TETRASPANIN 8-1 from Phaseolus vulgaris plays a key role during mutualistic interactions.

Arbuscular mycorrhizal (AM) fungi and rhizobia form two of the most important plant-microbe associations for the assimilation of phosphorus (P) and nitrogen (N). Symbiont-derived signals are able to coordinate the infection process by triggering multiple responses in the plant root, such as calcium influxes and oscillations, increased reactive oxygen species (ROS), cytoskeletal rearrangements and altered gene expression. An examination was made of the role of tetraspanins, which are transmembrane proteins that self-organize into tetraspanin web regions, where they recruit specific proteins into platforms required for signal transduction, membrane fusion, cell trafficking, and ROS generation. In plant cells, tetraspanins are scaffolding proteins associated with root radial patterning, biotic and abiotic stress responses, cell fate determination, plasmodesmata and hormonal regulation. Some plant tetraspanins, such as Arabidopsis thaliana TETRASPANIN 8 and TETRASPANIN 9 (AtTET8 and AtTET9) are associated with exosomes during inter-kingdom communication. In this study, a homolog of AtTET8, PvTET8-1, in common bean (Phaseolus vulgaris L. var. Negro Jamapa) was examined in roots during interactions with Rhizobium tropici and Rhizophagus irregularis. The promoter of PvTET8-1 contained several cis-acting regulatory DNA elements potentially related to mutualistic interactions, and PvTET8-1 was transcriptionally activated during AM fungal and rhizobial associations. Silencing it decreased the size and number of nodules, nitrogen fixation, and mycorrhizal arbuscule formation, whereas overexpressing it increased the size and number of nodules, and mycorrhizal arbuscule formation but decreased nitrogen fixation. PvTET8-1 appears to be an important element in both of these mutualistic interactions, perhaps through its interaction with NADPH oxidase and the generation of ROS during the infection processes.

Arbuscular mycorrhizal fungi inoculation stimulates the production of foliar secondary metabolites in Passiflora setacea DC.

Passiflora setacea DC. growing is of interest to the herbal industries since in its leaves are produced secondary metabolites that confer antioxidant, anxiolytic, and antidepressant properties in Passiflora. Therefore, it is important to search for sustainable alternatives that aim to enhance the production of these compounds to add value to the phytomass, such as the inoculation with arbuscular mycorrhizal fungi (AMF) and the application of coconut coir dust, which has not been reported to P. setacea yet. The aim was to select the efficient combination of AMF and coconut coir dust to increase the compounds' production and optimize the antioxidant activity in P. setacea leaves. The P. setacea seedlings that were cultivated in substrates without coconut coir dust and colonized by Gigaspora albida N.C. Schenck & G.S. Sm. produced more total saponins (1,707.43%), total tannins (469.98%), and total phenols (85.81%), in comparison to the non-mycorrhizal plants, in addition to enhancing the glomalin-related soil proteins. On the other hand, in general, the use of coir dust as a substrate has not been shown to increase the production of these bioactive compounds. It is concluded that the production of P. setacea seedlings using G. albida is an alternative to offer phytomass to the herbal medicines industry based on passion fruit.

Effect of Arbuscular Mycorrhizal Colonization on Cadmium-Mediated Oxidative Stress in Glycine max (L.) Merr.

Cadmium is a heavy metal (HM) that inhibits plant growth and leads to death, causing great losses in yields, especially in Cd hyperaccumulator crops such as Glycine max (L.) Merr. (soybean), a worldwide economically important legume. Furthermore, Cd incorporation into the food chain is a health hazard. Oxidative stress (OS) is a plant response to abiotic and biotic stresses with an intracellular burst of reactive oxygen species (ROS) that causes damage to lipids, proteins, and DNA. The arbuscular mycorrhizal fungal (AMF) association is a plant strategy to cope with HM and to alleviate OS. Our aim was to evaluate the mitigation effects of mycorrhization with AMF Rhizophagus intraradices on soybean growth, nutrients, Cd accumulation, lipid peroxidation, and the activity of different antioxidant agents under Cd (0.7-1.2 mg kg-1 bioavailable Cd) induced OS. Our results suggest that glutathione may act as a signal molecule in a defense response to Cd-induced OS, and mycorrhization may avoid Cd-induced growth inhibition and reduce Cd accumulation in roots. It is discussed that R. intraradices mycorrhization would act as a signal, promoting the generation of a soybean cross tolerance response to Cd pollution, therefore evidencing the potential of this AMF association for bioremediation and encouragement of crop development, particularly because it is an interaction between a worldwide cultivated Cd hyperaccumulator plant and an AMF-HM-accumulator commonly present in soils.

