Azospirillum brasilense and Zinc Rates Effect on Fungal Root Colonization and Yield of Wheat-Maize in Tropical Savannah Conditions.

A successful microbial inoculant can increase root colonization and establish a positive interaction with native microorganisms to promote growth and productivity of cereal crops. Zinc (Zn) is an intensively reported deficient nutrient for maize and wheat production in Brazilian Cerrado. It can be sustainably managed by inoculation with plant growth-promoting bacteria and their symbiotic association with other microorganisms such as arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE). The objective of this study was to evaluate the effect of Azospirillum brasilense inoculation and residual Zn rates on root colonization and grain yield of maize and wheat in succession under the tropical conditions of Brazil. These experiments were conducted in a randomized block design with four replications and arranged in a 5 × 2 factorial scheme. The treatments consisted of five Zn rates (0, 2, 4, 6 and 8 kg ha-1) applied from zinc sulfate in maize and residual on wheat and without and with seed inoculation of A. brasilense. The results indicated that root colonization by AMF and DSE in maize-wheat cropping system were significantly increased with interaction of Zn rates and inoculation treatments. Inoculation with A. brasilense at residual Zn rates of 4 kg ha-1 increased root colonization by AMF under maize cultivation. Similarly, inoculation with A. brasilense at residual Zn rates of 2 and 4 kg ha-1 reduced root colonization by DSE under wheat in succession. The leaf chlorophyll index and leaf Zn concentration were increased with inoculation of the A. brasilense and residual Zn rates. The inoculation did not influence AMF spore production and CO2-C in both crops. The grain yield and yield components of maize-wheat were increased with the inoculation of A. brasilense under residual Zn rates of 3 to 4 kg ha-1 in tropical savannah conditions. Inoculation with A. brasilense under residual Zn rates up to 4 kg ha-1 promoted root colonization by AMF and DSE in the maize cropping season. While the inoculation with A. brasilense under 2 and 4 kg ha-1 residual Zn rates reduced root colonization by AMF and DSE in the wheat cropping season. Therefore, inoculation with A. brasilense in combination with Zn fertilization could consider a sustainable approach to increase the yield and performance of the maize-wheat cropping system in the tropical savannah conditions of Brazil.

Influence of Intact Mycelium of Arbuscular Mycorrhizal Fungi on Soil Microbiome Functional Profile in Wheat under Mn Stress.

In the current agronomic context, the adoption of alternative forms of soil management is essential to increase crop yield. Agricultural sustainability requires practices that generate positive impacts and promote an increase in microbiome diversity as a tool to overcome adverse environmental conditions. An important ally is the indigenous arbuscular mycorrhizal fungi (AMF) that can improve plant growth and provide protection against abiotic stress such as metal toxicity. In a greenhouse experiment, this work studied the effect of wheat growth on several parameters of biological activity and functional microbiome in relation to wheat antecedent plant mycotrophy and soil disturbance under Mn stress. When the wheat was planted after highly mycotrophic plants and the soil was not previously disturbed, the results showed a 60% increase in wheat arbuscular colonization and a 2.5-fold increase in dry weight along with higher values of photosynthetic parameters and dehydrogenase activity. Conversely, soil disturbance before wheat planting increased the ß-glucosidase activity and the count of manganese oxidizers, irrespectively of antecedent plant, and decreased drastically the wheat dry weight, the AMF colonization and the chlorophyll content compared to the undisturbed treatment. These findings suggest that not only the wheat growth but also the soil functional microbiome associated is affected by the antecedent type of plant and previous soil disturbance imposed. In addition, the improvement in wheat dry weight despite Mn toxicity may rely on shifts in biological activity associated to a well-established and intact ERM early developed in the soil.

Arbuscular Mycorrhizal Symbiosis Leads to Differential Regulation of Genes and miRNAs Associated with the Cell Wall in Tomato Leaves.

