Arbuscular Mycorrhizal Fungi Root Colonization Research Articles

Fruit quality and volatile compound composition of processing tomato as affected by fertilisation practices and arbuscular mycorrhizal fungi application

The effects of different fertilisation treatments with arbuscular mycorrhizal fungi (AMF) inoculation on AMF root colonisation, fruit yield, nutrient and total phenol contents, volatile compound composition, and sensory attributes of tomato (Solanum lycopersicum L.) were investigated. Mineral, organic, and mineral + organic fertiliser application positively affected tomato yield (35%–50%) and phosphorus concentration (24%–29%) compared with controls. AMF application had a significant impact on the total nitrogen (+9%), manganese (+12%), and hydrophilic phenol (+8%) contents in the fruit. Volatile compounds were affected by the interactive effects of fertilisation and AMF application. The response of tomato fruit sensory quality indicators was relatively modest, with only a few sensory characteristics affected to a lesser extent. Although tomato showed susceptibility to field-native AMF, particular combinations of fertilisation and AMF inoculation were more effective at improving the quality parameters of tomatoes under field conditions applied in this study.

Different sources of phosphorus fertilizers and soil amendments affected the phosphorus and cadmium content in soil, roots and seeds of maize (Zea mays L.)

Phosphorus (P) fertilizers contain cadmium (Cd) as a contaminant at levels varying from trace amounts to high levels and therefore, can be a major source of Cd to agricultural systems. This study was designed to assess the impact on application of Eppawala rock phosphate (ERP) and triple super phosphate (TSP) as P fertilizers and different soil amendments on P and Cd uptake in maize (Zea mays L.). The field trial was carried out at Field Crop Research and Development Institute at Mahailluppallama, Sri Lanka. A randomized complete block design was employed with three replicates as ERP and TSP separately applied with arbuscular mycorrhizal fungi (AMF) and three types of amendments (biochar, compost and dolomite) and the control without adding P fertilizers. Phosphorus content and Cd content of soil, maize roots and seeds were quantified. Results revealed that available soil Cd and total accumulated root and seed Cd amounts were significantly higher in TSP added treatments with and without amendments compared with ERP added soil. Considering soil available P, root and seed P, there was no significant difference observed in different treatments of TSP and ERP added treatments. A similar phenomenon was also observed in growth and yield parameters with both fertilizers added and with the added amendments. There was no colonization of AMF in maize roots in TSP applied soil while 25-60% of colonization was recorded with ERP. Synthetic fertilizer (TSP) must have inhibited the AMF colonization and thereby increasing the Cd content in maize seeds. AMF colonization increased with comparatively low soil available P in ERP added treatments. The results revealed that TSP could be effectively substituted by ERP as a source of P for maize soils. The addition of AMF, compost and biochar further increased the effect.

The impact of beech and riparian forest herbaceous plant species with contrasting traits on arbuscular mycorrhizal fungi abundance and diversity

The impact of forest herbaceous plant species identity on arbuscular mycorrhizal fungi (AMF) communities in relation to vegetation and soil chemical properties has rarely been studied in temperate forests. We thus compared abundance and diversity of AMF in two deciduous forests, in the plots with herbaceous plant species of contrasting traits (morphology, phenology, reproduction, and ecology), including Allium ursinum and Dentaria enneaphyllos in a beech forest, as well as Aegopodium podagraria and Ficaria verna in a riparian forest. Plots with a mix of herbaceous plant species and bare soil were also studied. We found low values of AMF root colonisation degrees in both forests. In total, the spores of only 13 AMF species were detected; 12 species occurred in the riparian forest, whereas 6 were found in the beech forest. AMF species composition differed between forest types. Higher AMF root colonisation degrees and soil concentrations of PLFA 16:1ω5 AMF structural lipid marker were found in the riparian forest. There were no differences between the plots in AMF abundance and species richness in both forest soils. With regard to environmental variables, the number of arbuscular mycorrhizal (AM) tree species, plant cover, moisture, the concentrations of C, Ca, K, Mg, and N had, in general, a positive effect on AMF abundance in soils. We showed that despite AMF ubiquity, these fungi can be present at low densities in some habitats, such as beech and riparian forests. Higher AMF abundance and diversity in the riparian forest were probably related to larger numbers of AM tree and herbaceous plant species in this forest. Although the herbaceous plant species had contrasting traits, they had little effect on AMF abundance and diversity.

