Marco Antonio Martins

The Role of the external mycelial network of arbuscular mycorrhizal fungi: III. a study of nitrogen transfer between plants interconnected by a common mycelium

An experiment under greenhouse conditions was carried out to evaluate the relative contribuition of arbuscular mycorrhizal fungi (AMF) in the process of nitrogen transfer from cowpea to maize plants, using the isotope 15N. Special pots divided in three sections (A, B and C), were constructed and a nylon mesh screen of two diameters: 40µm (which allowed the AMF hyphae to pass but not the plant roots) or 1µm (which acted as a barrier to AM hyphae and plant roots) was inserted between the sections B and C. Section A had 25.5 mg of N/kg using (15NH4)2SO4 as N source. Two cowpea seedlings inoculated with Rhizobium sp. were transplanted with their root systems divided between the sections A and B. Ten days later, 2 seeds of maize were sown into the section C which was inoculated with Glomus etunicatum. Thirty-five days after transplanting, the maize plants were harvested. AMF inoculation increased dry weight and 15N and P content of maize plant shoots. Direct transfer of 15N via AMF hyphae was 21.2%; indirect transfer of 15N mediated by AMF mycelium network, was 9.6%, and indirect transfer not mediated by AM mycelium network , was 69.2%.

Crescimento e composição mineral da menta em resposta à inoculação com fungos micorrízicos arbusculares e adubação fosfatada

The effects of arbuscular mycorrhizal fungi (AMF) were evaluated on the growth and mineral composition of Mentha arvensis L., grown under different phosphorus levels. The experiment was carried out in a greenhouse, in a factorial scheme 5x4, with five microbiological treatments (control without AMF, Glomus clarum, Glomus etunicatum, Gigaspora margarita and Acaulospora scrobiculata) and four P levels (0; 50; 100 and 200 mg kg-1). A randomized block design was used, with four replications. The plants were harvested at flowering, 65 days after planting. When no phosphorus was added, Gigaspora margarita and Glomus clarum led to a higher percentage of mycorrhizal colonization in roots and increased 334 and 330% the dry matter production of shoots, 143 and 123% the N content, 224 and 124% the P content, 139 and 142% the K content, respectively. The AMF inoculation did not influence Ca, Mg, S, Fe and Zn contents. Dry matter production was higher under P doses from 122 to 165 mg kg-1 of soil. In such doses, Mn content was lower when the plants were inoculated with Glomus clarum, Gigaspora margarita and Glomus etunicatum. The mycorrhizal dependence of the mint varied with microbiological treatments and P levels, being higher with Glomus clarum and Gigaspora margarita, under no phosphorus addition.

Arbuscular mycorrhizal fungi and the occurrence of flavonoids in roots of passion fruit seedlings

Composition and the role of root flavonoids in the regulation of mycorrhizal symbiosis are still poorly understood. Several flavonoids stimulate spore germination, mycelia growth and root colonization by arbuscular mycorrhizal fungi (AMF), and both root colonization and flavonoid composition are affected by plant nutritional status. Effects of AMF on the occurrence and content of aromatic secondary metabolites in the roots of passion fruit seedlings grown under two levels of phosphorus (P) fertilization (10 and 50 mg kg-1 of phosphorus) was studied. Seedlings were inoculated with Glomus clarum and a population of native fungi from a passion fruit plantation. Methanolic extracts of passion fruit seedlings roots were analyzed by high performance liquid chromatography (HPLC). It was recorded the occurrence of several compounds, possibly flavonoids, with seven major peaks. The root contents of the compound with a retention time of 4.5 minutes, varied in response to the root colonization by different mycorrhizal fungi, and the contents of two compounds with retention times of 3.4 and 18.9 minutes varied due to the poor plant growth and nutritional status. Passion fruit seedlings have several aromatic compounds, and their contents were correlated with root colonization by different mycorrhizal fungi, the reduced seedling growth due to nutritional stress, and/or the plant defense responses to the fungi.

Crescimento de mudas micropropagadas de bananeira micorrizadas em diferentes recipientes

Realizou-se um experimento em casa de vegetacao, com o objetivo de avaliar a utilizacao de diferentes recipientes e a eficiencia da inoculacao com fungo micorrizico arbuscular (FMA), Glomus clarum, no crescimento de mudas micropropagadas de bananeira. O delineamento experimental foi o de blocos casualizados, no esquema fatorial 2x2, sendo 2 tratamentos microbiologicos: Glomus clarum e controle; e 2 recipientes: blocos prensados e tubetes, com 6 repeticoes. O substrato utilizado para a confeccao dos blocos e para o enchimento dos tubetes foi constituido por uma mistura de materiais orgânicos (bagaco de cana + torta de filtro de usina acucareira) e vermiculita. Mudas de bananeira produzidas em blocos prensados e inoculadas com o FMA apresentaram melhores resultados quando comparadas com as produzidas nos tubetes, com incrementos na altura, na producao de materia seca da parte aerea e no acumulo de N, P e K de 90%, 829%, 2774%, 249% e 403%, respectivamente.