Consistency of response to arbuscular mycorrhizal (AM) inoculation is required for efficient use of AM fungi in plant production. Here, we found that the response triggered in plants by an AM strain depends on the properties of the soil where it is introduced. Two data sets from 130 different experiments assessing the outcome of a total of 548 replicated single inoculation trials conducted either in soils with a history of (1) high input agriculture (HIA; 343 replicated trials) or (2) in more pristine soils from coffee plantations (CA; 205 replicated trials) were examined. Plant response to inoculation with different AM strains in CA soils planted with coffee was related to soil properties associated with soil types. The strains Glomus fasciculatum-like and Glomus etunicatum-like were particularly performant in soil relatively rich in nutrients and organic matter. Paraglomus occultum and Glomus mosseae-like performed best in relatively poor soils, and G. mosseae and Glomus manihotis did best in soils of medium fertility. Acaulospora scrobiculata, Diversispora spurca, G. mosseae-like, G. mosseae and P. occultum stimulated coffee growth best in Chromic, Eutric Alluvial Cambisol, G. fasciculatum-like and G. etunicatum-like in Calcaric Cambisol and G. manihotis, in Chromic, Eutric Cambisols. Acaulospora scrobiculata and Diversispora spurca strains performed best in Chromic Alisols and Rodic Ferralsols. There was no significant relationship between plant response to AM fungal strains and soil properties in the HIA soil data set, may be due to variation induced by the use of different host plant species and to modification of soil properties by a history of intensive production. Consideration of the performance of AM fungal strains in target soil environments may well be the key for efficient management of the AM symbiosis in plant production.

Agave angustifolia Haw. se distribuye en la vertiente occidental de la Sierra Madre en Sonora, México, donde se utiliza para la elaboración del destilado denominado 'Bacanora'. Se muestreó rizosfera y raicillas de esta especie durante las cuatro estaciones del año, para evaluar su relación con hongos micorrízicos arbusculares (HMA) en tres poblaciones silvestres. La cantidad de esporas de HMA varió de 9200 a 43 500 esporas dm-3, que pertenecen a 32 morfotipos de Acaulospora (10), Archaeospora (2), Diversispora (1), Glomus (17) y Pacispora (2). La colonización micorrízica fluctuó de 4.8 a 24.9 %, la densidad visual de 0.43 a 0.51 %, el micelio intrarradical de 3.8 a 8.9 mg dm-3, y el micelio extrarradical de 31.1 a 93.4 mg dm-3. El análisis de correspondencia mostró que sodio, potasio y magnesio son los factores abióticos más importantes, y que los factores bióticos relevantes fueron las relaciones micelio extrarradical:micelio intrarradical y micelio extrarradical:peso seco de raicillas. Sin embargo, el análisis de correspondencia canónica mostró que la relación A. angustifolia-HMA es más compleja y no puede explicarse solamente con estos factores.

-A new species of arbuscular mycorrhizal fungi, Glomus candidum is described. The species produces spores singly in the soil. Spores are white to very pale yellow, usually globose to subglobose, 87-157 μm diam. Spore wall consists of two adherent layers. The outer layer is hyaline, mucilaginous, and stains very pale pink in Melzer's reagent. This layer can be observed in young spores and often degrades at maturity. The inner layer is hyaline and laminated, but occasionally the innermost group of laminae are pigmented a pale yellow to give the impression of two separated layers.Resumen -Se describe una nueva especie de hongo formador de micorrizas arbusculares, Glomus candidum. La especie produce esporas libres en el suelo. Las esporas son blancas a amarillo muy pálido, usualmente globosas a subglobosas, 87-157 µm de diámetro. La pared de la espora consiste en dos capas adherentes. La capa externa a menudo se degrada con la madurez, es hialina, mucilaginosa, y se tiñe, sólo en las esporas jóvenes, de rosado muy pálido en reactivo de Melzer. La capa interna es hialina y laminada, pero a veces el grupo más interno de láminas aparece pigmentado de amarillo claro dando la impresión de dos capas separadas.

A newly discovered glomalean fungus, Scutellospora crenulata, is described and illustrated. This species possesses a complex spore ornamentation composed of dome-like sub-polygonal papillae partly separated by pits. The presence of a "beaded" spore wall component is reported for the first time in a member of Gigasporaceae.Key words: arbuscular mycorrhizal fungus, Gigasporaceae, tropical soil, sclerophyllous shrubland.