Root Colonization and Spore Abundance of Arbuscular Mycorrhizal Fungi Along Altitudinal Gradients in Fragmented Church Natural Forest Remnants in Northern Ethiopia.

Arbuscular mycorrhizal fungi (AMF) spore density and root colonization are considered sensitive to host species and abiotic factors such as climate and soil. However, there is a knowledge gap about how fragmented native forest remnants might contribute to AMF conservation, what is the AMF spore density and root colonization, and to what extent climate change, particularly warming, might impact AMF. The aim of the study was to quantify the AMF spore density and root colonization along altitudinal gradients in three agro-ecological zones of nine church forests in northern Ethiopia. Data were collected from 45 plots. All the surveyed church forest species were colonized by AMF. However, we found a significant (p < 0.05) decrease in root colonization and AMF abundance in forests at high elevation. The topsoil had significantly (p < 0.05) higher root colonization and AMF abundance than subsurface soil. We found strong negative correlations between altitude and both spore density and root colonization and soil fertility. While we cannot separate whether spore density was temperature or soil limited, we can demonstrate the importance of conserving certain tree species, particularly Ficus species, which harbor high spore densities, in both lowland and midland church forests. In the highland, no Ficus species were found. However, Hagenia abyssinica, another Rosales, had the highest spore density in the highland ecoregion.

Co-inoculations with rhizobia and arbuscular mycorrhizal fungi alters mycorrhizal composition and lead to synergistic growth effects in cowpea that are fungal combination-dependent

Cowpea can effectively form tripartite symbiotic associations with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF) although the selection of compatible AMF species and rhizobial strains which are promoting cowpea growth remains a challenge. The aims of the current study were 1) to evaluate the response of cowpea plants to a symbiotic NFB and a multi-AMF inoculum and 2) to explore any interaction between the symbiotic NFB and the different AMF isolates. In a pot gnotobiotic trial, cowpea plants grown under limited N supply, were inoculated with or without a symbiotic nitrogen-fixing bacterium, Sinorhizobium meliloti, and combinations of three different AMF species namely Dominikia disticha, Claroideoglomus etunicatum and Rhizophagus irregularis. Experimental evaluation was determined through the measurement of above ground biomass, nutrient content and AMF root colonization. The presence of AMF species on cowpea roots was also determined with cloning and sequencing. Inoculation with both AMF and S. meliloti led to increased cowpea biomass production compared to inoculation with AMF only, but the presence of a positive effect depended on the specific AMF partners used. Inoculation with AMF alone had a highly positive impact on the growth and P uptake of cowpea, but the NFB inoculation was needed to address N deficiency in planta. The presence of both symbionts generally led to increased AMF colonization of the cowpea roots, however, plant colonization depended on the AMF species, and became even negative, when all three AMF inocula were used together. The AMF composition in plant roots was also altered in the presence of the S. meliloti. Plant nitrogen content of cowpea plants significantly increased under the presence of both symbionts compared to AMF alone, while phosphorus content was hardly affected by dual inoculations. The results show positive synergistic effects of the different AMF species and S.meliloti. Inoculation with all AMF isolates and S. meliloti led to high above ground biomass production and accumulation of N. The presence of S. meliloti increased P content in plants not inoculated with AMF. Finally, the efficiency of synergism depends on the specific AMF partners used and it is not related to their colonization levels.

