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Resumo -O objetivo deste trabalho foi avaliar o efeito de aplicações de Mycoform na colonização micorrízica e esporulação de 13 isolados de fungos micorrízicos arbusculares em Brachiaria decumbens. O experimento foi conduzido em casa de vegetação, em solo esterilizado, com delineamento experimental inteiramente casualizado, em arranjo fatorial 3x13, com cinco repetições. O produto foi aplicado no plantio e foi ou não aplicado uma segunda vez 60 dias depois, na quantidade de 2 mg kg -1 de solo. Aos 150 dias de crescimento das plantas, foram coletadas amostras de raízes e de solo rizosférico, para a avaliação de colonização radicular e densidade de esporos. Houve estímulo do Mycoform nos parâmetros avaliados, efeito que variou com os isolados estudados. Foi observado efeito significativo da aplicação do Mycoform na colonização das raízes pelos isolados Glomus clarum DCS 09 e DCS 10, Paraglomus occultum DCS 06 e Acaulospora delicata DCS 02 e na esporulação dos isolados G. clarum DCS 09 e DCS 10, P. occultum DCS 06 e DCS 31, Glomus etunicatum DCS 12, A. delicata DCS 30 e Kuklospora colombiana DCS 03. O incremento na esporulação atingiu 89% e, na colonização, 60%, o que confirma os benefícios da formononetina na colonização e na esporulação dos fungos micorrízicos arbusculares.Termos para indexação: Brachiaria decumbens, estimulante de micorriza, multiplicação de FMAs, Mycoform, simbiose radicular. Formononetin application on colonization and sporulation of arbuscular mycorrhizal fungi in BrachiariaAbstract -The aim of this work was to evaluate the effects of Mycoform on both sporulation and colonization of 13 arbuscular mycorrhiza fungi (AMF) isolates in Brachiaria decumbens. The experiment was carried out in greenhouse conditions with sterile soil, in a completely randomized design with 3x13 factorial treatments and five repetitions. The product was applied once at planting and was or was not applied a second time 60 days afterwards, at an amount of 2 mg kg -1 of soil. Plants were allowed to grow for 150 days, when root and rhizospheric soil samples were collected to evaluate the percentage of colonized root segments and the spore density. Mycoform effects were different among the fungal isolates. It had significant effect on colonization for the isolates Glomus clarum DCS 09 and DCS 10, Paraglomus occultum DCS 06 and Acaulospora delicata DCS 02, and on spore density for the isolates G. clarum DCS 09 and DCS 10, P. occultum DCS 06 and DCS 31, Glomus etunicatum DCS 12, A. delicata DCS 30 and Kuklospora colombiana DCS 03. Maximum increases due to Mycoform were 60% for colonization and 89% for spore density. These results confirm formononetin effects on AMF colonization and on AMF sporulation.Index terms: Brachiaria decumbens, mycorrhizal stimulate, AMF multiplication, Mycoform, root symbiosis. IntroduçãoA produção agrícola sustentável está associada ao desenvolvimento de tecnologias que minimizem os impactos ambientais e que poupem insumos não renováveis, como os fertilizantes a base de fósforo. Nesse sentido, há gra...

Arbuscular mycorrhizal fungi (AMF), which live in symbiosis with 80 % of plants, are not able to grow when separated from their hosts. Spore germination is not host-regulated and germling growth is shortly arrested in the absence of host roots. Germling survival chances may be increased by hyphal fusions (anastomoses), which allow access to nutrients flowing in the extraradical mycelium (ERM). Perfect anastomoses, occurring with high frequency among germlings and the ERM of the same isolate, show protoplasm continuity and disappearance of hyphal walls. A low frequency of perfect fusions has been detected among co-specific genetically different isolates, although fungal nuclei have been consistently detected in all perfect fusions, suggesting active nuclear migration. When plants of different taxa establish symbioses with the same AMF species, anastomoses between ERM spreading from single root systems establish a common mycelium, which is an essential element to plant nutrition and communication. The interaction among mycelia produced by different isolates may also lead to pre-fusion incompatibility which hinders anastomosis formation, or to incompatibility after fusion, which separates the hyphal compartments. Results reported here, obtained by analyses of hyphal compatibility/ incompatibility in AMF, suggest that anastomosis formation and establishment of protoplasm flow, fundamental to the maintenance of mycelial physiological and genetic continuity, may affect the fitness of these ecologically important biotrophic fungi.