Transcriptome analysis of the differential effect of the NADPH oxidase gene RbohB in Phaseolus vulgaris roots following Rhizobium tropici and Rhizophagus irregularis inoculation.

BACKGROUND: Reactive oxygen species (ROS) are generated by NADPH oxidases known as respiratory burst oxidase homologs (RBOHs) in plants. ROS regulate various cellular processes, including the mutualistic interactions between legumes and nitrogen-fixing bacteria or arbuscular mycorrhizal (AM) fungi. Rboh is a multigene family comprising nine members (RbohA-I) in common bean (Phaseolus vulgaris). The RNA interference-mediated silencing of RbohB (PvRbohB-RNAi) in this species diminished its ROS production and greatly impaired nodulation. By contrast, the PvRbohB-RNAi transgenic roots showed early hyphal root colonization with enlarged fungal hypopodia; therefore, we proposed that PvRbohB positively regulates rhizobial infection (Rhizobium tropici) and inhibits AM colonization by Rhizophagus irregularis in P. vulgaris. RESULTS: To corroborate this hypothesis, an RNA-Seq transcriptomic analysis was performed to identify the differentially expressed genes in the PvRbohB-RNAi roots inoculated with Rhizobium tropici or Rhizophagus irregularis. We found that, in the early stages, root nodule symbioses generated larger changes of the transcriptome than did AM symbioses in P. vulgaris. Genes related to ROS homeostasis and cell wall flexibility were markedly upregulated in the early stages of rhizobial colonization, but not during AM colonization. Compared with AM colonization, the rhizobia induced the expression of a greater number of genes encoding enzymes involved in the metabolism of auxins, cytokinins, and ethylene, which were typically repressed in the PvRbohB-RNAi roots. CONCLUSIONS: Our research provides substantial insights into the genetic interaction networks in the early stages of rhizobia and AM symbioses with P. vulgaris, as well as the differential roles that RbohB plays in processes related to ROS scavenging, cell wall remodeling, and phytohormone homeostasis during nodulation and mycorrhization in this legume.

Earthworms and mycorrhization increase copper phytoextraction by Canavalia ensiformis in sandy soil.

Phytoremediation is an alternative for remediating soil contamination by copper, and its efficiency has been shown to increase when arbuscular mycorrhizal fungi (AMF) and earthworms are separately inoculated into the soil. This study evaluated the isolated and combined effects of inoculating earthworms and arbuscular mycorrhizal fungi into a sandy soil on copper phytoremediation by Canavalia ensiformis. The plants were grown in a greenhouse in soil contaminated with 100 mg Cu kg-1 with and without being inoculated with the arbuscular mycorrhizal fungus Rhizoglomus clarum and the earthworm Eisenia andrei. The availabilities of solid-phase Cu and other nutrients in the soil solution and plant growth were evaluated along with Cu phytotoxicity based on photochemical efficiency and oxidative stress enzyme activity. Accumulation of Cu and other nutrients in the shoots and roots; mycorrhizal colonization, nodulation, and reproduction; and Cu accumulation in the earthworm tissues were also evaluated. The copper caused photosynthetic and biochemical damage that reduced the shoot dry weight by 44% and the root dry weight by 29%. However, the arbuscular mycorrhizal fungus alleviated the Cu toxicity to the plant and increased the shoot dry weight by 81% in the contaminated soil. The earthworms increased the Cu uptake and translocation to the shoot by 31%. The combined presence of the arbuscular mycorrhizal fungus and earthworms in the contaminated soil increased the growth and Cu content of the aerial plant tissues, yielding a 200% increase in Cu accumulation (metal content × biomass) in the C. ensiformis shoots. Combined inoculation with earthworms and arbuscular mycorrhizal fungi increased copper phytoextraction by Canavalia ensiformis in a sandy soil.

