Arbuscular mycorrhizal fungi (AMF) have been hypothesized to enhance plant adaptation and growth in petroleum-contaminated soils. Nevertheless, neither AMF-biodiversity under chronically petroleum-contaminated soils nor spore germination response to petroleum hydrocarbons has been well studied. Chronically petroleum-contaminated rhizosphere soil and roots from Echinochloa polystachya, Citrus aurantifolia and C. aurantium were collected from Activo Cinco Presidentes, Tabasco, Mexico. Root colonization and spore abundance were evaluated. Additionally, rhizosphere soil samples were propagated using Sorghum vulgare L. as a plant trap under greenhouse conditions; subsequently, AMF-spores were identified. AMF-colonization ranged from 63 to 77% while spore number ranged from 715 to 912 in 100 g soil, suggesting that AMF tolerate the presence of petroleum hydrocarbons in the rhizosphere. From grass species, four AMF-morphospecies were identified: Glomus ambisporum, G. sinuosum (previously described as Sclerocystis sinuosum), Acaulospora laevis, and Ambispora gerdermanni. From citrus trees, four AMF-species were also identified: Scutellospora heterogama, G. ambisporum, Acaulospora scrobiculata, and G. citricola. In a second study, it was observed that spore germination and hyphal length of G. mosseae, G. ambisporum, and S. heterogama were significantly reduced by either volatile compounds of crude oil or increased concentrations of benzo[a ]pyrene or phenanthrene in water-agar.

The knowledge about the genetic and the functional diversity of Arbuscular Mycorrhizal Fungi (AMF) is an important ecological issue that deserves greater research efforts specially when trying to use them into biotechnological approaches in agriculture, horticulture, forestry and ecological restoration. Genetic diversity of AMF is almost unexplored in Mexico. In turn, the functional diversity of these fungi has been poorly evaluated from some ecological studies. However, based on the beneficial effects on growth promotion and nutrition of plants of agronomic importance, some promising strains and consortia of AMF have been obtained. This work shows the beneficial effects of AMF that were isolated from several regions of the Mexican Republic, and to highlight the need to explore the genetic and the functional diversity of AMF from different ecosystems and agrosystems of Mexico, which is considered not only as one of the most biodiverse countries but also for being a domestication center for several cultivated plants which are important from a cultural and a human nutrition point of view.

Background: Big-leaf mahogany (Swietenia macrophylla King) is the woody species with the highest economic value in Latin America. Currently, it is subject to intensive exploitation, diminishing its natural populations. Due to this decline, the species is a preferred species for reforestation and establishment of commercial tropical plantations. Mycorrhizal symbiosis is a biotic factor scarcely studied in the ecology of this species. Therefore, the objective of this research was to identify the diversity of arbuscular mycorrhizal fungi (AMF) species associated with the rhizosphere of seedlings and mature trees of big-leaf mahogany growing in its natural habitat, a tropical rain forest in Los Tuxtlas, Veracruz, Mexico. Soil samples from a 20-cm depth were taken from the rhizosphere of big-leaf mahogany seedlings and mature trees. Additionally, spores from the rhizosphere soil were propagated on Sorghum vulgare, isolated and identified. The percentage of AMF colonization was also evaluated.

RESUMENEste trabajo consistió en propagar e identifi car hongos micorrícicos arbusculares (HMA) recolectados de plantas medicinales (PM) de áreas naturales de bosques mixtos, y seleccionar consorcios micorrícicos con base en la promoción del crecimiento de vinca Catharanthus roseus (L) G. Don, planta medicinal cuyos alcaloides tienen propiedades antineoplásicas. En la primera fase experimental se recolectaron raíces y suelo rizosférico de 13 PM establecidas en campo para evaluar el porcentaje de colonización total (PCT) y cuantifi car el número de esporas; además, se tomó una parte del suelo para establecer plantas trampa en invernadero durante 10 meses, y posteriormente evaluar el PCT e identifi car los principales géneros de HMA. Todas las PM en su condición natural presentaron colonización micorrícica, obser vándose cuatro géneros de HMA (Glomus, Acaulospora, Gigaspora y Scutellospora), de los cuales Acaulospora y Glomus fueron los predominantes. En la segunda fase experimental se seleccionaron ocho consorcios con base en el PCT (> 40 %) obtenido en las plantas trampa, que correspondieron a las muestras recolectadas de Adiantum capillus-veneris L., Castilleja tenuifl ora Benth., Erigeron karvinskianus DC., Pimpinella anisum L., Plantago major L., Ricinus communis L., Rubus fruticosus L. y Rumex mexicanus Meisn. Estos consorcios fueron inoculados en plántulas de C. roseus para evaluar su capacidad de estimular el crecimiento de esta especie en condiciones de invernadero. Después de 70 días, a pesar de presentar un solo género predominante (Glomus), el consorcio aislado de R. mexicanus promovió de manera más consistente el crecimiento de C. roseus (número de hojas, área foliar y peso seco foliar) en comparación con el resto de los consorcios micorrícicos.Palabras clave: colonización micorrícica, cultivos trampa, planta medicinal, selección de hongos micorrícicos, simbiosis micorrícica. ABSTRACTThis study consisted on propagating and identifying arbuscular mycorrhizal fungi (AMF) collected from medicinal plants (MP) of natural areas of mixed forest (Estado de Mexico), and selecting mycorrhizal consortia based on the growth promotion of Catharanthus roseus (L) G. Don, medicinal plant whose alkaloids have antineoplasic properties. In the fi rst experimental stage, roots and rhizospheric soil were collected from the 13 MP in which the mycorrhizal colonization percentage (MCP) and the number of spores were assessed; in addition, soil samples were used for establishing culture traps under greenhouse conditions for 10 months and thus, the main AMF genera were identifi ed. All MP showed AMF colonization, and four fungal genera were identifi ed (Glomus, Acaulospora, Gigaspora, and Scutellospora) from which Acaulospora and Glomus were predominant. The second experimental stage allowed the selection of eight consortia based on the MCP of trap cultures (> 40 %), that corresponded to samples collected from Adiantum capillus-veneris L., Castilleja tenuifl ora Benth., Erigeron karvinskianus DC., Pimpinella anisum L., Plantago...

Mobilization and transfer of nine macro-and micronutrients to Pinus greggii seedlings via arbuscular mycorrhizal fungi Movilización y transferencia de nueve macro y micronutrientes a plántulas de Pinuss greggii a través de hongos micorrízico arbusculares