Global patterns of plant root colonization intensity by mycorrhizal fungi explained by climate and soil chemistry

Aim Most vascular plants on Earth form mycorrhizae, a symbiotic relationship between plants and fungi. Despite the broad recognition of the importance of mycorrhizae for global carbon and nutrient cycling, we do not know how soil and climate variables relate to the intensity of colonization of plant roots by mycorrhizal fungi. Here we quantify the global patterns of these relationships. Location Global. Methods Data on plant root colonization intensities by the two dominant types of mycorrhizal fungi world-wide, arbuscular (4887 plant species in 233 sites) and ectomycorrhizal fungi (125 plant species in 92 sites), were compiled from published studies. Data for climatic and soil factors were extracted from global datasets. For a given mycorrhizal type, we calculated at each site the mean root colonization intensity by mycorrhizal fungi across all potentially mycorrhizal plant species found at the site, and subjected these data to generalized additive model regression analysis with environmental factors as predictor variables. Results We show for the first time that at the global scale the intensity of plant root colonization by arbuscular mycorrhizal fungi strongly relates to warm-season temperature, frost periods and soil carbon-to-nitrogen ratio, and is highest at sites featuring continental climates with mild summers and a high availability of soil nitrogen. In contrast, the intensity of ectomycorrhizal infection in plant roots is related to soil acidity, soil carbon-to-nitrogen ratio and seasonality of precipitation, and is highest at sites with acidic soils and relatively constant precipitation levels. Main conclusions We provide the first quantitative global maps of intensity of mycorrhizal colonization based on environmental drivers, and suggest that environmental changes will affect distinct types of mycorrhizae differently. Future analyses of the potential effects of environmental change on global carbon and nutrient cycling via mycorrhizal pathways will need to take into account the relationships discovered in this study.

A site-specific recombinase is required for competitive root colonization by Pseudomonas fluorescens WCS365

A colonization mutant of the efficient root-colonizing biocontrol strain Pseudomonas fluorescens WCS365 is described that is impaired in competitive root-tip colonization of gnotobiotically grown potato, radish, wheat, and tomato, indicating a broad host range mutation. The colonization of the mutant is also impaired when studied in potting soil, suggesting that the defective gene also plays a role under more natural conditions. A DNA fragment that is able to complement the mutation for colonization revealed a multicistronic transcription unit composed of at least six ORFs with similarity to lppL, lysA, dapF, orf235/233, xerC/sss, and the largely incomplete orf238. The transposon insertion in PCL1233 appeared to be present in the orf235/233 homologue, designated orf240. Introduction of a mutation in the xerC/sss homologue revealed that the xerC/sss gene homologue rather than orf240 is crucial for colonization. xerC in Escherichia coli and sss in Pseudomonas aeruginosa encode proteins that belong to the λ integrase family of site-specific recombinases, which play a role in phase variation caused by DNA rearrangements. The function of the xerC/sss homologue in colonization is discussed in terms of genetic rearrangements involved in the generation of different phenotypes, thereby allowing a bacterial population to occupy various habitats. Mutant PCL1233 is assumed to be locked in a phenotype that is not well suited to compete for colonization in the rhizosphere. Thus we show the importance of phase variation in microbe–plant interactions.

Endophytic colonization of barley (Hordeum vulgare) roots by the nematophagous fungus Pochonia chlamydosporia reveals plant growth promotion and a general defense and stress transcriptomic response

Plant crop yields are negatively conditioned by a large set of biotic and abiotic factors. An alternative to mitigate these adverse effects is the use of fungal biological control agents and endophytes. The egg-parasitic fungus Pochonia chlamydosporia has been traditionally studied because of its potential as a biological control agent of plant-parasitic nematodes. This fungus can also act as an endophyte in monocot and dicot plants, and has been shown to promote plant growth in different agronomic crops. An Affymetrix 22K Barley GeneChip was used in this work to analyze the barley root transcriptomic response to P. chlamydosporia root colonization. Functional gene ontology (GO) and gene set enrichment analyses showed that genes involved in stress response were enriched in the barley transcriptome under endophytism. An 87.5 % of the probesets identified within the abiotic stress response group encoded heat shock proteins. Additionally, we found in our transcriptomic analysis an up-regulation of genes implicated in the biosynthesis of plant hormones, such as auxin, ethylene and jasmonic acid. Along with these, we detected induction of brassinosteroid insensitive 1-associated receptor kinase 1 (BR1) and other genes related to effector-triggered immunity (ETI) and pattern-triggered immunity (PTI). Our study supports at the molecular level the growth-promoting effect observed in plants endophytically colonized by P. chlamydosporia, which opens the door to further studies addressing the capacity of this fungus to mitigate the negative effects of biotic and abiotic factors on plant crops.

