Mycorrhiza

The first in vitro aseptic synthesis of Abies firma Sieb. et Zucc. with Pisolithus tinctorius (Pers.) Coker & Couch is reported. Techniques were improved for the aseptic synthesis of ectomycorrhizas of A. firma, a slow-growing species in vitro, and Pisolithus tinctorius using a novel culture medium and both sterilized and re-rooted seedlings. After 2-3 months incubation, ectomycorrhizas were formed by both methods. The mycorrhizas possessed a mantle and a highly branched nonseptate Hartig net mycelium colonizing the intercellular spaces within the host cortex, features characteristic of ectomycorrhizas. These techniques will prove useful for addressing physiological and biochemical questions on the interactions of microbes with roots of whole plants.

Endemic populations of Abies religiosa (fir, oyamel) have great economic, ecological and social importance; in addition, they form different interactions with edaphic microorganisms, mainly with ectomycorrhizal fungi. Currently, isolated populations (i. e. fir) are threatened by deforestation, agricultural expansion and global warming; therefore, it is urgent to understand the ecological and evolutionary interactions with ectomycorrhizal fungi. The objective of the present research was to analyze the use of molecular ecology, taxonomy and biology of ectomycorrhizal
fungi to understand the role that these fungi play in A. religiosa trees in Mexico. Areas of research are presented as well as the main information gaps in the morphological/molecular characterization, taxonomy and evolution of the ectomycorrhizal symbiosis in A. religiosa. For the above, we collected information of 108 taxa of potentially ectomycorrhizal fungi obtained from different fir populations. The taxa with high potential to inoculate A. religiosa are Sebacina dimitica, Clavulina cf. cinerea, Membranomyces sp., Thelephoraceae, Russula spp., Ramaria spp., Lactarius spp. e Inocybe spp. Finally, we discuss issues that remain unresolved to determine their potential for use, management and conservation of A. religiosa in temperate areas of Mexico. This problem can be solved by combining molecular tools with the morphological and histological description of ectomycorrhizal morphotypes. In addition, methodologies are required to standardize results to come to more robust conclusions about mycorrhizal interactions.
Las poblaciones endémicas de Abies religiosa (abeto, oyamel) poseen gran importancia económica, ecológica y social; además, forman distintas interacciones con microorganismos edáficos, principalmente con hongos ectomicorrizógenos. Actualmente, las poblaciones aisladas (i. e. oyamel) están amenazadas por la deforestación, la expansión agrícola y el calentamiento global; por lo cual, es urgente entender las interacciones ecológicas y evolutivas con hongos ectomicorrizógenos. El objetivo de la presente investigación fue analizar el uso de la ecología, taxonomía y biología molecular de ectomicorrizas para comprender el papel que juegan estos hongos en árboles de A. religiosa en México. Se presentan áreas de oportunidad de investigación, así como los principales vacíos de información de la caracterización morfoanatómica/molecular, taxonomía y evolución de la simbiosis ectomicorrízica en bosques de A. religiosa. Para lo anterior, se reunió información de 108 taxones de hongos potencialmente ectomicorrizógenos, colectados en diferentes poblaciones de abetos. Los taxones con potencial alto para inocular A. religiosa son Sebacina dimitica, Clavulina cf. cinerea, Membranomyces sp., Thelephoraceae, Russula spp., Ramaria spp., Lactarius spp. e Inocybe spp. Finalmente, se discuten aspectos que faltan por resolver para determinar el potencial de uso, manejo, conservación y aprovechamiento de A. religiosa
en zonas templadas de México. Este problema puede resolverse combinando herramientas moleculares con la descripción morfológica e histológica de morfotipos ectomicorrizógenos. Adicionalmente, se requieren metodologías que permitan estandarizar resultados para llegar a conclusiones más sólidas sobre las interacciones micorrízicas.

