal strains, reaching the same level as the application of commonly used chemical fertilizers [Nitrogen, Phosphorus and Potassium fertilizers (NPK)]. In addition, dual inoculation resulted in the highest iron content in cowpea leaves.

The differential and interactive effects of arbuscular mycorrhizal fungus and phosphorus on the lateral root formation in Poncirus trifoliata (L.)

Both arbuscular mycorrhizal fungi (AMF) and phosphorus (P) can regulate the lateral root (LR) formation of plants; however, the differences in their regulation and whether auxin is involved in the regulation are less understood, especially for woody plants. In this study, trifoliate orange (Poncirus trifoliata (L.) Raf) plants were inoculated with AMF strain, Rhizophagus irregularis BGC JX04B, under two P levels in pot culture. The influences of AMF and P level on LR formation were investigated, and the expression of LR- and auxin-related genes were quantified. Results showed that the mycorrhizal colonization at low P level was higher than that at high P level. AMF increased shoot biomass and decreased R/S ratio. The numbers of 1st and 2nd LR were significantly increased by AMF, while high P level only increased 2nd LR number. Variation partitioning analysis indicates that AMF was more effective than P level in regulating LR formation. At 2 MAT (month after transplanting), AMF significantly increased the expression of PSK6 and RSI-1, and high P level significantly increased the expression of KRP6. At 4 MAT, AMF significantly increased the expression of PSK6, but decreased the expression of KRP6. High P level significantly inhibited the expression of NAC1, while AMF increased the expression of NAC1 at low P level at 2 MAT, promoting the LR formation. AMF also significantly increased the expression of NAC1 at 4 MAT. Besides, the development of 1st and 2nd LR presented a positively significantly relation with the expression of PSK6 and NAC1, and 2nd LR also with the expression of TIR1. Taken together, these data suggest that AMF and P level differentially affect the LR formation in P. trifoliata via auxin signaling.

Field Trials Reveal Ecotype-Specific Responses to Mycorrhizal Inoculation in Rice.

The overuse of agricultural chemicals such as fertilizer and pesticides aimed at increasing crop yield results in environmental damage, particularly in the Sahelian zone where soils are fragile. Crop inoculation with beneficial soil microbes appears as a good alternative for reducing agricultural chemical needs, especially for small farmers. This, however, requires selecting optimal combinations of crop varieties and beneficial microbes tested in field conditions. In this study, we investigated the response of rice plants to inoculation with arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) under screenhouse and field conditions in two consecutive seasons in Senegal. Evaluation of single and mixed inoculations with AMF and PGPB was conducted on rice (Oryza sativa) variety Sahel 202, on sterile soil under screenhouse conditions. We observed that inoculated plants, especially plants treated with AMF, grew taller, matured earlier and had higher grain yield than the non-inoculated plants. Mixed inoculation trials with two AMF strains were then conducted under irrigated field conditions with four O. sativa varieties, two O. glaberrima varieties and two interspecific NERICA varieties, belonging to 3 ecotypes (upland, irrigated, and rainfed lowland). We observed that the upland varieties had the best responses to inoculation, especially with regards to grain yield, harvest index and spikelet fertility. These results show the potential of using AMF to improve rice production with less chemical fertilizers and present new opportunities for the genetic improvement in rice to transfer the ability of forming beneficial rice-microbe associations into high yielding varieties in order to increase further rice yield potentials.

Mycorrhiza consortia suppress the fusarium root rot (Fusarium solani f. sp. Phaseoli) in common bean (Phaseolus vulgaris L.)

The ability of Arbuscular Mycorrhizal Fungi (AMF) to alleviate the lethal effects incited by root pathogens in a range of plant hosts has been demonstrated. Accumulated evidence also shows that multiple rather than single AMF species exhibit greater potential against pathogens and could mimic natural systems. Nevertheless, it is well established that the effectiveness of a consortium of beneficial organisms is function of interaction among the partners and the involved host. In the present study, four AMF formulations made up of three strains each (1:1:1 w/w) from propagated units of selected AMF strains, Glomus intraradices, Glomus hoi, Gigaspora margarita, and Scutellospora gigantea were evaluated in enhancing common bean (Phaseolus vulgaris L.) growth and biocontrol vis-à-vis Fusariumsolani under greenhouse conditions. The results revealed that all the mycorrhizal preparations significantly reduced the levels of disease severity and incidence in infected bean plants. The biocontrol efficiency of AMF was a function of genera diversity. Though, either neutral or significantly increased growth parameters were recorded upon mycorrhizal colonization. The rhyzospheric competence (root colonization and spore density) of the mycorrhizal formulations was negatively affected upon Fusarium solani inoculation. Moreover, the total soluble phenols and flavonoids contents as well as the specific activity of Phenylalanine Ammonia Lyase (PAL) were boosted after mycorrhizal colonization, indicating the strengthening of plant immune system against the pathogen. Further studies should confirm our formulations after open field assays as alternatives to agrochemicals.