Influence of metalaxyl on Glomus fasciculatum associated with wheat (Triticum aestivum L)

Soil incorporation of metalaxyl [methyl N-(2-methoxyacetyl)-N-(2,6,xylyl)-DL-alaninate] significantly enhanced root colonization of the vesicular-arbuscular (VA) mycorrhizal fungi Glomus fasciculatum associated with wheat. The stimulatory response of VA mycorrhizal fungi to low concentration of metalaxyl resulted in increased plant biomass production, nutrient uptake and grain yield of wheat. However, higher concentrations of metalaxyl, particularly 2.5 ppm of metalaxyl affected the mycorrhizal infection and seed yield of wheat, Addition of urban compost to an extent ameliorated the toxic effect of fungicide on VA mycorrhizal colonization, plant growth and yield of wheat when compared to unamended soil.

Manejo da micorriza arbuscular por meio da rotação de culturas nos sistemas agrícolas do Cerrado.

2001

Arbuscular mycorrhizal fungi and collembola non-additively increase soil aggregation

Soil aggregation is a principal ecosystem process mediated by soil biota. Collembola and arbuscular mycorrhizal (AM) fungi are important groups in the soil, and can interact in various ways. Few studies have examined collembola effects on soil aggregation, while many have quantified AM effects. Here, we asked if collembola have any effect on soil aggregation, and if they alter AM fungi-mediated effects on soil aggregation.

We carried out a factorial greenhouse study, manipulating the presence of both collembola and AM fungi, using two different plant species, Sorghum vulgare and Daucus carota. We measured root length and biomass, AMF (and non-AMF) soil hyphal length, root colonization, and collembolan populations, and quantified water stable soil aggregates (WSA) in four size classes.

Soil exposed to growth of AMF hyphae and collembola individually had higher WSA than control treatments. Moreover, the interaction effects between AMF and collembola were significant, with nonadditive increases in the combined application compared to the single treatments.

Our findings show that collembola can play a crucial role in maintaining ecological sustainability through promoting soil aggregation, and point to the importance of considering organism interactions in understanding formation of soil structure. (C) 2011 Elsevier Ltd. All rights reserved.

Evolução da população do fungo nematófago Pochonia chlamydosporia -isolado PcMR, após inoculação, no solo e na raiz do tomateiro cultivado em estufa

O fungo Pochonia chlamydospoia é um potencial agente de controlo biológico dos nemátodes-das-galhas-radiculares. Com este trabalho, pretendeu-se avaliar a eficácia de inoculações de clamidósporos no solo, no estabelecimento de uma população do fungo no solo e na raiz de tomateiro em estufa com níveis de densidade iguais ou superiores aos considerados como necessários para um eficaz controlo dos nematodes-das-galhas-radiculares. Ao longo de dois anos de ensaio, fórum efetuadas inoculações do isolado PcMR e avaliada a densidade de fungo no solo e na raiz, As inoculações efetuadas permitiram estabelecer uma população de P. chlamydosporia no solo e atingir os valores de densidade pretendidos. No entanto, os valores pretendidos para colonização da raiz pelo fungo foram atingidos apenas no primeiro ano. Foi igualmente demonstrada a capacidade do fungo em se manter no solo durante longos períodos de tempo mesmo na ausência de cultura e em condições adversas de humidade e temperatura. /ABSTRACT: Pochonia chlamydosporia is a potential root-knot nematode biological control agent. The aim of this work was to evaluate the effectiveness of chlamydospore inoculations at the soil, for the establishment at both soil and greenhouse tomato root, of a fungus population in density levels equal or superior to those considered as needed for an effective control of root-knot nematode. Along two years, several inoculations using the Portuguese isolate PcMR were made and the density of fungus at the soil and roots studied. These inoculations allowed the establishment of a population of P. chlamydosporia at the soil and achieve the desired density values. However, only in the first year of assay, the desired values of root colonization by fungus were achieved. lt was also demonstrated that P. chlamydosporia can survive for itself at the soil for a long period of time even in the absence of plant culture and in adverse moist and temperature conditions.

Starvation Induces Expression of the Plant-Adhesin Gene, Mad2, of the Entomopathogenic Fungus Metarhizium robertsii.