Arbuscular mycorrhizal symbiosis is an association that provides nutritional benefits to plants. Importantly, it induces a physiological state allowing plants to respond to a subsequent pathogen attack in a more rapid and intense manner. Consequently, mycorrhiza-colonized plants become less susceptible to root and shoot pathogens. This study aimed to identify some of the molecular players and potential mechanisms related to the onset of defense priming by mycorrhiza colonization, as well as miRNAs that may act as regulators of priming genes. The upregulation of cellulose synthases, pectinesterase inhibitors, and xyloglucan endotransglucosylase/hydrolase, as well as the downregulation of a pectinesterase, suggest that the modification and reinforcement of the cell wall may prime the leaves of mycorrhizal plants to react faster and stronger to subsequent pathogen attack. This was confirmed by the findings of miR164a-3p, miR164a-5p, miR171e-5p, and miR397, which target genes and are also related to the biosynthesis or modification of cell wall components. Our findings support the hypothesis that the reinforcement or remodeling of the cell wall and cuticle could participate in the priming mechanism triggered by mycorrhiza colonization, by strengthening the first physical barriers upstream of the pathogen encounter.

Conversion of a High-Altitude Temperate Forest for Agriculture Reduced Alpha and Beta Diversity of the Soil Fungal Communities as Revealed by a Metabarcoding Analysis.

Land-use change is one of the most important drivers of change in biodiversity. Deforestation for grazing or agriculture has transformed large areas of temperate forest in the central highlands of Mexico, but its impact on soil fungal communities is still largely unknown. In this study, we determined how deforestation of a high-altitude temperate forest for cultivation of maize (Zea mays L.) or husbandry altered the taxonomic, phylogenetic, functional, and beta diversity of soil fungal communities using a 18S rRNA metabarcoding analysis. The true taxonomic and phylogenetic diversity at order q = 1, i.e., considering frequent operational taxonomic units, decreased significantly in the arable, but not in the pasture soil. The beta diversity decreased in the order forest > pasture > arable soil. The ordination analysis showed a clear effect of intensity of land-use as the forest soil clustered closer to pasture than to the arable soil. The most abundant fungal phyla in the studied soils were Ascomycota, Basidiomycota, and Mucoromycota. Deforestation more than halved the relative abundance of Basidiomycota; mostly Agaricomycetes, such as Lactarius and Inocybe. The relative abundance of Glomeromycota decreased in the order pasture > forest > arable soil. Symbiotrophs, especially ectomycorrhizal fungi, were negatively affected by deforestation while pathotrophs, especially animal pathogens, were enriched in the pasture and arable soil. Ectomycorrhizal fungi were more abundant in the forest soil as they are usually associated with conifers. Arbuscular mycorrhizal fungi were more abundant in the pasture than in the arable soil as the higher plant diversity provided more suitable hosts. Changes in fungal communities resulting from land-use change can provide important information for soil management and the assessment of the environmental impact of deforestation and conversion of vulnerable ecosystems such as high-altitude temperate forests.

Pioneer plant species and fungal root endophytes in metal-polluted tailings deposited near human populations and agricultural areas in Northern Mexico.

As a consequence of industrial mining activity, high volumes of tailings are scattered around Mexico. Frequently, tailings contain heavy metals (HM) which entail threats against all organisms. The aim of this research was to identify plants and root fungal endophytes in polymetallic polluted tailings with the potential to be used in strategies of bioremediation. Four deposits of mine wastes, situated in a semi-arid region near urban and semi-urban populations, and agricultural areas, were studied. The physical and chemical characteristics of substrates, accumulation of HM in plant tissues, root colonization between arbuscular mycorrizal (AMF) and dark septate endophyte (DSE) fungi, and the identification of DSE fungi isolated from the roots of two plant species were studied. Substrates from all four sites exhibited extreme conditions: high levels in sand; low water retention; poor levels in available phosphorus and nitrogen content; and potentially toxic levels of lead (Pb), cadmium (Cd), and zinc (Zn). The native plants Lupinus campestris, Tagetes lunulata, and Cerdia congestiflora, as well as the exotic Cortaderia selloana and Asphodelus fistulosus, demonstrated a relevant potential role in the phytostabilization and/or phytoextraction of Pb, Cd, and Zn, according to the accumulation of metal in roots and translocation to shoots. Roots of eleven analyzed plant species were differentially co-colonized between AMF and DSE fungi; the presence of arbuscules and microsclerotia suggested an active physiological interaction. Fourteen DSE fungi were isolated from the inner area of roots of T. lunulata and Pennisetum villosum; molecular identification revealed the predominance of Alternaria and other Pleosporales. The use of native DSE fungi could reinforce the establishment of plants for biological reclamation of mine waste in semi-arid climate. Efforts are needed in order to accelerate a vegetation practice of mine wastes under study, which can reduce, in turn, their potential ecotoxicological impact on organisms, human populations, and agricultural areas.