Biological control of strawberry crown rot is substrate dependent phenomenon

BACKGROUND: Phytophthora cactorum crown rot is currently limiting strawberry cultivation worldwide. Arbuscular mycorrhizal fungi (AMF) and bacterial endophytes have shown promising results as biological control against the disease. Growing medium can also influence biological control and e.g., composts have been shown to suppress soil borne pathogens. OBJECTIVE: The aim of the study was to investigate the effect of AMF, endophytic bacteria and different growing media against strawberry crown rot. METHODS: Three pot experiments were conducted in greenhouse conditions. Each experiment tested different biological control methods with micropropagated strawberry ‘Jonsok’ inoculated or not with the fungus. The first experiment evaluated AMF strains on different growing media, the second experiment tested combinations of AMF and other biocontrol microbes. The third experiment tested the impacts of AMF, Pseudomonas fluorescens and compost. RESULTS:Biological control methods and disease inoculation had very different impacts on strawberries planted in different growing media. On suitable growing media, AMF increased growth and lowered disease symptoms, but P. fluorescens was not effective. The growing medium containing manure/wood fiber compost was the most disease suppressive. CONCLUSIONS: Biological control of strawberry crown rot with AMF is substrate dependent. Composts can be used to somewhat suppress crown rot.

Effect of NPK Fertilizers and Co-inoculation with Phosphate-Solubilizing Arbuscular Mycorrhizal Fungus and Potassium-Mobilizing Bacteria on Growth, Yield, Nutrient Acquisition, and Quality of Tobacco (Nicotiana tabacum L.)

ABSTRACTIn the present study, the effects of inoculation of biofertilizers (phosphorus-solubilizing arbuscular mycorrhizal (AM) fungi (AMF), Glomus intraradices, and potassium-mobilizing bacterium (KMB), Frateuria aurantia) in combination with chemical fertilizers nitrogen, phosphorus, and potassium (NPK) on growth, yield, nutrient acquisition, and quality of tobacco were observed in pot culture. Factorial combinations of biofertilizers (AMF and KMB) and chemical fertilizer (NPK) alone and in combination were applied to see the effects on growth, biomass, nutrient acquisition, and leaf quality in tobacco. Results showed that bioinocula applied either singly or in combination did not significantly enhance soil availability of P and K, indicating their unsuitability for direct application. Application of chemical fertilizer in combination with both AMF and KMB strains consistently increased availability of P and K in the soil, improved leaf quality parameters, and enhanced plant growth and vigor, suggesting the potential use of AMF and KMB as biofertilizers in sustainable tobacco crop production.

Flavonol Glucoside and Antioxidant Enzyme Biosynthesis Affected by Mycorrhizal Fungi in Various Cultivars of Onion (Allium cepa L.).

The objective of this study was to investigate the impact of mycorrhizal symbiosis on qualitative characteristics of onion (Allium cepa L.). For this reason, five onion cultivars with different scale color and three different strains of arbuscular mycorrhizal fungi (Diversispora versiformis, Rhizophagus intraradices, Funneliformis mosseae) were used. Red cultivars, mainly 'Red Azar-shahr', showed the highest content in vitamin C, flavonols, and antioxidant enzymes. Mycorrhizal inoculation increased total phenolic, pyruvic acid, and vitamin C of onion plants. Considerable increase was observed in quercetin-4'-O-monoglucoside and isorhamnetin-4'-O-monoglucoside content in plants inoculated with Diversispora versiformis, but quercetin-3,4'-O-diglucoside was not significantly influenced. Analyses for phenylalanine ammonia-lyase (PAL) and antioxiodant enzyme activities such as polyphenol oxidase (PPO), catalase (CAT), and peroxidase (POD) revealed that all except PPO were enhanced by mycorrhizal inoculation. Overall, these findings suggested that mycorrhizal inoculation influenced biosynthesis of flavonol glucosides and antioxidant enzymes by increasing nutrient uptake or by induction of the plant defense system.