[Nutrient transfer and growth of Pinus greggii Engelm. inoculated with edible ectomycorrhizal mushrooms in two substrates]. / Transferencia de nutrientes y crecimiento de Pinus greggii Engelm. inoculado con hongos comestibles ectomicorrícicos en dos sustratos.

An ectomycorrhiza is a mutualistic symbiosis of paramount importance in forestry and tree production. One of the selection criteria of ectomycorrhizal fungi that has currently gained importance is their edibility due to the economic, ecological and cultural relevance of edible ectomycorrhizal mushrooms as a non-timber forest product. The effect of the inoculation with three edible ectomycorrhizal mushrooms: Laccaria laccata, Laccaria bicolor y Hebeloma leucosarx, which are widely sold in Mexico, on the growth and nutrient contents of Pinus greggii grown in an experimental substrate and a commercial substrate enriched with a slow-release fertilizer, was evaluated. Two years after sowing, differences in terms of shoot and root biomass and macro and micronutrient contents between inoculated and non-inoculated plants, were recorded independently of the fungal species and the substrate. Despite the fact that plants grown in the commercial substrate had higher growth and nutrient contents, their ectomycorrhizal colonization percentages were smaller than those of the plants grown in the experimental substrate. The differences in the nutrient transfer to the inoculated plant shoots among the evaluated fungal species were recorded. Ca mobilization by L. laccata, Na by L. bicolor and Mn by H. leucosarx were observed in the plants growing in the experimental substrate. It has been demonstrated that the selection of substrates constitutes an important factor in the production of ectomycorrhizal plants and that the three evaluated species of edible ectomycorrhizal mushrooms have an enormous potential in the controlled mycorrhization of P. greggii.

Transferencia de nutrientes y crecimiento de Pinus greggii Engelm. inoculado con hongos comestibles ectomicorrícicos en dos sustratos / Nutrient transfer and growth of Pinus greggii Engelm. inoculated with edible ectomycorrhizal mushrooms in two substrates

La ectomicorriza es una simbiosis mutualista de enorme importancia en la producción de árboles de valor forestal. Uno de los criterios de selección de hongos ectomicorrícicos de gran interés es su comestibilidad, por la importancia económica, ecológica y cultural de los hongos comestibles ectomicorrícicos como un producto forestal no maderable. En este estudio se evaluó el efecto de la inoculación con los hongos comestibles ectomicorrícicos, Laccaria laccata, Laccaria bicolor y Hebeloma leucosarx, en el crecimiento y el contenido nutricional de Pinus greggii, crecido en un sustrato experimental, o en un sustrato comercial enriquecido con un fertilizante de liberación lenta. Dos años después de la siembra, se observaron diferencias en el crecimiento aéreo y radical y en el contenido de macro- y micronutrientes entre plantas inoculadas y no inoculadas, independientemente de la especie fúngica y del sustrato utilizado. Las plantas crecidas en el sustrato comercial tuvieron mayor crecimiento y contenido de nutrientes; sin embargo, sus porcentajes de colonización fueron menores que los de plantas crecidas en el sustrato experimental. Existieron diferencias en la transferencia de nutrientes a la parte aérea de las plantas inoculadas, al comparar entre las especies fúngicas implicadas. Se observó transferencia de Ca por L. laccata, de Na por L. bicolor y de Mn por H.leucosarx en el sustrato experimental. La selección de sustratos constituye un factor clave en la producción de plantas ectomicorrizadas y las tres especies de hongos comestibles ectomicorrícicos evaluados tienen un potencial relevante para la micorrización controlada de P. greggii.