Mycorrhizal root colonization in maize fields is more affected by soil management and climate conditions than by plant genotype.

This work aims to characterize the arbuscular mycorrhizal association between maize genotypes and the effects of soil physical-chemical attributes on the symbiosis. A preliminary greenhouse assay evaluated five maize landraces and five conventional modern genotypes in non-sterile, low-P soil. Sixty days after sowing, we measured plant height, stem diameter, shoot and root dry biomass, root colonization structures, and shoot P concentration and total accumulation. In a second stage, a 2-year on-farm study evaluated how soil physical-chemical attributes in fields with three plant genotype groups affected the arbuscular mycorrhizal fungal symbiosis in a maize diversity microcenter in Southern Brazil. We collected soil and plant material in farms growing landrace, conventional modern genotypes, or genetically modified (GM) maize. There were five collection points at each group, and we measured mycorrhizal colonization, soil physicochemical attributes, and shoot phosphorus concentration. The greenhouse study showed that genotypes have different growth strategies for root production and shoot growth. No differences in mycorrhizal colonization rates occurred among landraces and modern maize genotypes in the low-P soil. The field study showed that soil and climate conditions had a more marked effect on mycorrhizal root colonization than plant genotype groups (landrace, conventional modern genotypes, or GM maize).

An Updated Review on the Modulation of Carbon Partitioning and Allocation in Arbuscular Mycorrhizal Plants.

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs that supply mineral nutrients to the host plant in exchange for carbon derived from photosynthesis. Sucrose is the end-product of photosynthesis and the main compound used by plants to translocate photosynthates to non-photosynthetic tissues. AMF alter carbon distribution in plants by modifying the expression and activity of key enzymes of sucrose biosynthesis, transport, and/or catabolism. Since sucrose is essential for the maintenance of all metabolic and physiological processes, the modifications addressed by AMF can significantly affect plant development and stress responses. AMF also modulate plant lipid biosynthesis to acquire storage reserves, generate biomass, and fulfill its life cycle. In this review we address the most relevant aspects of the influence of AMF on sucrose and lipid metabolism in plants, including its effects on sucrose biosynthesis both in photosynthetic and heterotrophic tissues, and the influence of sucrose on lipid biosynthesis in the context of the symbiosis. We present a hypothetical model of carbon partitioning between plants and AMF in which the coordinated action of sucrose biosynthesis, transport, and catabolism plays a role in the generation of hexose gradients to supply carbon to AMF, and to control the amount of carbon assigned to the fungus.

Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia.

Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. We used a large-scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low-fertility soils in Central Amazonia after 1 yr of fertilisation. Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. Here we showed that rock-derived nutrients determined root functioning in low-fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicated that even slow-growing tropical rainforests can respond rapidly to changes in resource availability.

The genetic architecture of host response reveals the importance of arbuscular mycorrhizae to maize cultivation.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in cultivated soils, forming symbiotic relationships with the roots of major crop species. Studies in controlled conditions have demonstrated the potential of AMF to enhance the growth of host plants. However, it is difficult to estimate the actual benefit in the field, not least because of the lack of suitable AMF-free controls. Here we implement a novel strategy using the selective incorporation of AMF-resistance into a genetic mapping population to evaluate maize response to AMF. We found AMF to account for about one-third of the grain production in a medium input field, as well as to affect the relative performance of different plant genotypes. Characterization of the genetic architecture of the host response indicated a trade-off between mycorrhizal dependence and benefit. We identified several QTL linked to host benefit, supporting the feasibility of breeding crops to maximize profit from symbiosis with AMF.

Seasonal Variation in Mycorrhizal Community of Different Cerrado Phytophysiomies.