Efficacy of AM Fungal strains in Maize under Sterilized Pot Condition

Inoculation with strains of arbuscular mycorrhizal fungi increased dry weight of maize root and shoot from 84.8 to 187.1% and 56.3 to 145.8% respectively over the uninoculated control. The plant height, per cent root colonization, population of AM fungal spores and mycorrhizal dependency of maize at 60 days after sowing (DAS) as influenced by different AM strains ranged from 47.26 to 87.33, cm plant−1, 63.66 to 92.66%, 439.66 to 583.00 spores 100 g−1 soil and 161.73 to 277.13% per cent in maize, respectively. Phenotypic and genotypic variations in response to AMF colonization is found between plant culti-vars, genotypes, ecotypes, with respect to nutri-ent acquisition and growth. In general Glomus ACP-1 strain caused maximum value of all the parameters. The maximum shoot fresh & dry weight, root dry weight, spore population, root colonization, mycorrhizal dependency in maize crop was observed due to Glomus ACP-1 strain which was statistically at par with Glomus ACP-2.

Contribution of inoculation with arbuscular mycorrhizal fungi to the bioremediation of a copper polluted soil using Oenothera picensis

The Bradford-reactive soil protein (BRSP) fraction includes glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi that is able to bind some metals, such as copper (Cu), which could promote the bioremediation of Cu-polluted soils. This study aimed to analyze the Cu-binding capacity of BRSP in Oenothera picensis that was inoculated or not inoculated with AM fungi. O. picensis plants were established in a Cu contaminated sterilized soil and treated with the following: i) uninoculated (-M); ii) inoculated with native AM fungal propagules (+M); or iii) inoculated with a Claroideoglomus claroideum (CC) strain isolated from non-contaminated soil. In each case, five Cu levels were applied to the soil (basal level 497.3 mg Cu kg-1): 0 (T1); 75 (T2); 150 (T3); 225 (T4); and 300 mg Cu kg-1 (T5). A high BRSP accumulation in AM inoculated treatments, especially with CC, was observed. A higher Cu-bound-to-BRSP content was found with increasing Cu concentrations, representing up to 20-22% of the total Cu in the soil. Moreover, a higher root Cu concentration in +M was observed. These results suggest a high Cu binding capacity by BRSP, which is a relevant aspect to consider in the design of bioremediation programs together with the selection of endemic metallophytes and AM fungal strains, which are able to produce glomalin at high quantities.

Limited impact of arbuscular mycorrhizal fungi on clones of Agrostis capillaris with different heavy metal tolerance

The present study addresses the question whether heavy metal (HM) tolerance of host plants determines how arbuscular mycorrhizal (AM) symbiosis affects their response to increasing HM stress. Two clones of the pseudometallophyte Agrostis capillaris, one originating from a HM-contaminated site (PH) and one from an uncontaminated site (NC), were grown along a gradient of polymetallic contamination and either inoculated or not with an HM-tolerant AM fungal strain of Rhizophagus irregularis.Plant growth and chlorophyll concentrations decreased with rising substrate contamination much more in the NC clone. This HM-sensitive clone also accumulated significantly more Pb, Cd, Zn and Cu in its shoots when grown in the contaminated substrates. Contrary to our hypothesis, these marked inter-clonal differences little affected the outcome of the interaction of A. capillaris with AM fungi along the contamination gradient. Inoculated plants showed generally higher chlorophyll concentrations and a lower carotenoids/chlorophyll ratio. The rise in the chlorophyll a/b ratio due to the AM inoculation in the most contaminated substrate indicated a role of AM fungi in the alleviation of intense HM-induced oxidative stress. The AM inoculation also increased plant P concentrations, especially in the roots, but this influence diminished with rising contamination. These promotional effects of the AM inoculation were, however, not reflected in plant growth, and inoculated plants showed unchanged or even reduced shoot dry weight. The impact of AM fungi on HM uptake and root-to-shoot translocation depended on the contamination level, clone and particular metal, without any significant effect recorded in the contaminated substrates for Pb, which was the main contaminant. In spite of evidencing certain positive effects of AM fungi on the physiological state of their hosts, our data provide little support for AM inoculation as an economically feasible strategy for A. capillaris-based revegetation of HM-contaminated sites.