Metarhizium robertsii is an entomopathogenic fungus that is additionally plant rhizosphere competent. Two adhesin-encoding gens, Mad1 and Mad2, are involved in insect pathogenesis or plant root colonization, respectively. This study examined differential expression of the Mad genes for M robertsii grown on a variety of insectand plant-related substrates. Mad1 was up regulated in response to insect cuticles and up regulation of Mad2 resulted from root exudates, tomato stems and non-preferred carbohydrates. A time course analysis that compared water, minimal media, and nutrient rich broth revealed Mad2 gene expression increased as nutrient availability decreased. The regulation of Mad2 compared to known stress-related genes (Hsp30, Hsp70 and ssgA) under various stresses (nutrient, pH, osmotic, oxidative, temperature) revealed Mad2 to be generally up regulated by nutrient starvation only. Examination of the Mad2 promoter region revealed two copies of a stress-response element (S TRE) known to be regulated under the general stress response pathway.

Diversité des champignons endophytes mycorhiziens et de classe II chez le pois chiche, et influence du génotype de la plante

réalisé en cotutelle avec la Faculté des Sciences de Tunis, Université Tunis El Manar.

Development and Integration of Biocontrol Products in Branched Broomrape (Phelipanche ramosa) management in Tomato

Parasitic weeds of the genera Striga, Orobanche, and Phelipanche pose a severe problem for agriculture because they are difficult to control and are highly destructive to several crops. The present work was carried out during the period October, 2009 to February, 2012 to evaluate the potential of arbuscular mycorrhizal fungi (AMF) to suppress P. ramosa on tomatoes and to investigate the effects of air-dried powder and aqueous extracts from Euphorbia hirta on germination and haustorium initiation in Phelipanche ramosa. The work was divided into three parts: a survey of the indigenous mycorrhizal flora in Sudan, second, laboratory and greenhouse experiments (conducted in Germany and Sudan) to construct a base for the third part, which was a field trial in Sudan. A survey was performed in 2009 in the White Nile state, Sudan to assess AMF spore densities and root colonization in nine fields planted with 13 different important agricultural crops. In addition, an attempt was made to study the relationship between soil physico-chemical properties and AMF spore density, colonization rate, species richness and other diversity indices. The mean percentage of AMF colonization was 34%, ranging from 19-50%. The spore densities (expressed as per 100 g dry soil) retrieved from the rhizosphere of different crops were relatively high, varying from 344 to 1222 with a mean of 798. There was no correlation between spore densities in soil and root colonization percentage. A total of 45 morphologically classifiable species representing ten genera of AMF were detected with no correlation between the number of species found in a soil sample and the spore density. The most abundant genus was Glomus (20 species). The AMF diversity expressed by the Shannon–Weaver index was highest in sorghum (H\= 2.27) and Jews mallow (H\= 2.13) and lowest in alfalfa (H\= 1.4). With respect to crop species, the genera Glomus and Entrophospora were encountered in almost all crops, except for Entrophospora in alfalfa. Kuklospora was found only in sugarcane and sorghum. The genus Ambispora was recovered only in mint and okra, while mint and onion were the only species on which no Acaulospora was found. The hierarchical cluster analysis based on the similarity among AMF communities with respect to crop species overall showed that species compositions were relatively similar with the highest dissimilarity of about 25% separating three of the mango samples and the four sorghum samples from all other samples. Laboratory experiments studied the influence of root and stem exudates of three tomato varieties infected by three different Glomus species on germination of P. ramosa. Root exudates were collected 21or 42 days after transplanting (DAT) and stem exudates 42 DAT and tested for their effects on germination of P. ramosa seeds in vitro. The tomato varieties studied did not have an effect on either mycorrhizal colonization or Phelipanche germination. Germination in response to exudates from 42 day old mycorrhizal plants was significantly reduced in comparison to non-mycorrhizal controls. Germination of P. ramosa in response to root exudates from 21 day old plants was consistently higher than for 42 day-old plants (F=121.6; P<.0001). Stem diffusates from non-mycorrhizal plants invariably elicited higher germination than diffusates from the corresponding mycorrhizal ones and differences were mostly statistically significant. A series