Purpose: Understanding the dynamics of mycorrhizal fungi in the Cerrado is fundamental for the adoption of conservation practices and for understanding the resilience of this biome in relation to long periods of drought. Thus, this work aimed to verify the dynamics of the mycorrhizal population in five phytophysiognomies of the Cerrado biome. Methods: The samples were taken from the Chapada dos Veadeiros National Park, a permanent preservation with native Cerrado vegetation without any anthropic influence. The five main phytophysiognomies of the Cerrado biome were chosen: the Campo Limpo, Campo Sujo, Cerrado Strictu Sensu, Cerradão, and Veredas. Rhizospherical soil samples were collected in both the wet and dry seasons. Spore density, mycorrhizal colonization rate, easily extractable glomalin, and associated mycorrhizal fungi genera were identified. Results: The values of spore density, mycorrhizal colonization rate, and glomalin were higher in the samples performed during the dry season compared to the samples performed in the rainy season. The same behavior was observed when comparing the different phytophysionomies. Conclusion: Mycorrhizal activity is higher in dry periods when compared to rainy periods. There is no specificity of genera of arbuscular mycorrhizal fungi within the Cerrado phytophysiognomies.

Moderate phosphorus additions consistently affect community composition of arbuscular mycorrhizal fungi in tropical montane forests in southern Ecuador.

Anthropogenic atmospheric deposition can increase nutrient supply in the most remote ecosystems, potentially affecting soil biodiversity. Arbuscular mycorrhizal fungal (AMF) communities rapidly respond to simulated soil eutrophication in tropical forests. Yet the limited spatio-temporal extent of such manipulations, together with the often unrealistically high fertilization rates employed, impedes generalization of such responses. We sequenced mixed root AMF communities within a seven year-long fully factorial nitrogen (N) and phosphorus (P) addition experiment, replicated at three tropical montane forests in southern Ecuador with differing environmental characteristics. We hypothesized: strong shifts in community composition and species richness after long-term fertilization, site- and clade-specific responses to N vs P additions depending on local soil fertility and clade life history traits respectively. Fertilization consistently shifted AMF community composition across sites, but only reduced richness of Glomeraceae. Compositional changes were mainly driven by increases in P supply while richness reductions were observed only after combined N and P additions. We conclude that moderate increases of N and P exert a mild but consistent effect on tropical AMF communities. To predict the consequences of these shifts, current results need to be supplemented with experiments that characterize local species-specific AMF functionality.

Dual-mycorrhizal plants: their ecology and relevance.

Dual-mycorrhizal plants are capable of associating with fungi that form characteristic arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) structures. Here, we address the following questions: (1) How many dual-mycorrhizal plant species are there? (2) What are the advantages for a plant to host two, rather than one, mycorrhizal types? (3) Which factors can provoke shifts in mycorrhizal dominance (i.e. mycorrhizal switching)? We identify a large number (89 genera within 32 families) of confirmed dual-mycorrhizal plants based on observing arbuscules or coils for AM status and Hartig net or similar structures for EM status within the same plant species. We then review the possible nutritional benefits and discuss the possible mechanisms leading to net costs and benefits. Cost and benefits of dual-mycorrhizal status appear to be context dependent, particularly with respect to the life stage of the host plant. Mycorrhizal switching occurs under a wide range of abiotic and biotic factors, including soil moisture and nutrient status. The relevance of dual-mycorrhizal plants in the ecological restoration of adverse sites where plants are not carbon limited is discussed. We conclude that dual-mycorrhizal plants are underutilized in ecophysiological-based experiments, yet are powerful model plant-fungal systems to better understand mycorrhizal symbioses without confounding host effects.

Efectividad de hongos micorrizo-arbusculares nativos en suelos con diferentes usos agropecuarios / Native arbuscular mycorrhizal fungi effectiveness in soils with different agricultural uses

RESUMEN Objetivo. Determinar la efectividad de hongos micorrizo-arbusculares (HMA) de suelos con diferentes usos agropecuarios, en el valle medio del río Sinú, Colombia. Materiales y métodos. Bajo condiciones de invernadero se realizó el experimento, donde se utilizó como planta indicadora Leucaena leucocephala, la cual se sembró en materos con suelo de un Andisol (horizonte B) usado como sustrato. Este sustrato, se inoculó separadamente con muestras de siete suelos (horizonte Ap), como fuente de HMA, provenientes del Centro de Investigación Turipaná de Agrosavia. Como controles se incluyeron inoculación con HMA Glomus fasciculatum y uno no-inoculado El efecto de la inoculación micorrizal se evaluó mediante el monitoreo del contenido de P foliar en las plantas de L. leucocephala, en función del tiempo hasta 64 días cuando se determinó la masa seca de su parte aérea y la colonización micorrizal. Resultados. El crecimiento de L. leucocephala y el contenido de P foliar fue significativamente superior cuando el suelo se inoculó con G. fasciculatum, en comparación a aquel observado con los demás tratamientos. De igual forma, la colonización micorrizal fue muy alta en las raíces de L. leucocephala que crecieron en el suelo inoculado con G. fasciculatum e inferior en los otros tratamientos. Conclusiones. Los resultados indican que los HMA nativos de suelos con diferentes usos, provenientes del C.I Turipaná de Agrosavia, exhibieron bajo potencial para desarrollar simbiosis micorrizal, lo que limitó el crecimiento y la concentración de P foliar en la planta hospedera.