Arbuscular mycorrhizal status of Erythrina brucei in different land use types in Ethiopia

Erythrina brucei is a leguminous tree commonly used in agro-forestry practices in southern and southwestern Ethiopia. It has desirable agro-forestry attributes that make it a good candidate for agro-forestry systems. However, there is a scarcity of information regarding species diversity and spore density of arbuscular mycorrhizal fungi (AMF) associated with E. brucei growing in different land use types. Therefore, this study was initiated to determine species diversity and richness in trap cultures of AMF associated with E. brucei growing in different geographic locations in various land use types of Ethiopia. Soil samples were collected from various E. brucei growing areas with different land use patterns. Trap culture was established using a portion of each soil sample by planting E. brucei as the host plant. AMF spore extraction was carried out in field and trap culture soils, and AMF species identification was done using spore morphology. Erythrina brucei root colonization with AMF structures was studied using trap culture, and AMF spore density in both field and trap culture soil samples was determined. A total of 11 AMF genera and 33 AMF species were recovered. The highest number of genera was recovered from forest land use type at Rebu Gebeya, followed by Adiskdam, live fence land use type. Glomus and Acaulospora were the dominant AMF genera covering 73% of the samples and contained 10 and 9 AMF species, respectively. All the soil samples contained indigenous AMF spore populations regardless of their origin and land use types. The highest mean AMF spore density in a field soil sample was recorded at a farmland in Bodite (280 spores 100 g−1 of dry soil), while the lowest was from Hossana (172 spores 100 g−1of dry soil). However, the highest mean AMF spore density in trap culture was detected from a farm land at Humbo (715 spores 100 g−1 of dry soil) and the lowest from Dhakallo (217 spores 100 g−1 of dry soil). Direct extraction of AMF from field soil samples showed lesser AMF spore density compared with trap culture in the same soil sample. All E. brucei root segments were colonized with the AMF structures, and the colonization status ranged from 34.4% to 49.1%. Both geographic location and land use type significantly affected AMF species richness (p < 0.05). Undisturbed land use types were characterized by high species richness. The soil pH and available phosphorus were negatively correlated to AMF spore density (p < 0.05), but AMF root colonization did not show any significant correlation. Moreover, significant correlations were also not observed between spore number and root colonization, and available phosphorus and root length colonization. We conclude that diverse and dominant AMF genera inhabited the rhizosphere of E. brucei, which can be used for the enhancement of host plant growth. To explore AMF species diversity and richness across geographic location and land use types in detail enhanced area coverage and the combination of both direct field soil and trap culture techniques are recommended.

Selection of efficient phosphorus solubilizing bacteria strains and mycorrhizea for enhanced cereal growth, root microbe status and N and P uptake in alkaline calcareous soil

ABSTRACT Calcareous, alkaline and kaolinite soils, despite external P fertilization, are low in plant extractable P because of their P fixing nature. Use of Arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB) are eco-friendly technologies for enhancing plant P nutrition and total crop production. However, use of potentially viable amongst numerous strains is of significant importance. In this study, we isolated and characterized AMF and PSB strains from berseem, wheat and pasture rhizosphere at ten agricultural soils and evaluated their P nutrition potential on maize crop grown in pots. Two PSB strains (URF-B-4 and NP-B-4) were identified for their highest population density (3.2 × 108 g−1 CFU) and P solubility index (3.02) whilst a total of four AMF strains (Glomus Hoi, Glomus claroideum, Glomus mossai, and Glomus intrardices) were isolated from berseem rhizosphere. The isolated strains were used both in the presence and absence of vermicompost (VC) in order to evaluate their potential in low and high carbon soils. Results revealed that selected strains of AMF and PSB in vermicompost (VC) pots (AMF+PSB+VC) significantly increased the plant height and roots dry biomass (by 41 and 55%, respectively). Soil OM, AB-DTPA extractable P, soil total N, plant P concentrations and N and P uptake were also significantly (P < 0.05) higher with AMF+PSB+VC followed by PSB+VC over rest of the treatments. The AMF+PSB resulted in significantly higher plant N concentration while the AMF root colonization and spores density and PSB population density were maximum for AMF+PSB+VC followed by AMF+PSB. Results concluded that for improved plant growth, nutrients availability/uptake, microbial status, and fertility of the alkaline and calcareous soils, only the efficient AMF and PSB strains (URF-B-4 and NP-B-4) application along with vermicompost would pay back significantly in addition to routine inorganic P fertilizer application.