The diversity, ecology and function of ectomycorrhizal (EM) fungi and ectomycorrhizas (ECMs) on tropical African tree species are reviewed here. While ECMs are the most frequent mycorrhizal type in temperate and boreal forests, they concern an economically and ecologically important minority of plants in African tropical forests. In these African tropical forests, ECMs are found mainly on caesalpionioid legumes, Sarcolaenaceae, Dipterocarpaceae, Asterpeiaceae, Phyllantaceae, Sapotaceae, Papilionoideae, Gnetaceae and Proteaceae, and distributed in open, gallery and rainforests of the Guineo-Congolian basin, Zambezian Miombo woodlands of East and South-Central Africa and Sudanian savannah woodlands of the sub-sahara. Overall, EM status was confirmed in 93 (26%) among 354 tree species belonging to EM genera. In addition, 195 fungal taxa were identified using morphological descriptions and sequencing of the ML5/ML6 fragment of sporocarps and ECMs from West Africa. Analyses of the belowground EM fungal communities mostly based on fungal internal transcribed spacer sequences of ECMs from Continental Africa, Madagascar and the Seychelles also revealed more than 350 putative species of EM fungi belonging mainly to 18 phylogenetic lineages. As in temperate forests, the /russula-lactarius and /tomentellathelephora lineages dominated EM fungal flora in tropical Africa. A low level of host preference and dominance of multi-host fungal taxa on different African adult tree species and their seedlings were revealed, suggesting a potential for the formation of common ectomycorrhizal networks. Moreover, the EM inoculum potential in terms of types and density of propagules (spores, sclerotia, EM root fragments and fragments of mycelia strands) in the soil allowed opportunistic root colonisation as well as long-term survival in the soil during the dry season. These are important characteristics when choosing an EM fungus for field application. In this respect, Thelephoroid fungal sp. XM002, an efficient and competitive broad host range EM fungus, possessed these characteristics and appeared to be a good candidate for artificial inoculation of Caesalps and Phyllanthaceae seedlings in nurseries. However, further efforts should be made to assess the genetic and functional diversity of African EM fungi as well as the EM status of unstudied plant species and to strengthen the use of efficient and competitive EM fungi to improve production of ecologically and economically important African multipurpose trees in plantations.

Soil acidity is an impediment to agricultural production on a significant portion of arable land worldwide. Low productivity of these soils is mainly due to nutrient limitation and the presence of high levels of aluminium (Al), which causes deleterious effects on plant physiology and growth. In response to acidic soil stress, plants have evolved various mechanisms to tolerate high concentrations of Al in the soil solution. These strategies for Al detoxification include mechanisms that reduce the activity of Al 3+ and its toxicity, either externally through exudation of Al-chelating compounds such as organic acids into the rhizosphere or internally through the accumulation of Al-organic acid complexes sequestered within plant cells. Additionally, root colonization by symbiotic arbuscular mycorrhizal (AM) fungi increases plant resistance to acidity and phytotoxic levels of Al in the soil environment. In this review, the role of the AM symbiosis in increasing the Al resistance of plants in natural and agricultural ecosystems under phytotoxic conditions of Al is discussed. Mechanisms of Al resistance induced by AM fungi in host plants and variation in resistance among AM fungi that contribute to detoxifying Al in the rhizosphere environment are considered with respect to altering Al bioavailability.

Salt stress limits crop yield and sustainable agriculture in most arid and semiarid regions of the world. Arbuscular mycorrhizal fungi (AMF) are considered bioameliorators of soil salinity tolerance in plants. In evaluating AMF as significant predictors of mycorrhizal ecology, precise quantifiable changes in plant biomass and nutrient uptake under salt stress are crucial factors. Therefore, the objective of the present study was to analyze the magnitude of the effects of AMF inoculation on growth and nutrient uptake of plants under salt stress through meta-analyses. For this, data were compared in the context of mycorrhizal host plant species, plant family and functional group, herbaceous vs. woody plants, annual vs. perennial plants, and the level of salinity across 43 studies. Results indicate that, under saline conditions, AMF inoculation significantly increased total, shoot, and root biomass as well as phosphorous (P), nitrogen (N), and potassium (K) uptake. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase also increased significantly in mycorrhizal compared to nonmycorrhizal plants growing under salt stress. In addition, sodium (Na) uptake decreased significantly in mycorrhizal plants, while changes in proline accumulation were not significant. Across most subsets of the data analysis, identities of AMF (Glomus fasciculatum) and host plants (Acacia nilotica, herbs, woody and perennial) were found to be essential in understanding plant responses to salinity stress. For the analyzed dataset, it is concluded that under salt stress, mycorrhizal plants have extensive root traits and mycorrhizal morphological traits which help the uptake of more P and K, together with the enhanced production of antioxidant enzymes resulting in salt stress alleviation and increased plant biomass.

A quantitative real-time PCR (qPCR) marker Ta0 with hydrolysis probe ("TaqMan"), targeted to the internal transcribed spacer region of the ribosomal DNA, has been developed for quantification of summer truffle (Tuber aestivum) mycelium. Gene copy concentrations determined by the qPCR were calibrated against pure culture mycelium of T. aestivum, enabling quantification of the mycelium in soil and in host roots from the fields. Significant concentrations of the fungus were observed not only in the finest roots with ectomycorrhizae but also in other root types, indicating that the fungus is an important component of the microbial film at the root surface. The concentration of T. aestivum in soil is relatively high compared to other ectomycorrhizal fungi. To evaluate the reliability of the measurement of the soil mycelium density using qPCR, the steady basal extracellular concentration of the stabilized T. aestivum DNA should be known and taken into account. Therefore, we addressed the stability of the qPCR signal in soil subjected to different treatments. After the field soil was sieved, regardless of whether it was dried/ rewetted or not, the T. aestivum DNA was quickly decomposed. It took just about 4 days to reach a steady concentration. This represents a conserved pool of T. aestivum DNA and determines detection limit of the qPCR quantification in our case. When the soil was autoclaved and recolonized by saprotrophic microorganisms, this conserved DNA pool was eliminated and the soil became free of T. aestivum DNA.