An ectomycorrhiza is a mutualistic symbiosis of paramount importance in forestry and tree production. One of the selection criteria of ectomycorrhizal fungi that has currently gained importance is their edibility due to the economic, ecological and cultural relevance of edible ectomycorrhizal mushrooms as a non-timber forest product. The effect of the inoculation with three edible ectomycorrhizal mushrooms: Laccaria laccata, Laccaria bicolor y Hebeloma leucosarx, which are widely sold in Mexico, on the growth and nutrient contents of Pinus greggii grown in an experimental substrate and a commercial substrate enriched with a slow-release fertilizer, was evaluated. Two years after sowing, differences in terms of shoot and root biomass and macro and micronutrient contents between inoculated and non-inoculated plants, were recorded independently of the fungal species and the substrate. Despite the fact that plants grown in the commercial substrate had higher growth and nutrient contents, their ectomycorrhizal colonization percentages were smaller than those of the plants grown in the experimental substrate. The differences in the nutrient transfer to the inoculated plant shoots among the evaluated fungal species were recorded. Ca mobilization by L. laccata, Na by L. bicolor and Mn by H. leucosarx were observed in the plants growing in the experimental substrate. It has been demonstrated that the selection of substrates constitutes an important factor in the production of ectomycorrhizal plants and that the three evaluated species of edible ectomycorrhizal mushrooms have an enormous potential in the controlled mycorrhization of P. greggii.

In vitro Scleroderma laeve and Eucalyptus grandis mycorrhization and analysis of atp6, 17S rDNA, and ras gene expression during ectomycorrhizal formation.

The interaction between fungi and plants that form ectomycorrhizae (ECM) promotes alterations in the gene expression profiles of both organisms. Fungal genes expression related to metabolism were evaluated at the pre-symbiotic stage and during the ECM development between Scleroderma laeve and Eucalyptus grandis. Partial sequences of ATP synthase (atp6), translation elongation factor (ef1α), the RAS protein (ras), and the 17S rDNA genes were isolated. The expression of the atp6 and 17S rDNA genes during the pre-symbiotic stage showed an approximately threefold increase compared to the control. During ECM development, the expression of the 17S rDNA gene showed a 4.4-fold increase after 3 days of contact, while the expression of the atp6 gene increased 7.23-fold by the 15th day, suggesting that protein synthesis and respiratory chain activities are increased during the formation of the mantle and the Hartig net. The ras gene transcripts were only detected by RT-PCR 30 days after fungus-plant contact, suggesting that RAS-mediated signal transduction pathways are functional during the establishment of symbiosis. The present study demonstrates that alterations in gene expression occur in response to stimuli released by the plant during ECM association and increases the understanding of the association between S. laeve and E. grandis.

Desempenho fotossintético e micorrização em plantas de soja Roundup Ready tratadas com diferentes formulações de glyphosate / Photosynthetic performance and mycorrhization in Roundup Ready soybean plants treated with different formulations of glyphosate

Com a expansão do cultivo de soja resistente ao glyphosate, observa-se aumento considerável tanto do uso desse herbicida como do número de formulações comerciais à base deste princípio ativo. Objetivou-se, portanto, avaliar o efeito de seis formulações de glyphosate (Roundup Original®, Trop®, Roundup Ultra®, Roundup WG®, Roundup Transorb R® e Zapp Qi®) em parâmetros fotossintéticos, colonização micorrízica e produtividade de soja (TMG 125 Roundup Ready), na região do Alto Paranaíba. Utilizou-se do delineamento em blocos casualizados, com quatro repetições. Uma única aplicação dos herbicidas (720 g e.a. ha-1) foi realizada entre os estádios V2-V3. Aos 3 e 7 dias após a aplicação dos tratamentos (DAT), foram feitas avaliações instantâneas de trocas gasosas entre 08:00 e 9:00 h, em folíolos completamente expandidos. Em seguida, o desempenho fotossintético foi avaliado por meio de curvas de luz (taxa de assimilação líquida de CO2 vs irradiância). A colonização micorrízica, altura de plantas e massa seca da parte aérea foram avaliadas quando as plantas de soja atingiram o estádio R2. Além disso, avaliaram-se o peso de sementes e produtividade de soja. As diferentes formulações de glyphosate não afetaram as trocas gasosas das plantas de soja, nem a eficiência dessas plantas na utilização da irradiância, razão pela qual também não se observou diferenças significativas na massa seca da parte aérea, colonização micorrízica e produtividade de soja.