Arbuscular mycorrhizal symbiosis enhanced growth and antioxidant metabolism in date palm subjected to long-term drought

Arbuscular mycorrhizal symbiosis can help date palm to cope with the oxidative stress induced by long-term drought due to its capacity to enhance host plant antioxidant defense system. Plant adaptation to water scarcity is mostly the result of existing intrinsic traits. However, mycorrhizal symbiosis is widely believed to provide complementary characteristics that improve host plants protection against the deleterious effect of drought. We previously showed that arbuscular mycorrhizal (AM) date palm seedlings suffered less water stress imposed by short period of water deficiency due to a primary drought avoidance effect by the AM symbiosis related to difference in water and nutrients status between mycorrhizal and non-mycorrhizal plants. The objective of this investigation was to study the impact of long-term drought stress (LTDS, 25 % field capacity) on changes of antioxidant metabolism in non-mycorrhizal and mycorrhizal (colonized with Rhizophagus intraradices or Funneliformis mosseae) date palm seedlings. Obtained results revealed that LTDS induced clear decreases in shoot height (SH), root length (RL) and shoot (SDW) and root (RDW) dry weights. However, AM colonization alleviated the detrimental effect of LTDS on growth performance of date palm seedlings. Moreover, AM colonization mitigated drought-induced oxidative stress by alleviating H2O2 and malondialdehyde (MDA) accumulation and enhancing antioxidant enzymes activities, e.g., catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (G-POD). Our results revealed different responses of mycorrhizal seedlings to LTDS depending on AM fungi strains. R. intraradices (Ri) induced the highest SH and RL, the highest SDW and RDW and the highest mycorrhizal dependency. Ri-plants exhibited the lowest MDA and H2O2 contents and the highest CAT, SOD, APX and G-POD activities. Furthermore, Ri-plants showed the lowest oxidative damage and the highest proteins and soluble sugars contents. Thus, AM colonization enhanced date palm strategies involving antioxidant defense system to cope with the LTDS-induced oxidative stress.

Role of arbuscular mycorrhizal fungi on the performance of floodplain Phragmites japonica under nutrient stress condition

A pot experiment was conducted to evaluate the potential effects of arbuscular mycorrhizal fungi (AMF) on growth, nutrient uptake, and inoculation effectiveness on Phragmites japonica. Spores of AMF strains (Gigaspora margarita Becker & Hall) were collected from the commercial product ‘Serakinkon’. Four treatments, namely, natural soil (NS), natural soil inoculated by AM fungi, sterilised soil (SS) inoculated by AM fungi, and SS without AM fungi inoculation were selected to determine the effects of applied and indigenous AMF on P. japonica. The average colonisation level of P. japonica was 24–33%, whereas no colonisation was found in the SS. AMF colonisation increased the chlorophyll content (r = 0.84, p < .01), plant dry mass (r = 0.89, p < .01), and N, P, K, Mg, and Fe concentration of the plant's roots, stems, and leaves when AMF was applied with natural and SS. In all cases, maximum values were found when the plants were applied with NS in combination with AMF, but Ca concentration decreased as the colonisation level increased. Mn concentration decreased in the roots, but increased in the leaves. Cu concentration was not significantly affected by treatments. N-loss minimisation from the soil was significant when the colonisation level was high.

Potentialities of ecological engineering strategy based on native arbuscular mycorrhizal community for improving afforestation programs with carob trees in degraded environments

Efficient afforestation programs are crucial to limit soil degradation in various arid and semi-arid ecosystems. However, the success of these programs is dependant to the plant type selected for revegetation and the methods used for seedling production. Exotic fast-growing trees have been largely planted but their use is currently controversial because of their potential negative ecological impacts. Whereas the positive impact of arbuscular mycorrhizal (AM) fungal inoculation in nursery was demonstrated, few studies focused on the monitoring of mycorrhizal inoculation in arid and semi-arid ecosystems. In addition, the majority of studies are based on single-species inocula with non native AM fungal strains. The current study aims at evaluating the efficiency of mycorrhizal inoculation of the emblematic Mediterranean carob tree (Ceratonia siliqua) in a Moroccan degraded site, through an ecological engineering strategy based on the use of a complex native AM community (naturally associated to carob trees). Results demonstrate the high potential of this approach by improving sustainably the growth and nutrient status of carob trees in a 3-year-old plantation and also by inducing a positive soil microbial environment for nutrient cycling and environmental stress resistance.