ABSTRACT Objective. To determine the effectiveness of mycorrhizal-arbuscular fungi (AMF) of soils with different agricultural uses, in the middle valley of the Sinú river, Colombia. Materials and methods. The experiment was carried out under greenhouse conditions, where Leucaena leucocephala was used as the indicator plant, which was planted in masons with an Andisol soil (horizon B) used as a substrate. This substrate was inoculated separately with samples from seven soils (Ap horizon), as a source of AMF, from the Turipaná Research Center in Agrosavia. As controls we included inoculation with HMA Glomus fasciculatum and one non-inoculated one. The effect of mycorrhizal inoculation was evaluated by monitoring the foliar P content in L. leucocephala plants, as a function of time to 64 days, when the dry mass of its aerial part and mycorrhizal colonization was determined. Results. The growth of L. leucocephala and the foliar P content was significantly higher when the soil was inoculated with G. fasciculatum, in comparison to that observed with the other treatments. Likewise, mycorrhizal colonization was very high in the roots of L. leucocephala that grew in the soil inoculated with G. fasciculatum and lower in the other treatments. Conclusions. The results indicate that the native AMF of soils with different uses, from Turipaná, exhibited low potential to develop mycorrhizal symbiosis, which limited the growth and concentration of leaf P in the host plant.

Subterranean Desert Rodents (Genus Ctenomys) Create Soil Patches Enriched in Root Endophytic Fungal Propagules.

Subterranean rodents are considered major soil engineers, as they can locally modify soil properties by their burrowing activities. In this study, the effect of a subterranean rodent of the genus Ctenomys on soil properties and root endophytic fungal propagules in a shrub desert of northwest Argentina was examined. Our main goal was to include among root endophytic fungi not only arbuscular mycorrhiza but also the dark septate endophytes. We compared the abundance of fungal propagules as well as several microbiological and physicochemical parameters between soils from burrows and those from the surrounding landscape. Our results show that food haulage, the deposition of excretions, and soil mixing by rodents' burrowing promote soil patchiness by (1) the enrichment in both types of root endophytic fungal propagules; (2) the increase in organic matter and nutrients; and (3) changes in soil edaphic properties including moisture, field capacity, and texture. These patches may play a critical role as a source of soil heterogeneity in desert ecosystems, where burrows constructed in interpatches of bare soil can act, once abandoned, as "islands of fertility," promoting the establishment of plants in an otherwise hostile environment.

Maize Productivity, Mycorrhizal Assessment, Chemical and Microbiological Soil Attributes Influenced by Maize-Forage Grasses Intercropping

Abstract Mycorrhizae are important components of agroecosystems and the diversification of crops stimulates the abundance of arbuscular mycorrhizal fungi and the participation of symbiosis in plant growth. This experiment examined mycorrhizal assessment, chemical and microbiological soil attributes in a maize-forage grasses intercropping compared to a maize-monocropping system. A complete randomized block design was used with crop systems installed under no-till management with three replicates, as follow: Maize (Zea mays L.); Panicum maximum Jacq. cv. Aruana; Urochloa humidicola (Rendle.) Schweickerdt.; Maize-P. maximum intercropping and Maize-U. humidicola intercropping. In 2015/2016 season, intercropping maize with Panicum maximum Jacq. cv. Aruana or Urochloa humidicola (Rendle.) Schweickerdt. promoted similar effects (Tukey test, p<0.05) to monocropped maize under no-till system on soil chemical and biochemical parameters related to carbon cycling in the soil surface layer, as well as the dynamics of arbuscular mycorrhizal symbiosis in tropical soils, managed for a period of more than six years. Similar grain yield was verified among maize crop systems. This result indicates that intercropping maize-tropical forage grasses represents an alternative for monocropped grains, a very common practice that is used in intensive management, being able to guarantee equivalent productivities and to combine grain production with crop-livestock systems. As a result, intercropping promotes the diversification of the property's income source, adding environmental gains, such as more efficient land use by cultivated plants, keeping soil constantly cultivated, storing carbon and contributing to minimize the impact of climate change on agricultural systems and the sustainability of food production.