Isabgol (Plantago ovata) and lentil (Lens culinaris) intercrop responses to arbuscular mycorrhizal fungi inoculation

ABSTRACT Intercropping medicinal plants with grain legumes provides an excellent opportunity for small-scale farmers to generate more income and move towards sustainable cropping systems. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on yield, quality and nutrient uptake of isabgol and lentil, when grown as monocrops or in various intercropping ratios, were evaluated. Inoculation with AMF resulted in positive effects on AMF root colonisation, yield components and seed yields (significant for lentils only) of both crops, especially in the intercropping systems, as well as in the nutrient uptake in isabgol. The highest seed yields of isabgol (743 kg ha−1) and lentil (684 kg ha−1) were obtained when these species were grown as monocrops and inoculated with AMF. The highest mucilage content (20.9%) and swelling factor (16.9 ml) of the isabgol seeds were found when the two secies were grown in the intercropping ratio of 2I:2L (2 rows isabgol: 2 rows lentil) and treated with AMF. Regarding the composition of the isabgol seed mucilage, the highest concentrations of galacturonic acid (9.0%), galactose (11.8%), glucuronic acid (18.3%), and xylose (39.0%) were recorded in intercropping with AMF treatment. AMF inoculation also increased soil basic microbial respiration, soil substrate-induced respiration and soil microbial biomass carbon. Overall, the highest land equivalent ratio (LER = 1.67) was recorded in the 4I:2L intercropping pattern with AMF inoculation. The results indicated that intercropping of isabgol and lentil together with AMF inoculation was an effective system to increase the use efficiency of resources for smallholder farmers in semi-arid regions.

Crop diversity enriches arbuscular mycorrhizal fungal communities in an intensive agricultural landscape.

Summary Arbuscular mycorrhizal fungi (AMF) are keystone symbionts of agricultural soils but agricultural intensification has negatively impacted AMF communities. Increasing crop diversity could ameliorate some of these impacts by positively affecting AMF. However, the underlying relationship between plant diversity and AMF community composition has not been fully resolved.We examined how greater crop diversity affected AMF across farms in an intensive agricultural landscape, defined by high nutrient input, low crop diversity and high tillage frequency. We assessed AMF communities across 31 field sites that were either monocultures or polycultures (growing > 20 different crop types) in three ways: richness, diversity and composition. We also determined root colonization across these sites.We found that polycultures drive the available AMF community into richer and more diverse communities while soil properties structure AMF community composition. AMF root colonization did not vary by farm management (monocultures vs polycultures), but did vary by crop host.We demonstrate that crop diversity enriches AMF communities, counteracting the negative effects of agricultural intensification on AMF, providing the potential to increase agroecosystem functioning and sustainability.

Effect of single and mixed inoculation of arbuscular mycorrhizal fungi and phosphorus fertilizer application on corn growth in calcareous soil