Understanding the mechanisms that underlie nutrient use efficiency and carbon allocation along with mycorrhizal interactions is critical for managing croplands and forests soundly. Indeed, nutrient availability, uptake and exchange in biotrophic interactions drive plant growth and modulate biomass allocation. These parameters are crucial for plant yield, a major issue in the context of high biomass production. Transport processes across the polarized membrane interfaces are of major importance in the functioning of the established mycorrhizal association as the symbiotic relationship is based on a 'fair trade' between the fungus and the host plant. Nutrient and/or metabolite uptake and exchanges, at biotrophic interfaces, are controlled by membrane transporters whose regulation patterns are essential for determining the outcome of plant-fungus interactions and adapting to changes in soil nutrient quantity and/or quality. In the present review, we summarize the current state of the art regarding transport systems in the two major forms of mycorrhiza, namely ectoand arbuscular mycorrhiza.

A greenhouse investigation was conducted to determine the effect of arbuscular mycorrhiza and drought on the growth of two tropical hedgerow legume trees (Gliricidia sepium and Leucaena leucocephala) under simulated eroded soil conditions. It was a factorial design with two levels of watering regime (adequate watering and drought), inoculation with Glomus deserticola

The influence of plant functional groups and moderate seasonality on arbuscular mycorrhizal (AM) fungal status (root colonization and spore density) was investigated during 13 consecutive months in a chronosequence of succession in southern Brazil, consisting of grassland field, scrub vegetation, secondary forest and mature forest, in a region of transition from tropical to subtropical zones. AM root colonization and spore density decreased with advancing succession and were highest in early successional sites with grassland and scrub vegetation, intermediary in the secondary forest and lowest in the mature forest. They were little influenced by soil properties, but were sufficiently influenced by the fine root nutrient status and fine root traits among different functional plant groups. AM root colonization and spore density were higher during the favourable plant growth season (spring and summer) than during the less favourable plant growth season (autumn and winter). Spore density displayed significant seasonal variation at all sites, whilst root colonization displayed significant seasonal variation in grassland, scrub and secondary forest, but not in mature forest. The data suggest that (1) different plant functional groups display different relationships with AM fungi, influencing their abundance differentially; (2) plant species from early successional phases are more susceptible to AM root colonization and maintain higher AM sporulation than late successional species; (3) fine root traits and nutrient status influence these AM fungal attributes; and (4) higher AM spore production and root colonization is associated with the season of higher light incidence and temperature, abundant water in soil and higher plant metabolic activity.

Abies religiosa (abeto, oyamel) tiene importancia económica por su madera y porque es usada como árbol de navidad. En los inventarios micológicos de bosque de Abies se han encontrado unas 50 especies que pueden formar ectomicorriza con A. religiosa, sin embargo, no se había estudiado específicamente este aspecto. En este trabajo se estudiaron los hongos ectomicorrízicos asociados con individuos adultos de A. religiosa en el bosque y se realizó un seguimiento de la presencia de micorriza en raíces de plántulas en el campo a través de un año. También se evaluó el efecto de cuatro tratamientos de inducción de micorriza con suelo rizosférico como inóculo sobre las variables: presencia y tipo de micorriza, altura total, diámetro a la altura de la base (Db), biomasa (B) y área foliar (Af). Se registraron 25 taxa de hongos ectomicorrízicos (24 Basidiomycota y 1 Ascomycota). Ocho fueron registrados exclusivamente en sitios con dosel y 15 en área abierta. Amanita muscaria y Russula olivacea se recolectaron en ambas condiciones. Los géneros con mayor número de taxa fueron Cortinarius (5) y Russula (4). Las especies más abundantes fueron Lycoperdon perlatum y A. muscaria. La diversidad fue significativamente mayor (p<0.001) en área abierta (H´= 3. 97) que bajo el dosel (H´= 2.8). Se encontraron estructuras micorrízicas en plántulas de A. religiosa aún cuando no se encontraron esporomas. En cuanto al experimento, la mayor tasa de crecimiento en altura (2.215 ± 0.092 cm), Db (0.825 ± 0.042 mm), B (0.446 ± 0.397 g), y Af (29.027 cm2 ± 8.947)(p < 0.01), se obtuvo en el tratamiento de suelo de A. religiosa (SA). No obstante, después de siete meses el suelo rizosférico mostró ser poco eficaz para inducir la formación de micorriza en plántulas de A. religiosa. Las diferencias en las tasas de crecimiento son atribuibles al mayor contenido de materia orgánica en el tratamiento SA. Se requiere hacer estudios en campo sobre plántulas inoculadas en invernadero para evaluar el efecto de la inoculación en la supervivencia y el desempeño de dichas plántulas.