Growth and production of ornamental sunflower grown in the field in response to application of humic acids / Crescimento e produção de girassol ornamental cultivado em campo em resposta à aplicação de ácidos húmicos

The humic acid fraction of organic matter has a stimulating effect on the growth and development of ornamental plants. This study investigated the response in growth and yield of field-grown ornamental sunflower (Helianthus annuus L.) to the seed treatment with humic acids. The experiment was arranged in a randomized block design with three replications. Sunflower seeds were soaked in solutions of 0, 10, 20, 30, and 40mmol L-1 C in the form of humic acids and then sown in the flower beds. At harvest, the flower stems were collected to determine the variables: stem height, stem diameter, fresh stem weight, number of leaves per stem, leaf fresh weight per stem, leaf dry matter per stem, number of flower stalks, and diameter of the floral receptacle. Data were subjected to regression analysis. The results showed increases in all variables in response to the application of humic acids, except in number of leaves per stem, which remained unchanged. The greatest increases usually resulted from concentrations from 15 to 20mmol L-1 C in the form of humic acid. It was concluded that the seed treatment with humic acid at the indicated concentrations increases the number and commercial quality of flower stalks of field-grown ornamental sunflower.

Os ácidos húmicos, fração da matéria orgânica, apresentam efeitos estimulantes no crescimento e desenvolvimento de plantas ornamentais. O presente trabalho objetivou estudar o crescimento e produção de girassol ornamental (Helianthus annuus L.) em resposta à aplicação de ácidos húmicos em cultivo em campo. O delineamento estatístico foi o de blocos casualizados com três repetições. As sementes foram imersas nas soluções de 0, 10, 20, 30 e 40mmol L-1 de C na forma de ácidos húmicos e, posteriormente, semeadas em canteiros a campo. No momento da colheita, as hastes florais foram coletadas para medição das variáveis: altura da haste, diâmetro da haste, matéria fresca da haste, número de folhas por haste, matéria fresca foliar por haste, matéria seca foliar por haste, número de hastes florais e diâmetro do receptáculo floral. Os dados foram submetidos à análise de regressão. Os resultados mostraram incrementos em todas as variáveis analisadas, em resposta à aplicação de ácidos húmicos, com exceção do número de folhas por haste, que não sofreu alteração. Os maiores incrementos foram, em geral, proporcionados em concentrações entre 15 a 20mmol L-1 de C na forma de ácidos húmicos. Conclui-se que o uso dos ácidos húmicos nas concentrações indicadas aumenta o número e a qualidade comercial das hastes florais de girassol ornamental cultivado em campo.

Structural interaction between GFP-labeled diazotrophic endophytic bacterium Herbaspirillum seropedicae RAM10 and pineapple plantlets 'Vitória'

The events involved in the structural interaction between the diazotrophic endophytic bacterium Herbaspirillum seropedicae, strain RAM10, labeled with green fluorescent protein, and pineapple plantlets 'Vitória' were evaluated by means of bright-field and fluorescence microscopy, combined with scanning electron microscopy for 28 days after inoculation. After 6 hours of inoculation, H. seropedicae was already adhered to the roots, colonizing mainly root hair surface and bases, followed by epidermal cell wall junctions. Bacteria adherence in the initial periods occurred mainly in the form of solitary cells and small aggregates with pleomorphic cells. Bacteria infection of root tissue occurred through the cavities caused by the disruption of epidermal cells during the emergence of lateral roots and the endophytic establishment by the colonization of intercellular spaces of the cortical parenchyma. Moreover, within 1 day after inoculation the bacteria were colonizing the shoots. In this region, the preferred sites of epiphytic colonization were epidermal cell wall junctions, peltate scutiform trichomes and non-glandular trichomes. Subsequently, the bacteria occupied the outer periclinal walls of epidermal cells and stomata. The penetration into the shoot occurred passively through stoma aperture followed by the endophytic establishment on the substomatal chambers and spread to the intercellular spaces of spongy chlorenchyma. After 21 days of inoculation, bacterial biofilm were seen at the root hair base and on epidermal cell wall surface of root and leaf, also confirming the epiphytic nature of H. seropedicae.

Phylloepiphytic interaction between bacteria and different plant species in a tropical agricultural system.

Plant surfaces are a favourable niche for bacterial establishment, and hypothetically, plant species differ in their capacity to harbour epiphytic bacterial communities. This study was conducted to evaluate and describe the structural relationship of a bacterial community at the phyllosphere level with different plant species in a tropical ecosystem. Leaf blades of 47 plant species distributed in 27 botanical families were collected on a typical small Brazilian farm and prepared for observation under light and scanning electron microscopy. Naturally occurring bacteria were the most abundant settlers of the phylloplane, followed by fungal spore or hyphae. All plant species studied were colonized by phylloepiphytic bacteria, which were observed as solitary cells, microcolonies, and biofilms. However, independent of the family, the plant species differed in the pattern of phyllosphere colonization, as reflected in bacteria frequency and presence or absence of anatomical features that would favour the association. The phylloepiphytic bacteria were preferentially established on the following sites: epidermal cell wall junctions, glandular and nonglandular trichomes, veins, stomata, and epidermal cell wall surface. Profuse bacteria and fungi colonization was observed, at a level that was at least comparable with temperate regions. Interestingly, fungi seemed to alter the bacteria colonization pattern, most probably by microenvironmental modifications. The trichome type and density as well as the presence of epicuticular wax on the leaf blade surface seemed to be the most determinant anatomical features for the pattern of phyllosphere colonization. The presence of trichomes has a favourable, and epicuticular wax an unfavourable influence on the plant-bacteria interaction.