Abstract. Ishaq L, Adu Tae ASJ, Airthur MA, Bako PO. 2021. Effect of single and mixed inoculation of arbuscular mycorrhizal fungi and phosphorus fertilizer application on corn growth in calcareous soil. Biodiversitas 22: 1920-1926. Low availability of soil phosphorus (P) in calcareous soil in West Timor has become a constraint in improving plant productivity. A field experiment was carried out in the calcareous soil to investigate the effect of single and mixed indigenous arbuscular mycorrhizal fungi (AMF) inoculation and P fertilizer application on growth and yield of corn in Kupang District, East Nusa Tenggara Timur Province, Indonesia. The experiment was laid out in a split-plot design consisting of indigenous AMF inoculation as the main plots and inorganic P fertilizer rates as the sub-plot treatments. The main plot treatments were: without AMF inoculation (M0), inoculated with single AMF inoculum (M1) and inoculated with mixed AMF inocula (M2). Sub-plots consisted of four P rates namely 25% (P1), 50% (P2), 75% (P3) and 100% (P4) of the recommended inorganic superphosphate dose of 200 kg SP36 ha-1. The results showed that there were significant interactions between AMF inoculation and P fertilizer dose on AMF spore density, AMF colonization and soil available P. Results indicated a strong correlation between AMF colonization and soil available P. Inoculation of both M1 and M2 significantly increased soil available P, plant growth and yield compared to the uninoculated plant. Spore production in the two AM responded differently to P fertilizer. Low doses of inorganic P fertilizer favored spore production in M1, whereas P fertilizer sporulation in M2 was adversely affected. The percentage of AMF root colonization of M1 and M2 decreased with an increase in P fertilizer applied. Further studies need to be conducted to evaluate the effectiveness of indigenous AMF in improving plant yield at low level of inorganic fertilizer application to achieve more sustainable agricultural practice in the region.

Soil contamination with phenanthrene induces maize mycorrhiza growth suppression

Soil pollution with polycyclic aromatic hydrocarbons (PAH) such as phenanthrene is extremely detrimental to the environment and to all living organisms, which is why appropriate remediation techniques are required. Here we tested single and combination effects of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis BEG 87 and a soil amendment that results from the fermentation of organic matter through the activity of efficient microorganisms (Bokashi) on maize (Zea mays L.) growth performance, when exposed to phenanthrene. Main results showed that phenanthrene reduced total maize dry biomass, though only in mycorrhizal plants. The AMF root colonization respectively increased and decreased with Bokashi and phenanthrene. Growth suppressions in maize with AMF are common, but to our knowledge this has not been shown in combination with PAH. Possible mechanisms involved in this growth suppression could be related with increased phenanthrene uptake and hence increased plant toxicity or that phenanthrene impaired possible benefits from AMF in terms of nutrient acquisition, which could have resulted in the imbalance of the cost-benefit of the mycorrhizal association leading to growth suppression. However, the underlying mechanisms for this observed negative mycorrhiza growth response in maize when exposed to phenanthrene remains to be identified.

Interaction between mycorrhizal fungi and Meloidogyne javanica on the growth and essential oil composition of basil (Ocimum basilicum)

Plant-parasitic nematodes and arbuscular mycorrhizal fungi (AMF) have been reported to alter the yield and chemical composition of basil (Ocimum basilicum) essential oil. The aim of this study was to evaluate the effectiveness of AMF to control the root-knot nematode Meloidogyne javanica in basil and to investigate the effects of nematode-AMF interactions on plant growth, phosphorus (P) absorption, and essential oil composition. The experiment was conducted under greenhouse conditions following a completely randomized 3 × 2 factorial (two fungal species and an uninoculated control × inoculated and uninoculated seedlings) arrangement with 10 replicates. Substrates were inoculated with Claroideoglomus etunicatum, Rhizophagus clarus, or no fungi (control) and sown with basil seeds. After 20 days, half of the seedlings were inoculated with 4,000 M. javanica eggs. After 60 days, the vegetative parameters, P absorption, essential oil composition, nematode population density, AMF root-colonization efficiency, and AMF spore density were determined. The presence of AMF increased the basil’s fresh weight and ability to absorb P, while reducing the M. javanica reproduction. In total, 21 compounds were identified in basil essential oil, the concentrations of which varied according to the treatments. The major components were eucalyptol, linalool, eugenol, β-elemene, trans-α-bergamotene, and τ-cadinol. Inoculation with AMF decreased the linalool levels but increased the amount of eucalyptol. Mycorrhizal plants showed increased shoot height, P uptake, and essential oil yield and a decreased nematode population density in their roots