The expansion of soybean resistant to glyphosate has caused considerable increase in the use of this herbicide as well as the number of formulations based on this active ingredient. The aim is evaluate the effect of six formulations of glyphosate (Roundup Original®, Trop®, Roundup Ultra®, Roundup WG®, Roundup Transorb R® e Zapp Qi®) in photosynthetic parameters, mycorrhizal colonization and soybean yield (TMG 125 Roundup Ready), in the Alto Paranaíba. It was used a randomized block design with four replications. A single application of herbicides (780 g a.e ha-1) was performed between stages V2-V3. At 3 and 7 days after application of the treatments were evaluated instantaneous gas exchange between 08:00 and 9:00 am, in fully expanded leaflets. Then, the photosynthetic performance was evaluated by means of light curves (CO2 assimilation rate vs. irradiance). The mycorrhizal colonization, plant height and shoot dry matter were assessed when the soybean plants reached the stage R2. In addition, we evaluated the weight of seeds and soybean yield. The different formulations of glyphosate did not affect gas exchange of soybean plants and the efficiency of these plants in the use of irradiance, therefore also no observed significant differences in shoot dry weight, mycorrhizal colonization and soybean yield.

Evaluación de un sistema para la micorrización in vitro en plantas demora de castilla (Rubus glaucus, Benth) / Evaluation of an in vitro mycorrhization system of blackberry plants (Rubus glaucus, Benth) / Avaliação de um sistema para micorrização in vitro em plantas de amora-preta (Rubus glaucus, Benth)

Objetivo. Obtener un sistema de micorrización in vitro en sistemas de cultivo autotrófico para plantas de mora de castilla (Rubusglaucus, Benth). Materiales y métodos. Se utilizaron esporas y fragmentos de raíces con vesículas del Hongo Formador de MicorrizaArbuscular (HFMA) Glomus sp. (GEV02). Se estableció un sistema de cultivo autotrófico para plántulas de mora, comparando dosmétodos de inoculación directa con el HFMA. Se cuantificó el número de esporas producidas, la longitud del micelio extraradical; asícomo el porcentaje de colonización del HFMA. Adicionalmente se midió la longitud aérea y radical, el peso fresco y seco de la partefoliar y radical para determinar el desarrollo de las plantas. Resultados. El sistema de cultivo autotrófico fue exitoso para plantas demora de castilla (Rubus glaucus, Benth); observándose un óptimo crecimiento de la parte aérea y radical de la planta. Adicionalmenteen este estudio se pudo obtener un sistema que permitió el desarrollo de Glomus sp (GEV02) bajo condiciones in vitro, con formaciónde estructuras típicas de la simbiosis como una buena colonización intraradical, con producción de arbúsculos y vesículas, así comoel desarrollo de micelio extraradical con hifas ramificadas y la formación de nuevas esporas. Conclusión. Las plantas de moramicropropagadas se asociaron con éxito, por primera vez, con un hongo formador de micorriza arbuscular bajo condiciones in vitro,permitiendo el desarrollo del sistema simbiótico HFMA Glomus sp., asociado a las raíces de plántulas de mora castilla micropropagadas...

Objective. Obtain an in vitromycorrhization system in autotrophic culture systems of blackberry plants (Rubus glaucus, Benth). Materials and methods. We usedspores and root fragments with vesicles of Arbuscular Mycorrhizal Fungus (AMF) Glomus sp (GEV02). We established an autotrophicculture system of blackberry plantlets comparing two methods of direct inoculation of the AMF. We measured the number of sporesproduced, the length of the extraradical mycelium as well as the percentage of colonization of the AMF. Additionally, we measuredthe shoot and root length, and the fresh and dry weight of the leaf and root parts to determine the plant development. Results. Theautotrophic culture system was successful for blackberry plants (Rubus glaucus, Benth; an optimal shoot and root growth was observed.Additionally, we obtained a system that allowed the development of Glomus sp. in in vitro conditions, with the formation of structurestypical of the symbiosis as well as a good intraradical colonization, with the production of arbuscules and vesicles, development ofextraradical mycelium with branched hyphae, and formation of new spores. Conclusion. For the first time, micropropagated blackberryplants associated successfully with an AMF under in vitro conditions, enabling the development of the symbiotic system AMF Glomussp. associated to roots of micropropagated blackberry plantlets...

