RESUMEN
Pecan trees form a symbiotic relationship with ectomycorrhizal fungi (ECM), which actively provide nutrition to the roots and protect them from phytopathogens. Although these trees originated in the southern United States and northern Mexico, information on their root colonization by ECM is insufficient in terms of a representative number of samples, both in these regions and worldwide. Therefore, the objectives of this study were to determine the percentage of ectomycorrhizal colonization (ECM) of pecan trees of different ages in conventional and organic agronomic orchards and to identify ectomycorrhizal sporocarps, both morphologically and molecularly. The rhizospheric soil properties and the ECM percentages were analyzed for 14 Western variety pecan tree orchards between 3 and 48 years of age and grouped according to the agronomic management method. DNA extraction, internal transcribed spacer amplification, and sequencing were conducted on the fungal macroforms. The ECM colonization percentage fluctuated between 31.44 and 59.89%. Soils with low phosphorus content showed higher ECM colonization. The ECM concentrations were relatively homogeneous in relation to the ages of the trees, and organic matter content did not affect the percentage of ECM colonization. The highest ECM percentages occurred with the sandy clay crumb texture soil, with an average of 55% ECM, followed by sandy clay loam soils with 49.5%. The Pisolithus arenarius and Pisolithus tinctorius fungi were molecularly identified from sporocarps associated with pecan trees. This is the first study that reports Pisolithus arenarius as being associated with this tree.
RESUMEN
RESUMEN Los robledales en Colombia están dominados por la especie Quercus humboldtii Bonpl. Esta especie se encuentra en categoría de vulnerable debido a la deforestación para generar cultivos, zonas ganaderas y plantaciones de especies exóticas, ocasionando la formación de bordes por el deterioro del ecosistema. Estos bosques establecen asociaciones simbióticas con especies de hongos ectomicorrícicos, permitiendo el intercambio de nutrientes entre las hifas de los hongos y las raíces de las plantas. Este estudio analiza el efecto de borde en un área al interior (BNI-C) y al borde de un bosque de roble no intervenido (BNI-B), además de dos bordes de bosque con intervención antropogénica, una en contacto con plantación de Eucalyptus sp. (BE) y otro con ganadería (BG). Se estableció el borde de bosque mediante variables ambientales (temperatura ambiente, luminosidad temperatura y humedad del suelo). Se colectaron raicillas de siete árboles tanto de interior como de borde para medir la colonización y caracterizar morfológicamente las ectomicorrizas asociadas a las raíces de roble. Se evidenció el efecto de borde en el grado de colonización ectomicorrícica en las raíces de Q. humboldtii con porcentajes de 18 a 30 % en BNI, 15 % en BE y 47 % en BG. Los géneros ectomicorrícicos Cenococcum sp. y Lactarius sp. presentaron la mayor abundancia en los tres bosques, variando considerablemente cerca a los bordes en BG y BE. Se evidenciaron cambios de porcentaje de colonización y diversidad de morfotipos de ectomicorrizas en los bordes de los dos bosques intervenidos .
ABSTRACT The oak forests in Colombia are dominated by the species Quercus humboldtii Bonpl. which is in the vulnerable category due to deforestation to generate crops, livestock areas and plantations of exotic species, causing the formation of edges due to the deterioration of the ecosystem. These forests establish symbiotic associations with species of ectomycorrhizal fungi, allowing the exchange of nutrients and water between fungal hyphae and plant roots. This study analyzes the edge effect in the interior (BNI-C) and at the edge of an undisturbed oak forest (BNI-B), in addition to two forest edges with anthropogenic intervention, one in contact with a plantation of Eucalyptus sp. (BE) and another with cattle ranching (BG). The forest edge was established by measuring environmental variables (ambient temperature, luminosity, temperature, and soil humidity). Oak roots were collected from seven trees at the interior and edge of each forest and the quantification of colonization and morphological characterization of ectomycorrhizae was made. The edge effect was evidenced in the degree of ectomycorrhizal colonization in the roots of Q. humboldtii with percentages of 18 to 30 % in BNI, 15 % in BE and 47 % in BG. The ectomycorrhizal genera Cenococcum sp. and Lactarius sp. showed the highest abundance in the three forests, varying considerably near the edges in BG and BE. Changes in the percentage of colonization and morphotype diversity of ectomycorrhizae were evidenced at the forest edge in contact with the two disturbed areas.
RESUMEN
Arbuscular mycorrhiza (AM) and ectomycorrhiza (EcM) are the most abundant and widespread types of mycorrhizal symbiosis, but there is little and sometimes conflicting information regarding the interaction between AM fungi (AMF) and EcM fungi (EcMF) in soils. Their competition for resources can be particularly relevant in successional ecosystems, which usually present a transition from AM-forming herbaceous vegetation to EcM-forming woody species. The aims of this study were to describe the interaction between mycorrhizal fungal communities associated with AM and EcM hosts naturally coexisting during primary succession on spoil banks and to evaluate how this interaction affects growth and mycorrhizal colonization of seedlings of both species. We conducted a greenhouse microcosm experiment with Betula pendula and Hieracium caespitosum as EcM and AM hosts, respectively. They were cultivated in three-compartment rhizoboxes. Two lateral compartments contained different combinations of both host plants as sources of fungal mycelia colonizing the middle compartment, where fungal biomass, diversity, and community composition as well as the growth of each host plant species' seedlings were analyzed. The study's main finding was an asymmetric outcome of the interaction between the two plant species: while H. caespitosum and associated AMF reduced the abundance of EcMF in soil, modified the composition of EcMF communities, and also tended to decrease growth and mycorrhizal colonization of B. pendula seedlings, the EcM host did not have such effects on AM plants and associated AMF. In the context of primary succession, these findings suggest that ruderal AM hosts could hinder the development of EcM tree seedlings, thus slowing the transition from AM-dominated to EcM-dominated vegetation in early successional stages.
RESUMEN
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.
Asunto(s)
Basidiomycota/metabolismo , ADN Ribosómico/metabolismo , Eucalyptus/metabolismo , Proteínas Fúngicas/metabolismo , Genes Fúngicos , Genes ras , Micorrizas/metabolismo , Basidiomycota/genética , ADN Ribosómico/genética , Eucalyptus/genética , Proteínas Fúngicas/genética , Micorrizas/genética , Micorrizas/crecimiento & desarrollo , Transducción de SeñalRESUMEN
Craterellus olivaceoluteus sp. nov. and Craterellus cinereofimbriatus sp. nov. are described as new to science. These fungi were collected from Guyana in association with ectomycorrhizal host trees in the genera Dicymbe (Fabaceae subfam. Caesalpinioideae) and Pakaraimaea (Dipterocarpaceae). Cantharellus guyanensis Mont., originally described from French Guiana, is redescribed from recent collections from Guyana, with additional range extensions for the species provided based on material examined from French Guiana, Venezuela, and north central, northeastern and southern Brazil, circumscribing nearly the entire Guiana Shield region and beyond. A new distribution record from French Guiana is provided for Craterellus excelsus T.W. Henkel & Aime. Macromorphological, micromorphological and habitat data are provided for the new species and C. guyanensis as well as DNA sequence data from the nuclear ribosomal regions of the internal transcribed spacer (ITS) and 28S large subunit (LSU); additional sequence data is provided for C. guyanensis and C. excelsus specimens collected outside Guyana. The relationships of these taxa within the Cantharellaceae were evaluated with phylogenetic analyses of ITS and LSU sequence data. This work brings the total number of Cantharellaceae species known from Guyana to eight. A key to the Cantharellus and Craterellus species known from the lowland Neotropics and extralimital montane Central and South America is provided.