Fungi in coastal tableland soils of northeastern Brazil:Preliminary results

Soil compaction causes reduced agricultural production due to limited root development resulting in reduced water and nutrient access. This is particularly true of soils of the Brazilian tablelands (similar to200000 km(2)) that are characterized by a naturally occurring compact subsoil horizon. Most of these soils have a coeso layer with a density that limits agricultural production. Deep plowing has been the main treatment to alleviate this problem. This study was carried out to identify some fungi associated with an Argissolo Amarelo coeso (Ultisol) in the coastal tableland, in northeastern Brazil (16degrees10' to 16degrees30'S and 39degrees05' to 49degrees40'W). The fungi were evaluated on soil samples from cultivated areas under natural forest, rubber tree (Hevea brasiliensis Willd.), pasture, and annual crops at 0 to 15 cm and 35 to 50 cm depths. The predominant groups (Penicillium spp and Dematiaceac), were analyzed by Random Amplified Polymorphic DNA (RAPD) molecular markers. Other identified groups included Monilia, Aspergillus and Eurotiaceae. The soil under annual cropping showed a trend to higher diversity of fungi. The presence of fungi in the coeso horizon illustrates the biological activity that occurs in a compact subsoil horizon and a probable interaction with the organic C. These preliminary results suggest that die presence, quantity, and activity of associated fungi and bacteria and root dynamics be studied to better understand the environmental and agricultural functioning of this subsurface horizon

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs.Donna Glassop, Sally E. Smith and Frank W. Smit