of laboratory experiments was undertaken to investigate the effects of aqueous extracts from Euphorbia hirta on germination, radicle elongation, and haustorium initiation in P. ramosa. P. ramosa seeds conditioned in water and subsequently treated with diluted E. hirta extract (10-25% v/v) displayed considerable germination (47-62%). Increasing extract concentration to 50% or more reduced germination in response to the synthetic germination stimulants GR24 and Nijmegen-1 in a concentration dependent manner. P. ramosa germlings treated with diluted Euphorbia extract (10-75 % v/v) displayed haustorium initiation comparable to 2, 5-Dimethoxy-p-benzoquinon (DMBQ) at 20 µM. Euphorbia extract applied during conditioning reduced haustorium initiation in a concentration dependent manner. E. hirta extract or air-dried powder, applied to soil, induced considerable P. ramosa germination. Pot experiments were undertaken in a glasshouse at the University of Kassel, Germany, to investigate the effects of P. ramosa seed bank on tomato growth parameters. Different Phelipanche seed banks were established by mixing the parasite seeds (0 - 32 mg) with the potting medium in each pot. P. ramosa reduced all tomato growth parameters measured and the reduction progressively increased with seed bank. Root and total dry matter accumulation per tomato plant were most affected. P. ramosa emergence, number of tubercles, and tubercle dry weight increased with the seed bank and were, invariably, maximal with the highest seed bank. Another objective was to determine if different AM fungi differ in their effects on the colonization of tomatoes with P. ramosa and the performance of P. ramosa after colonization. Three AMF species viz. GIomus intraradices, Glomus mosseae and Glomus Sprint® were used in this study. For the infection, P. ramosa seeds (8 mg) were mixed with the top 5 cm soil in each pot. No mycorrhizal colonization was detected in un-inoculated control plants. P. ramosa infested, mycorrhiza inoculated tomato plants had significantly lower AMF colonization compared to plants not infested with P. ramosa. Inoculation with G. intraradices, G. mosseae and Glomus Sprint® reduced the number of emerged P. ramosa plants by 29.3, 45.3 and 62.7% and the number of tubercles by 22.2, 42 and 56.8%, respectively. Mycorrhizal root colonization was positively correlated with number of branches and total dry matter of tomatoes. Field experiments on tomato undertaken in 2010/12 were only partially successful because of insect infestations which resulted in the complete destruction of the second run of the experiment. The effects of the inoculation with AMF, the addition of 10 t ha-1 filter mud (FM), an organic residues from sugar processing and 36 or 72 kg N ha-1 on the infestation of tomatoes with P. ramosa were assessed. In un-inoculated control plants, AMF colonization ranged between 13.4 to 22.1% with no significant differences among FM and N treatments. Adding AMF or FM resulted in a significant increase of branching in the tomato plants with no additive effects. Dry weights were slightly increased through FM application when no N was applied and significantly at 36 kg N ha-1. There was no effect of FM on the time until the first Phelipanche emerged while AMF and N application interacted. Especially AMF inoculation resulted in a tendency to delayed P. ramosa emergence. The marketable yield was extremely low due to the strong fruit infestation with insects mainly whitefly Bemisia tabaci and tomato leaf miner (Tuta absoluta). Tomatoes inoculated with varied mycorrhiza species displayed different response to the insect infestation, as G. intraradices significantly reduced the infestation, while G. mosseae elicited higher insect infestation. The results of the present thesis indicate that there may be a potential of developing management strategies for P. ramosa targeting the pre-attachment stage namely germination and haustorial initiation using plant extracts. However, ways of practical use need to be developed. If such treatments can be combined with AMF inoculation also needs to be investigated. Overall, it will require a systematic approach to develop management tools that are easily applicable and affordable to Sudanese farmers. It is well-known that proper agronomical practices such as the design of an optimum crop rotation in cropping systems, reduced tillage, promotion of cover crops, the introduction of multi-microbial inoculants, and maintenance of proper phosphorus levels are advantageous if the mycorrhiza protection method is exploited against Phelipanche ramosa infestation. Without the knowledge about the biology of the parasitic weeds by the farmers and basic preventive measures such as hygiene and seed quality control no control strategy will be successful, however.