For a single plant species under the same environmental conditions, the interaction with arbuscular mycorrhizal fungi (AMF) and their contribution to plant growth varies among AMF isolates, with both inter and intraspecific variability. The present study evaluated the functional variability of 41 isolates of 20 species and eight genera of AMF for root colonization, growth promotion, and P uptake of corn and observed the relationship of this functional variability with the isolates genetic variability revealed by PCR-RFLP analysis. All the isolates abundantly colonized the corn roots, but only 23 promoted higher shoot dry mass and P leaf content. The cluster analysis based on functional variability data separated the isolates Acaulospora morrowiae (Am2), Acaulospora sp. (Aca), A. colombiana (Ac3, Ac4, and Ac5), Gigaspora albida (Gia1), Gi. margarita (Gim4 and Gim5), Gi. rosea (Gir), Rhizophagus clarus (Rc2, Rc3, Rc4, Rc5, and Rc6), Claroideoglomus etunicatum (Ce4), R. manihotis (Rm), Scutellospora calospora (Sc), S. heterogama (Sh2, Sh3, Sh4, and Sh5) and S. pellucida (Sp3) from the others at the distance of 80% functional similarity. These were considered efficient in promoting functional symbiosis in corn while the other isolates were considered inefficient. The cluster analysis obtained by the PCR-RFLP technique was partly coherent with the species classification based on spore morphology. The isolates of R. clarus fell into one cluster and the isolates of the Gigaspora and Scutellospora genera (Gigasporaceae family) were clustered in a second cluster, without the ability to separate the species of these genera.

Arbuscular mycorrhizal fungi (AMF) play a key role in plant nutrition and in the maintenance of soil fertility in agroecosystems, but their survival can be affected by different agricultural practices, including the use of pesticides. In this work, we assessed the impact of chemicals with herbicidal and fungicidal activity on mycelial growth and structure of the worldwide distributed AMF Funneliformis mosseae. Results showed that mycelial growth and interconnectedness of three different F. mosseae lineages were affected by the chemicals tested at concentrations lower than those indicated for agricultural use. Indeed, benomyl reduced mycelial growth in one lineage and fenhexamid negatively affected germlings growth in the three lineages, while both fungicides significantly affected mycelial viability and induced abnormal hyphal branching. The three F. mosseae lineages showed sensitivity to herbicides, with significant growth and viability decreases in the presence of the active ingredient glufosinate ammonium and a low viability at increasing concentrations of dicamba. Anastomosis rates were reduced by the two fungicides and by very low levels of the herbicide glufosinate, whose impact on AMF networks should be further investigated, given its wide use in agriculture. Our results suggest that the use of some pesticides in agroecosystems may lead to growth reduction and disruption of AMF mycelial structural traits, even in AMF species able to tolerate soil disturbance, posing serious threats to AMF symbiotic performance and to the maintenance of soil mycorrhizal potential.

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Apesar de o zinco (Zn) ser micronutriente fundamental para o crescimento e metabolismo das plantas, quando presente em níveis tóxicos no ambiente pode afetar o desenvolvimento vegetal. Entre os vários efeitos benéficos do silício (Si), cita-se sua influência na diminuição ou eliminação dos efeitos adversos de metais pesados no meio. O objetivo deste trabalho foi avaliar o efeito do Si na amenização da toxidez de Zn sobre o crescimento e nutrição mineral de plantas de Eucalyptus urophylla. As plantas foram cultivadas em vasos contendo 3 L de solução nutritiva de Clark, em esquema fatorial 6 x 2, sendo seis concentrações de Zn (0, 2, 50, 150, 300 e 450 µmol L-1 como ZnSO4 7H2O) e duas de Si (0 e 1,78 mmol L-1 de Si como silicato de potássio). Após oito semanas, avaliaram-se alguns parâmetros morfológicos das plantas, produção de matéria seca, teores e utilização de nutrientes. O aumento das concentrações de Zn na solução nutritiva proporcionou maior fitotoxicidade nas raízes em relação à parte aérea. A adição do Si amenizou o efeito negativo do excesso de Zn sobre o crescimento, no entanto pouco influenciou os teores dos nutrientes avaliados nos tecidos, embora tenha proporcionado utilização mais eficiente de P, Ca, Mg e S pelas plantas de Eucalyptus urophylla.

Hyphal anastomoses which play a key role in the formation of interconnected mycorrhizal networks and in genetic exchange among compatible individuals have been studied in a limited number of species and isolates of arbuscular mycorrhizal fungi (AMF), mainly in symbiotic mycelium. In this work, the occurrence and frequency of anastomosis between hyphae of the same and different germlings were assessed in tropical isolates belonging to Acaulospora, Claroideoglomus, Gigaspora, Glomus, Rhizophagus and Scutellospora. Germlings belonging to Acaulospora, Claroideoglomus, Glomus and Rhizophagus formed perfect hyphal fusions, with frequencies ranging from 9.29 ± 3.01 to 79.84 ± 4.39 % within the same germling and from 14.02 ± 7.36 to 91.41 ± 3.92 % between different germlings. Rare fusions, occurring within the same hypha, were detected in Gigaspora species, and no anastomoses were observed in Scutellospora species. The consistent detection of nuclei in perfect fusions suggests that nuclear migration is active both within and between germlings. Present data on anastomosis formation, nuclear migration and germling viability in tropical isolates of AMF widen our knowledge on the extensive and consistent occurrence of successful hyphal fusions in this group of beneficial symbionts. The ability to anastomose and establish protoplasm flow, fundamental for the maintenance of physiological and genetic continuity, may produce important fitness consequences for the obligately biotrophic AMF.