José Oswaldo Siqueira

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Two isoflavonoids isolated from clover roots grown under phosphate stress were characterized as formononetin (7-hydroxy,4'-methoxy isoflavone) and biochanin A (5,7-dihydroxy,4'-methoxy isoflavone). At 5 ppm, these compounds stimulated hyphal growth in vitro and root colonization of an undescribed vesicular-arbuscular mycorrhiza, a Glomus sp. (INVAM-112).(More)
The effect of soil acidity on spore germination, germ tube growth and root colonization of vesicular-arbuscular mycorrhizal (VAM) fungi was examined using a Florida Ultisol. Soil samples were treated with 0, 4, 8 and 12 meq Ca/MgCO3/100 g soil and each lime level received 0, 240, and 720 ppm P as superphosphate. Corn (Zea mays L.) was planted in the soil(More)
Arbuscular mycorrhiza (AM) associations are of great importance in forest ecology and land rehabilitation in the tropics, but information on AM susceptibility, host dependence, and host responsiveness to the fungi is scarce. The present study was carried out under greenhouse conditions in a low-fertility soil with 29 woody species. There were very large(More)
Arbuscular mycorrhizal fungi (AMF) were surveyed for species richness and abundance in sporulation in six distinct land uses in the western Amazon region of Brazil. Areas included mature pristine forest and sites converted to pasture, crops, agroforestry, young and old secondary forest. A total of 61 AMF morphotypes were recovered and 30% of them could not(More)
The effects of the application of 0.25 or 1.0 mM p-coumaric acid, p-hydroxybenzoic acid, or quercetin on growth and colonization of clover (Trifolium repens L. cv. Ladino) and sorghum (Sorghum bicolor L.) roots by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith were studied. In general, soil application of these compounds at(More)
Imazaquin, imazethapyr and pendimethalin showed high toxicity to sorghum plants grown in a greenhouse soil mix. However, mycorrhizal sorghum plants were less affected by herbicide toxicity than non-mycorrhizal ones, at low to moderate herbicide concentrations. VAM herbicide safening effects were more evident on imazaquin-treated plants, than for those(More)
This work aimed to evaluate density of associative diazotrophic bacteria populations in soil and grass root samples from heavy metal contaminated sites, and to characterize isolates from these populations, both, phenotypically (Zinc, Cadmium and NaCl tolerance in vitro, and protein profiles) and genotypically (16S rDNA sequencing), as compared to type(More)
In recent decades, the concentration of trace elements has increased in soil and water, mainly by industrialization and urbanization. Recovery of contaminated areas is generally complex. In that respect, microorganisms can be of vital importance by making significant contributions towards the establishment of plants and the stabilization of impacted areas.(More)
The aim of this study was to evaluate the effects of lime, fertilizers, mycorrhizal fungi, and selected rhizobia strains on the growth of four woody legume species, Albizia lebbeck (L.) Benth., Enterolobium contortisiliquum (Vell.) Morong., Leucaena leucocephala (Lam.) de Wit, and Sesbania virgata (Cav.) Pers. in a low-fertility soil. The experiment was(More)
The aim of this work was to evaluate the occurrence of arbuscular mycorrhizal fungi (AMF) species diversity in soil samples from the Amazon region under distinct land use systems (Forest, Old Secondary Forest, Young Secondary Forest, Agroforestry systems, Crops and Pasture) using two distinct trap cultures. Traps established using Sorghum sudanense and(More)