Contrasting arbuscular mycorrhizal communities colonizing different host plants show a similar response to a soil phosphorus concentration gradient

High soil phosphorus (P) concentration is frequently shown to reduce root colonization by arbuscular mycorrhizal (AM) fungi, but the influence of P on the diversity of colonizing AM fungi is uncertain. We used terminal restriction fragment length polymorphism (T-RFLP) of 18S rDNA and cloning to assess diversity of AM fungi colonizing maize (Zea mays), soybean (Glycene max) and field violet (Viola arvensis) at three time points in one season along a P gradient of 10280mgl1 in the field. Percentage AM colonization changed between sampling time points but was not reduced by high soil P except in maize. There was no significant difference in AM diversity between sampling time points. Diversity was reduced at concentrations of P > 25mgl1, particularly in maize and soybean. Both cloning and T-RFLP indicated differences between AM communities in the different host species. Host species was more important than soil P in determining the AM community, except at the highest P concentration. Our results show that the impact of soil P on the diversity of AM fungi colonizing plants was broadly similar, despite the fact that different plants contained different communities. However, subtle differences in the response of the AM community in each host were evident.

Local adaptation in migrated interior Douglas-fir seedlings is mediated by ectomycorrhizas and other soil factors

Separating edaphic impacts on tree distributions from those of climate and geography is notoriously difficult. Aboveground and belowground factors play important roles, and determining their relative contribution to tree success will greatly assist in refining predictive models and forestry strategies in a changing climate. In a common glasshouse, seedlings of interior Douglas-fir (Pseudotsuga menziesii var. glauca) from multiple populations were grown in multiple forest soils. Fungicide was applied to half of the seedlings to separate soil fungal and nonfungal impacts on seedling performance. Soils of varying geographic and climatic distance from seed origin were compared, using a transfer function approach. Seedling height and biomass were optimized following seed transfer into drier soils, whereas survival was optimized when elevation transfer was minimised. Fungicide application reduced ectomycorrhizal root colonization by c. 50%, with treated seedlings exhibiting greater survival but reduced biomass. Local adaptation of Douglas-fir populations to soils was mediated by soil fungi to some extent in 56% of soil origin by response variable combinations. Mediation by edaphic factors in general occurred in 81% of combinations. Soil biota, hitherto unaccounted for in climate models, interacts with biogeography to influence plant ranges in a changing climate.

Crescimento e micorrização de genótipos de milho em casa de vegetação

O trabalho foi desenvolvido em casa de vegetação com o objetivo de comparar o crescimento e a micorrização por fungos micorrízicos arbusculares (FMA) em nove genótipos de milho, além de verificar o potencial de inóculo de FMA do solo. Coletado de uma área de cerrado sensu stricto ocupada por pastagem degradada, o solo foi adubado, misturado com areia de rio, fumigado e colocado em sacos plásticos (3 kg). Foram semeadas cinco sementes de cada genótipo de milho em 20 sacos, mas apenas 10 receberam cerca de 300 esporos de FMA, coletados do solo de pastagem. Cada saco constituiu-se em uma repetição, com apenas uma planta. As avaliações de altura e diâmetro do caule foram realizadas aos 15, 30, 45 e 60 dias após a emergência, além de massa seca do sistema radicular (MSR) e parte aérea (MSPA), colonização micorrízica (COL) e dependência micorrízica (DM). Concomitantemente, um segundo experimento foi realizado para avaliar o potencial de inóculo de FMA do solo de pastagem, o qual passou por uma diluição seriada de 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% e 10%, incluindo apenas o solo não esterilizado (100%) e somente solo esterilizado (0%), em sacos plásticos, semeado o híbrido Tractor. Após 60 dias, as raízes foram colhidas para quantificar a colonização micorrízica. A inoculação de FMA acarretou incrementos na produção de matéria seca de forma diferenciada entre genótipos; com Condá, F0, D1 e F8 exibindo os maiores valores de MSPA, enquanto Tractor e D7 os menores valores de MSR. Os genótipos não responsivos ou pouco responsivos quanto à dependência micorrízica tiveram comportamento diferente quanto à COL, com Condá, Sol da Manhã, F0 e D1 proporcionando média de 60%. Verificou-se que a área de pastagem, mesmo degradada, propiciou alto potencial de inóculo, revelado pela alta porcentagem de colonização das raízes por FMA.

Glomus clarum e G. etunicatum: cultivo em solo e aeroponia

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Crescimento, fosfatase ácida e micorrização de espécies arbóreas, em solo de cerrado degradado

A ocupação do cerrado para aumentar a produção agrícola tem gerado a degradação do solo e uma prática recomendada na revegetação dessas áreas é a introdução de espécies arbóreas. O objetivo do trabalho foi avaliar o crescimento (altura e massa fresca e seca de parte aérea), a atividade da fosfatase ácida foliar e colonização micorrízica de mudas de espécies arbóreas não nativas em solo de cerrado degradado. O trabalho foi desenvolvido em casa de vegetação em Ilha Solteira, empregando solo proveniente de uma área de cerrado degradado em processo de regeneração natural, localizada no município de Três Lagoas (MS). O solo, misturado com areia de rio (4:1), foi fumigado com brometo de metila e distribuído em sacos plásticos (2,5 L). Para o tratamento com inoculação de FMA, 100 g de solo inóculo (solo de área de cerrado preservado) foi depositado na superfície, logo após o transplante das mudas. Pelos resultados, Psidium guajava L. e Croton floribundus Spreng, seguidos por Tabebuia chrysotricha (Mart. ex DC) Standl) e Rapanea ferruginea (Ruiz et Pav) Mez., tiveram alta colonização radicular e foram altamente ou muito responsivas à micorrização, sugerindo seu potencial em projetos de revegetação no cerrado brasileiro ou no enriquecimento de áreas degradadas.