Mycorrhizal response strategies of trifoliate orange under well-watered, salt stress, and waterlogging stress by regulating leaf aquaporin expression

Aquaporins (AQPs) involved in water and small molecule transport respond to environmental stress, while it is not clear how arbuscular mycorrhizal fungi (AMF) regulate AQP expression. Here, we investigated the change in leaf water potential and expression level of four tonoplast intrinsic proteins (TIPs), six plasma membrane intrinsic proteins (PIPs), and four nodin-26 like intrinsic proteins (NIPs) genes in trifoliate orange (Poncirus trifoliata) inoculated with Funneliformis mosseae under well-watered (WW), salt stress (SS), and waterlogging stress (WS). Root AMF colonization and soil hyphal length collectively were reduced by SS and WS. Under WW, inoculation with AMF gave diverse responses of AQPs: six AQPs up-regulated, three AQPs down-regulated, and five AQPs did not change. Such up-regulation of more AQPs under mycorrhization and WW partly accelerated water absorption, thereby, maintaining higher leaf water potential. However, under SS, all the fourteen AQPs were dramatically induced by AMF inoculation, which improved water permeability of membranes and stimulated water transport of the host. Under WS, AMF colonization almost did not induce or even down-regulated these AQPs expressions with three exceptions (PtTIP2;2, PtPIP1;1, and PtNIP1;2), thus, no change in leaf water potential. As a result, mycorrhizal plants under flooding may have an escape mechanism to reduce water absorption. It is concluded that AMF had different strategies in response to environmental stresses (e.g. SS and WS) by regulating leaf AQP expression in the host (e.g. trifoliate orange).

Colonization by arbuscular mycorrhizal fungi improves salinity tolerance of eucalyptus (Eucalyptus camaldulensis) seedlings

Soil salinity affects soil quality and reduces plant performance. Arbuscular mycorrhizal fungi (AMF) can enhance the tolerance of plants under salinity stress. Cultivation of eucalyptus (Eucalyptus camaldulensis), which exhibits high water use efficiency, is possible in saline areas to produce raw materials for the pulp industry. We determined the effects of arbuscular mycorrhizal fungi (AMF) on the growth and survival of eucalyptus seedlings under saline conditions. Three different clones of eucalyptus seedlings were pre-inoculated with three salt-tolerant AMF species, namely Glomus sp.2, Gigaspora albida and G. decipiens, and without pre-inoculation. The seedlings were grown in a greenhouse for 45 days. They were then transferred to individual pots, filled with field soil and subsequently treated with NaCl solution until electro-conductivity (EC) reached 10, 15 and 20 dS m−1. They were watered for 90 days under nursery conditions. The results show that increased salinity levels reduced plant performance, fractional AMF root colonization, spore number, and eucalypt K/Na ratio. AMF significantly increased chlorophyll and decreased leaf proline concentrations by more than 50% and 20% respectively and increased the K/Na ratio three- to six-fold compared with non-inoculated plants. Pre-inoculation with AMF before outplanting also improved plant performance by more than 30% under salinity stress compared to non-inoculated plants. We conclude that AMF can alleviate the negative impacts of salinity on plant physiological and biochemical parameters.

Impact of Biological Fertilizer Arbuscular Mycorrhizal Fungi and Conventional Fertilizers Mobilization on Growth, Yield, Nutrients Uptake, Quercetin and Allin Contents in Allium Crops Cultivation Under Field Conditions in Semi-Arid Region of India