Wetland plant species improve performance when inoculated with arbuscular mycorrhizal fungi: a meta-analysis of experimental pot studies.

The presence of arbuscular mycorrhizal fungi (AMF) in wetlands is widespread. Wetlands are transition ecosystems between aquatic and terrestrial systems, where shallow water stands or moves over the land surface. The presence of AMF in wetlands suggests that they are ecologically significant; however, their function is not yet clearly understood. With the aim of determining the overall magnitude and direction of AMF effect on wetland plants associated with them in pot assays, we conducted a meta-analysis of data extracted from 48 published studies. The AMF effect on their wetland hosts was estimated through different plant attributes reported in the studies including nutrient acquisition, photosynthetic activity, biomass production, and saline stress reduction. As the common metric, we calculated the standardized unbiased mean difference (Hedges' d) of wetland plant performance attributes in AMF-inoculated plants versus non-AMF-inoculated plants. Also, we examined a series of moderator variables regarding symbiont identity and experimental procedures that could influence the magnitude and direction of an AMF effect. Response patterns indicate that wetland plants significantly benefit from their association with AMF, even under flooded conditions. The beneficial AMF effect differed in magnitude depending on the plant attribute selected to estimate it in the published studies. The nature of these benefits depends on the identity of the host plant, phosphorus addition, and water availability in the soil where both symbionts develop. Our meta-analysis synthetizes the relationship of AMF with wetland plants in pot assays and suggests that AMF may be of comparable importance to wetland plants as to terrestrial plants.

ESTIMULACIÓN DE GERMINACIÓN Y COLONIZACIÓN RADICULAR DE Diversispora trimulares POR FLAVONOIDES DE EXUDADOS RADICULARES DE Nicotiana glauca / STIMULATION OF GERMINATION OF SPORES AND ROOT COLONIZATION OF Diversispora trimulares BY FLAVONOIDS IN Nicotiana glauca ROOT EXUDATES

Los metabolitos secundarios son señales importantes en la interacción planta-microrganismos; sin embargo, los datos que corroboran el rol de los flavonoides como señales entre plantas y la simbiosis micorrízica arbuscular son limitados y aún recientes. Este estudio tiene por objetivo evaluar el efecto de flavonoides presentes en exudados radiculares de Allium porrum L., Nicotiana gluaca y Brassica oleracea var. Itálica, en la germinación de esporas y establecimiento de colonización radicular de Diversispora trimulares. Se detectaron miricetina y canferol en exudados de A. porrum, con un contenido total de flavonoides de 23,80µg g-1, de raíz seca; quercetina, en N. glauca, con 23,35µg g-1 y crisina, en B. oleracea, con 14,71µg g-1. Quercetina estimuló la germinación y la vitalidad de esporas (24%, 40%), a diferencia de crisina, que presentó un efecto inhibitorio (4%, 20%). A. porrum y N. glauca incrementaron la germinación de esporas (54%, 56%) y porcentaje de colonización de micorriza arbuscular (72%, 75%). Los resultados de la investigación mostraron una evidencia sólida del efecto de los flavonoides como moléculas estimulantes en los procesos de germinación de esporas y colonización de micorriza arbuscular.

Secondary metabolites are important signals that could determine the outcome of the plant soil microbial interactions, however, the data available that support the leading role of flavonoids in the communication of arbuscular mycorrhizal symbiosis are recent and limited. The present study examines the effect of flavonoids detected in root exudates from Allium porrum, Nicotiana glauca y Brassica oleracea var. italica on spore germination and mycorrhizal root colonization of Diversispora trimulares. Myricetin and kaempferol were detected in A. porrum root exudates with a total flavonoid content of 23.80µg g-1 dried root, quercetin in N. glauca with 23,35µg g-1 and chrysin in B. Oleracea with 14.71 µg g-1. Quercetin increased the spore germination and vitality (24%, 40%). In contrast, chrysin showed an inhibitory effect (4%, 20%). A. porrum and N. glauca increased spore germination (54%, 56%) and root mycorrhizal colonization (72%, 75%). This results evidence the effect of flavonoids on the stimulization of spore germination and stablishment of root colonization of arbuscular mycorrhizal fungi.