Arbuscular mycorrhizal influences on growth, nutrient uptake, and use efficiency of Miscanthus sacchariflorus growing on nutrient-deficient river bank soil

The potential effects of arbuscular mycorrhizal fungi (AMF) on growth, nutrient assimilation, and inoculation effectiveness of AMF on the pioneer plant Miscanthus sacchariflorus which is dominant in river banks were evaluated. A pot experiment was performed in a greenhouse at Saitama University, Japan. Spores of AMF strains were collected from the commercial product ‘Serakinkon’. The average colonization level of M. sacchariflorus was 23–28%, whereas no colonization was found in sterilized soil. AMF colonization increased the chlorophyll content, plant dry mass, N, P, K, Mg, Fe, Cu, and Zn concentration of the M. sacchariflorus plant’s roots, stems, and leaves when it was applied with natural and sterilized soil. In all cases, maximum values were measured when the M. sacchariflorus plant was applied with natural soil in combination with AMF, but Ca concentration decreased as colonization level increased. Mn concentration decreased in roots and stems but increased in leaves in natural soil, and AMF with natural soil treatment. N loss minimization from the soil was significant when colonization level was high. Therefore, AMF have some potential effects for growth of the C4 grass Miscanthus sacchariflorus and nitrogen retention in aquatic–terrestrial inter-faces (river banks).

Interactive effect between Cu‐adapted arbuscular mycorrhizal fungi and biotreated agrowaste residue to improve the nutritional status of Oenothera picensis growing in Cu‐polluted soils

AbstractThe interactive effect of sugar beet (SB) agrowaste and arbuscular mycorrhizal (AM) fungi inoculation in response to increasing Cu levels was evaluated in the metallophyte Oenothera picensis. Plants were grown in a Cu‐added soil (0, 100, or 500 mg Cu kg−1), in presence or absence of SB, and inoculated with: (1) indigenous Cu adapted mycorrhiza (IM) isolated from Cu‐polluted soils; (2) Claroideoglomus claroideum (CC); or (3) maintained uninoculated (control). Sugar beet application produced an increase in shoot biomass of 2 to 7 times, improving plant nutritional status and allowing their survival at the highest Cu concentrations. Moreover, AM fungi utilization had a positive effect promoting the plant establishment; nevertheless, Cu plant concentration as well as the mycorrhizal development in terms of AM colonization, AM spore density, and glomalin production were strictly dependent of the AM fungi strains used. Remarkable differences between AM fungi strains were observed at the highest soil Cu level where only plants colonized by IM were able to survive and grow when no SB residue was added. An interactive effect between AM fungi and SB produced a higher plant growth than plants without the amendment application, improving the plant establishment and allowing their survival at highest copper concentrations, suggesting that this combination could be used as a biotechnological tool for the phytoremediation of Cu‐polluted soils.

Different mycorrhizal fungal strains determine plant community response to nitrogen and water availability

AbstractMost research on the mycorrhizal positive–negative responsiveness continuum (or “mutualism–parasitism continuum”) has focused on individual plant species growing at different levels of P availability. Here, we explore this continuum in an experimental plant community inoculated with three arbuscular mycorrhizal (AM) fungal strains (both single and mixed) growing under four resource availability scenarios. These scenarios are a factorial combination of two levels of water and N availability. Each AM fungal strain had a different origin: an arid ecosystem, a farmland, and a mine. We hypothesized that the response of the plant community to mycorrhizal inoculum would depend on the associated AM fungal strain and would be negatively related with increased nitrogen and water availability. Our results showed that mixed‐strain AM fungal inoculation had more positive effects along a wider range of water and N availability scenarios than single‐strain inoculation. In contrast, mycorrhizal growth response of plants inoculated with a single AM fungal strain shifted from positive to neutral and negative depending on resource availability. Adaptation of each strain to its local conditions might confer different properties to the mycorrhizal symbiosis. Therefore, we conclude that AM fungal origin and environmental limiting resources are crucial factors to predict plant community mycorrhizal growth response in changing ecosystems.