Field experiment was conducted at farmer field Lasalgaon in the state of Maharashtra, India to determine the influence of arbuscular mycorrhizal fungi (AMF) to reduce the doses of chemical fertilizer used in major allium crops (red onion, white onion and garlic) during winter cultivation. AMF inoc-ulated and uninoculated onion and garlic seedlings/cloves were grown with recommended dose of fertilizer (100% RDF) and Mycorrhiza +75% RDF. AMF inoculated onion and garlic plant showed significant increase in plant growth parameters like plant height, total biomass, neck thickness, bulb diameters and bulb weight. AMF + 75% RDF treatments resulted into greater plant morphological characters, highest yield, height, TSS, quercetin and allin contents and AMF root colonization as compared to uninoculated control (100% RDF). The results reveal that AMF contribute to growth and development of onion and garlic plant under field conditions. In the present study, it can be concluded that AMF could reduce the amount of chemical fertilizers to enhancing overall performance of onion and garlic and provide a sustainable and environmentally safer option for cultivation.

Arbuscular mycorrhizal colonization rate of an exotic plant, Galinsoga quadriradiata, in mountain ranges changes with altitude.

Arbuscular mycorrhizal fungi (AMF) are suggested to be important for invasions by many exotic plants. However, it is not yet known how associations between AMF and invasive plant populations change in mountains ranges and how changed associations affect further expansion of different populations in new habitats. We conducted a field survey to detect AMF colonization rate of the invasive Galinsoga quadriradiata along an elevational gradient ranging from 223 to 1947masl in the Qinling and Bashan Mountains, China. Additionally, a greenhouse experiment was conducted to compare plant growth performance among five elevational populations. In the field, total plant mass and seed production, as well as root AMF colonization rate, significantly decreased with elevation. When populations were grown in a novel soil environment in the greenhouse, the high-altitude populations achieved higher seed and total mass at lower AMF colonization rate than the low-altitude populations. Moreover, high AMF association was related to high intraspecific competition within low-altitude populations and limited seed production. Our results revealed that the associations between AMF and G. quadriradiata decrease with altitude in mountain ranges, and this may indicate that differentiation of association between AMF and elevational populations occurs during range expansion of G. quadriradiata. The results of the greenhouse experiment suggest that the high-altitude populations are more aggressive than the low-altitude populations in a non-stressful environment.

Development of a taxon-discriminating molecular marker to trace and quantify a mycorrhizal inoculum in roots and soils of agroecosystems.

Crop inoculation with Glomus cubense isolate (INCAM-4, DAOM-241198) promotes yield in banana, cassava, forages, and others. Yield improvements range from 20 to 80% depending on crops, nutrient supply, and edaphoclimatic conditions. However, it is difficult to connect yield effects with G. cubense abundance in roots due to the lack of an adequate methodology to trace this taxon in the field. It is necessary to establish an accurate evaluation framework of its contribution to root colonization separated from native arbuscular mycorrhizal fungi (AMF). A taxon-discriminating primer set was designed based on the ITS nrDNA marker and two molecular approaches were optimized and validated (endpoint PCR and quantitative real-time PCR) to trace and quantify the G. cubense isolate in root and soil samples under greenhouse and environmental conditions. The detection limit and specificity assays were performed by both approaches. Different 18 AMF taxa were used for endpoint PCR specificity assay, showing that primers specifically amplified the INCAM-4 isolate yielding a 370bp-PCR product. In the greenhouse, Urochloa brizantha plants inoculated with three isolates (Rhizophagus irregularis, R. clarus, and G. cubense) and environmental root and soil samples were successfully traced and quantified by qPCR. The AMF root colonization reached 41-70% and the spore number 4-128 per g of soil. This study demonstrates for the first time the feasibility to trace and quantify the G. cubense isolate using a taxon-discriminating ITS marker in roots and soils. The validated approaches reveal their potential to be used for the quality control of other mycorrhizal inoculants and their relative quantification in agroecosystems.