Objetivo. Obter umsistema de micorrização in vitro em sistemas de cultura autotróficos para plantas de amora-preta (Rubus glaucus, Benth). Materiais emétodos. Foram usados esporos e fragmentos de raízes com vesículas do Fungo Formador Micorrízico Arbuscular (FFMA) Glomus sp.(GEV02). Foi estabelecido um sistema de cultivo autotrófico para mudas de amora-preta, comparando dois métodos de inoculação diretacom o FFMA. Foi quantificado o número de esporos produzidos, o comprimento do micélio extra radicular; bem como a porcentagemde colonização do FFMA. Além disso, foi medido o comprimento e o peso fresco e seco da parte folhar e radicular para determinar odesenvolvimento das plantas. Resultados. O sistema de cultivo autotrófico foi bem-sucedido para as plantas de amora-preta (Rubusglaucus, Benth), onde foi observado um crescimento ótimo da parte aérea e da raidicular da planta. Além disso, neste estudo foi obtido umsistema que permitiu o desenvolvimento de Glomus sp (GEV02) sob condições in vitro, com formação de estruturas típicas da simbiosecomo uma boa colonização intra radicular, com produção de arbúsculos e vesículas, assim como o desenvolvimento de micélio extraradicular com hifas ramificada e a formação de novos esporos. Conclusão. As plantas de amora-preta micropropagadas associaram-secom sucesso, pela primeira vez, com um fungo formador micorrízico arbuscular em condições in vitro, permitindo o desenvolvimentodo sistema simbiótico FFMA Glomus sp., associado às raízes das plântulas de amora-preta micropropagadas...

The role of mycorrhization helper bacteria in the establishment and action of ectomycorrhizae associations

More than 95 percent short roots of most terrestrial plants are colonized by mycorrhizal fungi as soon as they emerge in the upper soil profiles. The establishment of mycorrhizal association involves profound morphological and physiological changes in root and fungus. It is affected by other rhizospheric microorganisms, specifically by the bacteria. Bacteria may have developed mechanisms of selective interaction with surrounding microorganisms, with neutral or positive effects on mycorrhizal associations, but negative effect on root pathogens in general. Because of the beneficial effect of bacteria on mycorrhizae, the concept of Mycorrhization Helper Bacteria (MHB) was created. Five main actions of MHB on mycorrhizae were proposed: in the receptivity of root to the mycobiont, in root-fungus recognition, in fungal growth, in the modification of rhizospheric soil and in the germination of fungal propagules. MHB appear to develop a gradation of specificity for the mycobiont, but little or no specificity for the host plant in symbiosis. One of the main groups of MHB is the fluorescent Pseudomonas, well represented in diversity and cell density studies of mycorrhizal associations. This review covers the activity of MHB in the establishment of ectomycorrhizae, taking as model the effects of Pseudomonas sp. described in scientific literature.

The role of mycorrhization helper bacteria in the establishment and action of ectomycorrhizae associations.

More than 95 % short roots of most terrestrial plants are colonized by mycorrhizal fungi as soon as they emerge in the upper soil profiles. The establishment of mycorrhizal association involves profound morphological and physiological changes in root and fungus. It is affected by other rhizospheric microorganisms, specifically by the bacteria. Bacteria may have developed mechanisms of selective interaction with surrounding microorganisms, with neutral or positive effects on mycorrhizal associations, but negative effect on root pathogens in general. Because of the beneficial effect of bacteria on mycorrhizae, the concept of Mycorrhization Helper Bacteria (MHB) was created. Five main actions of MHB on mycorrhizae were proposed: in the receptivity of root to the mycobiont, in root-fungus recognition, in fungal growth, in the modification of rhizospheric soil and in the germination of fungal propagules. MHB appear to develop a gradation of specificity for the mycobiont, but little or no specificity for the host plant in symbiosis. One of the main groups of MHB is the fluorescent Pseudomonas, well represented in diversity and cell density studies of mycorrhizal associations. This review covers the activity of MHB in the establishment of ectomycorrhizae, taking as model the effects of Pseudomonas sp. described in scientific literature.