Arbuscular and Ectomycorrhizal Fungi Associated with the Invasive Brazilian Pepper Tree (Schinus terebinthifolius) and Two Native Plants in South Florida.

The potential role of soil fungi in the invasion of the Brazilian pepper tree (Schinus terebinthifolius-BP) in Florida is not known; although the low biotic resistance of Florida soils is often invoked to explain the prevalence of many invasive species. To gain an initial insight into BP's mycorrhizal associations, this study examined the rhizobiome of BP and two native plants (Hamelia patens and Bidens alba) across six locations. Arbuscular mycorrhizal fungi (AMF) associated with the roots of the target plants and bulk soil was characterized by spore morphotyping. Sequence analysis of metagenomic DNA from lateral roots/rhizosphere of BP (n = 52) and a native shrub H. patens (n = 37) on the same parcel yielded other fungal associates. Overall, the total population of AMF associated with BP was about two folds greater than that of the two native plants (p = 0.0001) growing on the same site. The dominant AMF under Schinus were members of the common Glomus and Rhizophagus spp. By contrast, the most prevalent AMF in the bulk soil and rhizosphere of the two Florida native plants, Acaulospora spp (29%) was sharply diminished (9%) under BP rhizosphere. Analysis of the ITS2 sequences also showed that Schinus rhizosphere had a high relative abundance of ectomycorrhizal fungi (76.5%) compared to the native H. patens (2.6%), with the species Lactifluus hygrophoroides (Basidiomycota) being the most prevalent at 61.5% (p < 0.05). Unlike the native plants where pathogenic fungi like Phyllosticta sp., Phoma sp., and Neofusicoccum andium were present (8.1% for H. patens), only one potentially pathogenic fungal taxon was detected (3.9%) under BP. The striking disparity in the relative abundance of AMF and other fungal types between BP and the native species is quite significant. Fungal symbionts could aide plant invasion via resource-use efficiency and other poorly defined mechanisms of protection from pathogens in their invaded range. This report exposes a potentially significant but previously unappreciated fungal dimension of a complex invasion system and underscores the need to characterize these fungal symbionts, their role and mode of action during invasion; with the goal of devising measures for invasion control and ecological restoration.

Gene expression analyses in tomato near isogenic lines provide evidence for ethylene and abscisic acid biosynthesis fine-tuning during arbuscular mycorrhiza development.

Plant responses to the environment and microorganisms, including arbuscular mycorrhizal fungi, involve complex hormonal interactions. It is known that abscisic acid (ABA) and ethylene may be involved in the regulation of arbuscular mycorrhiza (AM) and that part of the detrimental effects of ABA deficiency in plants is due to ethylene overproduction. In this study, we aimed to determine whether the low susceptibility to mycorrhizal colonization in ABA-deficient mutants is due to high levels of ethylene and whether AM development is associated with changes in the steady-state levels of transcripts of genes involved in the biosynthesis of ethylene and ABA. For that, tomato (Solanum lycopersicum) ethylene overproducer epinastic (epi) mutant and the ABA-deficient notabilis (not) and sitiens (sit) mutants, in the same Micro-Tom (MT) genetic background, were inoculated with Rhizophagus clarus, and treated with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The development of AM, as well as the steady-state levels of transcripts involved in ethylene (LeACS2, LeACO1 and LeACO4) and ABA (LeNCED) biosynthesis, was determined. The intraradical colonization in epi, not and sit mutants was significantly reduced compared to MT. The epi mutant completely restored the mycorrhizal colonization to the levels of MT with the application of 10 µM of AVG, probably due to the inhibition of the ACC synthase gene expression. The steady-state levels of LeACS2 and LeACO4 transcripts were induced in mycorrhizal roots of MT, whereas the steady-state levels of LeACO1 and LeACO4 transcripts were significantly induced in sit, and the steady-state levels of LeNCED transcripts were significantly induced in all genotypes and in mycorrhizal roots of epi mutants treated with AVG. The reduced mycorrhizal colonization in sit mutants seems not to be limited by ethylene production via ACC oxidase regulation. Both ethylene overproduction and ABA deficiency impaired AM fungal colonization in tomato roots, indicating that, besides hormonal interactions, a fine-tuning of each hormone level is required for AM development.