Dual inoculation of soybean with &lt;i&gt;Rhizophagus irregularis&lt;/i&gt; and commercial &lt;i&gt;Bradyrhizobium japonicum&lt;/i&gt; 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>

English

Growth response of two clones of Manihot esculenta Crantz (Cassava), TMS 30555 and TMS 30572 to Bentex T soil treatment was studied. Mycorrhizal root colonization in relation to growth parameters such as stomata size, plant water content, plant foliation, as well as height and stem circumference was examined. Bentex T, a fungicide which could be used to limit the growth of Arbuscular Mycorrhizal (AM) fungi was added to soil at the concentrations of zero 0 (control), 50, 100, 500 and 1000 µg a.i. /g soil. Growth parameters had minimal variations (pEƒ 0.05) between treatments in both clones of the plant. However, clonal differences at (pE‚ 0.01) occurred in some of the growth parameters. The level of root colonization by the AM fungi affected the growth response of the plant. The untreated soil (control) with the highest AM fungi root colonization (84%) had the least plant foliation (15 and 16) and height (34.1 and 28.5 cm) for TMS 30572 and TMS 30555, respectively. The highest values obtained for stomata size (width and length) were at 50 µg/g bentex concentration; 0.040 and 0.019mm for TMS 30572 and 0.017 and 0.007 for TMS 30555, respectively. The least value obtained for the stomata size was at the zero (0) µg/g bentex concentration. Plants from soil treated with 100 µg/g bentex T concentration had the highest amount of water; 75% for TMS 30572 and 76% for TMS 30555. The untreated soil had plants with the least amount of water. Implications of Bentex T soil treatment of cassava plants was discussed in relation to mycorrhizal colonization rating and some growth parameters of the test plant. Key words: AM fungal colonization rating, growth response, cassava, Bentex T Soil Treatment

Rhizobacteria and Arbuscular Mycorrhizal Fungi of Oil Crops (Physic Nut and Sacha Inchi): A Cultivable-Based Assessment for Abundance, Diversity, and Plant Growth-Promoting Potentials

Nowadays, oil crops are very attractive both for human consumption and biodiesel production; however, little is known about their commensal rhizosphere microbes. In this study, rhizosphere samples were collected from physic nut and sacha inchi plants grown in several areas of Thailand. Rhizobacteria, cultivable in nitrogen-free media, and arbuscular mycorrhizal (AM) fungi were isolated and examined for abundance, diversity, and plant growth-promoting activities (indole-3-acetic acid (IAA) and siderophore production, nitrogen fixation, and phosphate solubilization). Results showed that only the AM spore amount was affected by plant species and soil features. Considering rhizobacterial diversity, two classes—Alphaproteobacteria (Ensifer sp. and Agrobacterium sp.) and Gammaproteobacteria (Raoultella sp. and Pseudomonas spp.)—were identified in physic nut rhizosphere, and three classes; Actinobacteria (Microbacterium sp.), Betaproteobacteria (Burkholderia sp.) and Gammaproteobacteria (Pantoea sp.) were identified in the sacha inchi rhizosphere. Considering AM fungal diversity, four genera were identified (Acaulospora, Claroideoglomus, Glomus, and Funneliformis) in sacha inchi rhizospheres and two genera (Acaulospora and Glomus) in physic nut rhizospheres. The rhizobacteria with the highest IAA production and AM spores with the highest root-colonizing ability were identified, and the best ones (Ensifer sp. CM1-RB003 and Acaulospora sp. CM2-AMA3 for physic nut, and Pantoea sp. CR1-RB056 and Funneliformis sp. CR2-AMF1 for sacha inchi) were evaluated in pot experiments alone and in a consortium in comparison with a non-inoculated control. The microbial treatments increased the length and the diameter of stems and the chlorophyll content in both the crops. CM1-RB003 and CR1-RB056 also increased the number of leaves in sacha inchi. Interestingly, in physic nut, the consortium increased AM fungal root colonization and the numbers of offspring AM spores in comparison with those observed in sacha inchi. Our findings proved that AM fungal abundance and diversity likely rely on plant species and soil features. In addition, pot experiments showed that rhizosphere microorganisms were the key players in the development and growth of physic nut and sacha inchi.