The role of mycorrhization helper bacteria in the establishment and action of ectomycorrhizae associations

More than 95 % short roots of most terrestrial plants are colonized by mycorrhizal fungi as soon as they emerge in the upper soil profiles. The establishment of mycorrhizal association involves profound morphological and physiological changes in root and fungus. It is affected by other rhizospheric microorganisms, specifically by the bacteria. Bacteria may have developed mechanisms of selective interaction with surrounding microorganisms, with neutral or positive effects on mycorrhizal associations, but negative effect on root pathogens in general. Because of the beneficial effect of bacteria on mycorrhizae, the concept of Mycorrhization Helper Bacteria (MHB) was created. Five main actions of MHB on mycorrhizae were proposed: in the receptivity of root to the mycobiont, in root-fungus recognition, in fungal growth, in the modification of rhizospheric soil and in the germination of fungal propagules. MHB appear to develop a gradation of specificity for the mycobiont, but little or no specificity for the host plant in symbiosis. One of the main groups of MHB is the fluorescent Pseudomonas, well represented in diversity and cell density studies of mycorrhizal associations. This review covers the activity of MHB in the establishment of ectomycorrhizae, taking as model the effects of Pseudomonas sp. described in scientific literature.

Efecto de la incculación con hongos formadores e micorrizas arbusculares sobree plántulas de caucho / Effects Of Inoculation With Arbuscular Mycorrhizal Fungi On Rubber Seedlings

Hongos formadores de micorrizas arbusculares (HFMA) obtenidos a partir de suelos caucheros se multiplicaron en plantas de Lolium sp., con 73% de colonización radical luego de cuatro meses. Se obtuvieron siete morfotipos de HFMA, con los cuales se inocularon dos grupos de plántulas de Hevea brasiliensis: 1) producidas in vivo a partir de semilla; 2) producidas in vitro por rescate de embrión, para determinar efectos sobre mortalidad, crecimiento, micorrización y contenido de fósforo foliar. Los niveles de colonización por HFMA para las plántulas obtenidas in vitro e in vivo fueron de 12,6% y de 44,7%, respectivamente. La biomasa media total acumulada por las plántulas producidas in vitro fue de 0,41 y de 1,40 g por las procedentes del material in vivo, en comparación con los controles no inoculados, los cuales acumularon 0,37 y 0,40 g , respectivamente. El tratamiento con HFMA disminuyó la mortalidad en las plántulas obtenidas in vitro, aunque no tuvo un efecto significativo sobre el contenido de fósforo foliar. La respuesta del crecimiento de las plántulas inoculadas fue diferente dependiendo del origen del material vegetal y del tipo de inóculo (nativo o no nativo). La simbiosis entre HFMA y H. brasiliensis se desarrolló en condiciones controladas de crecimiento, aunque su avance dependió del estado de desarrollo de la plántula. No obstante, influyó en el crecimiento y en la disminución de la mortalidad de las plántulas, lo que abre la posibilidad de utilizarla como alternativa de inoculación en las fases tempranas de obtención del material vegetal.

Hevea brasiliensis rubber plants were inoculated with native arbuscular mycorrhizal fungi (AMF) during their greenhouse acclimatization. The AMF were multiplied for 4 months associated with Lolium sp. plants having 73% root colonization. Seven morphotypes were obtained. Two different groups of H. brasiliensis plants were inoculated with these morphotypes to determine AMF effect on mortality rate, growth, mycorrhization and leaf P content: those produced in vivo by seed germination and those produced in vitro by micropropagation. Plantlets produced in vitro returned 12.6% AMF colonization and 0.41 g accumulated dry biomass, whereas seedlings produced in vivo had 44.7% and 1.40 g , respectively, compared to control plants with no AMF inoculation which accumulated 0.37 g (in vitro) and 0.40 g (in vivo). AMF inoculation reduced the plants’ mortality rate regarding in vitro produced material; however, it did not influence foliar P content. Inoculated plants’ growth response was different, depending on plant material and the kind of inoculum used (native or foreign). Symbiosis developed between AMF and H. brasiliensis in controlled growth conditions although its advance was limited by the plants’ growth stage. Nevertheless, such association influenced inoculated plants’ biomass accumulation and decreased their mortality rate and could be used as an alternative treatment during the earliest stages of H. brasiliensis plantlet production.