Effect of Different Strains of Arbuscular Mycorrhizal Fungi (AMF) on Macro and Micro Nutrient uptake in Micropropagated Chrysanthemum Plantlets

Effect of different Arbuscular Mycorrhizal Fungi (AMF) on uptake of macro and micronutri-ents by in vitro raised plantlets of chrysanthe-mum cv. Yellow Bangla has been studied. Four AMF strains namely, Acaulospora laevis, Acau-lospora scorbiculata, Glomus fasciculatum and mixed AMF strains (Nutrilink®) were used to screen the suitable AMF strain for micropropa-gated chrysanthemum plantlets. These plantlets showed maximum accumulation of N, P and Ca both in shoots and roots at 90 DAI. Maximum K and Mg accumulation was observed at 60 DAI with the same fungal strain. The predominant effect of mixed AMF (Nutrilink®) was also ob-served in uptake of Fe and Mn at 90 DAI in both shoot and root samples. However, maximum ac-cumulation of Zn was observed in shoots of Glo-mus fasciculatum inoculated plantlets. The ex-periments revealed significant increase of nutri-ent uptake in both shoot and roots in the plant-lets inoculated with mixed AMF strains (Nutrilink®) followed by Glomus fasciculatum inoculated microplants.

Effectiveness of Selected Microbial Strains on the Growth of Sweet Sorghum

Microbial inoculants are of great importance in agro-ecology and plants. However, the symbiotic effectiveness of strains may vary between species or within the same species. Aim of the study was to select experimental microbial strains of national origin, to know its impact on growth of sweet sorghum (Sorghum bicolor) in greenhouse and sterile soil. Five strains of arbuscular mycorrhizal fungi (AMF) and eight rhizobacteria (two of them mutagenized) were compared with non-inoculated plants as control. Variables measured were index of chlorophyll SPAD, plant height, stem diameter (from the middle section), fresh biomass from stem, leaf, panicle, radical, and stem sugars content (°Brix) of every two internodes. The results showed that in the majority of cases, microbial strains exceeded the values of variables compared with control plants. The highest values of chlorophyll (41.8 SPAD), stem diameter (13.5 mm) and total fresh biomass (144.3 g), were recorded with rhizobacterias BS410 (Herbaspirillum sp.), B2709 (Pseudomonas sp.) and B4M4 (Azospirillum sp.), respectively.

Mycorrhizal strains efficacy in soybean

Inoculation with strains of arbuscular mycorrhizal fungi increased weight of fresh root, fresh shoot, dry root and dry shoot of soybean from 78.9 to 133.2 %, 71.6 to 125.4 %, 55.9 to 136.0 % and 111.5 to 169.2 % over the uninoculated control, respectively. The percent increase in plant height varied from 25.4 to 87.6 over the control. The root colonization, AM fungal spore population and mycorrhizal dependency of soybean at 60 days after sowing (DAS) as influenced by different AM strains ranged from 45.0 to 65.0 % , 336.0 to 426.0 spores 100 g-1 soil 163.13 to 232.53 % per cent in maize , respectively. Phenotypic and genotypic variations in response to AMF colonization is found between plant cultivars, genotypes, ecotypes, with respect to nutrient acquisition and growth. In general Glomus ACP-1 strain caused maximum value of all the parameters. The strains Glomus ACP-1 and Glomus ACP-2 were statistically superior in increasing the root dry weight, shoot dry weight ( along with Scutellospora ACP-2 ) and spore population. As far as the efficacy of strains is concerned, the strain Glomus ACP-1 alone caused maximum and significantly higher values of plant height and root colonization over other strains. The maximum mycorrhizal dependency was also observed with the strain Glomus ACP-1, but it was statistically at par to all the other strains, except Acaulospora ACP-1 which was least effective in increasing the mycorrhizal dependency.

Evaluation of different Vietnamese soils as potential source of arbuscular mycorrhizal fungal inoculum in Capsicum frutescens

Consumption of chili peppers (Capsicum frutescens L.) represents an important aspect of the daily diet for Vietnamese population because of its high content for antioxidant compounds. To increase the economic benefits related to chili peppers cultivation and reduce negative impacts of the high input agriculture on the environment, biological alternatives to chemical fertilizers are strongly demanded. Arbuscular mycorrhizal fungi (AMF) are well-known soil microorganisms of great interest for their potential application in agriculture as ‘bio- enhancers’ of plant performance. However selection of suitable AMF strains is time-costing and the outcome of field inoculation can be affected by the weak ability to compete among the native AMF population. In the present study we proposed a “bulk” approach to identify soil hosting AMF strains suitable for the development of inocula for C. frutescens. Three different soils were tested as source of AMF inoculum in bi-compartmented pot cultures. All the inoculated treatments performed significantly better, in terms of plant growth, compared with the non- inoculated control plants. Pots inoculated with soil from tropical forest showed the best growth performances. Molecular characterization of the AMF root assemblages highlighted differences in the composition among treatments, with the “tropical forest soil” treatment characterized by the highest number of AMF taxa colonizing the roots.