O presente trabalho foi realizado com a finalidade de estudar alguns isolados de Pisolithus tinctorius quanto aos aspectos básicos de crescimento, características citológicas, padrão de esterases e obtenção de protoplastos e quanto ao potencial de infecção desses isolados em espécies de eucalyptus. A caracterização do crescimento em diferentes meios de cultura mostrou que os isolados AC 12, PI 314 e PI 203 apresentaram um bom crescimento em todos os meios testados e não apresentaram diferenças quanto a produção de biomassa nos diferentes meios. Na analise citológica, verificou-se que cada célula micelial possui dois núcleos e a presença de pontes de conexão entre as células. A mitose e similar a que ocorre em outros fungos com agregação dos cromossomos formando duas barras paralelas. Os isolados obtidos de pinus apresentaram um padrão eletroforético de esterases com quatro bandas. Quanto à obtenção de protoplastos, fez-se a avaliação de algumas condições para o isolamento dos mesmos. Quanto aos aspectos mais práticos, foram obtidos e selecionados novos isolados. O problema da falha de micorrização foi eliminado inoculando-se plântulas ao invés de sementes

The present research was carried out in order basic of growth, characteristics, aspects patterns of esterases and cytological protoplast isolation of some isolates of Pisolithus tinctorius as well as their potential of mycorrhizal infection in Eucapyptus. Growth characteristics in different media has shown that the isolates AC 12, PI 314 and PI 203 had good growth in alI of them, while the other ones showed changes in mycelium growth and didn't show a difference in the biomass production. Cytological analysis of these isolates indicated that the hyphae had different widths, each mycelial cell had two nuclei with a diameter of 2.439 μm and the presence of clamp connexion between the cells. The study of the nucIei during the division of somatic cells showed that the mitosis is similar to that which occurs in other fungi, with the chromossomes forming two paraIleI bars.The cromossome number could not be determinated. Pisolithus tinctorius isolated from Pinus showed an eletrophoretic pattern of esterase with four bands. For the Eucalyptus isolates, there were no satisfactory results. An evaluation of different conditions was made for the isolation of protoplasts. Optimal yield were obtained with four day old mycelia, Novozym 234 and the osmotic stabilizer, mannitol. For practical aspects, some strains were evaluated for their potential in mycorrhizal infection on Eucalyptus species in different concentrations of iron. The results were not satisfactory because of the failure to obtain infection of the plants. New strains were isolated and among them AT 501 and AT 502 were selected for Eucalyptus urophylla and E. paniculata and AT 502 and AT 508 for E. torelliana. The other strains did not infect more than 50% of the plants. In order to try to overcome problem the inoculation of a few plants instead inoculation of seeds, was made. With this alteration, problem of non infection was solved, probably because this of the fungi grown on particles of vermiculite were not able to survive during the period of root formation, when inoculated on seeds