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To develop proposals in bacterial formulations applicable to the agricultural sector, a study of physicochemical and biological parameters of the polymeric materials is essential. Here, we evaluated the effects of eight polymers on the cellular viability of Rhizobium sp. G58 during a 2-month period. From these results, we selected the three polymers that yielded the best results in respect to the survival of the bacteria. An assay of the effect of the polymers on the symbiotic activity of Rhizobium-Cowpea and the agronomic parameters was conducted under greenhouse conditions, based on the principal component analysis. A positive effect was found in Rhizobium sp. G58 using the Tukey's Test (p<0.05) with sodium alginate (0.5-1%) and hydroxypropyl methylcellulose-HPMC (0.125-0.5%), while a significant decrease was established in cellular viability using polyethylene glycol-PEG, carbomer-Carbopol 940, and polyvinyl alcohol-PVA. The multivariate analysis indicated that the application of the polymers (sodium alginate and hydroxypropyl methylcellulose) in 0.5% concentration did not have negative effects on the symbiotic fixation of nitrogen or the process of nodulation. In conclusion, our results suggest the effectiveness of these polymers and the possibility of using them as carriers of bacterial formulation without affecting physiological processes.

Artícu lo cI ENtíF IcoM i c r o b i o l o g í a d e l s u e l o Effect of plant growth-promoting rhizobacteria (PGPR) associated to Pennisetum clandestinum in the altiplano cundiboyacense A B S T R A C TPennisetum clandestinum (kikuyo) is a common pasture in the altiplano cundiboyacense silvopastoral systems, which possesses high nutritional value. Therefore, studies to improve the production process in both economic and environmental terms are very important. The role of inoculation with plant growthpromoting bacteria was evaluated on the growth of kikuyu grass. The 4K and 5B strains were identified, through amplification and analysis of their 16S rDNA, as members of the Stenotrophomonas and Pseudomonas genera, respectively. They were characterized in vitro for their efficiency of biological nitrogen fixation, production of indole compounds, and phosphate solubilization. Four treatments were evaluated under greenhouse conditions. Furthermore, the biomass was evaluated at different stages of the plant (70, 100 and 130 days). The 4K strain demonstrated a root dry weight that increased by 50% at 70 and 100 days and the 5B strain showed a statistically significant behavior for plant and root dry weight with an increase of 50% at 130 days. The most important effect was presented after 100 d where treatments, TQ, TB1 and TB2, exceeded more 80% to absolute control in the fresh weight of the air. These results showed that inoculation with PGPR represents a biotechnological alternative to promote growth of P. clandestinum, as we observed relevant effects on biomass production 100 days after planting.

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Aim of study: The objective of this work is to examine wood properties of a mixed plantation of Samanea saman and Enterolobium cyclocarpum, combined with native species of Costa Rica.Area of study: Mixed plantation in dry tropical zone of Costa Rica.Material and Methods: It was measured by total diameter, heartwood, bark thickness, several physical wood properties (green density, specific gravity, volumetric, tangential and radial shrinkage and moisture content) and wood color.Main results: The largest of this diameter are reached when S. saman is planted with E. cyclocarpum, E. cyclocarpum and Swietenia macrophylla and Simarouba glauca. Meanwhile the largest total diameter and heartwood in E. cyclocarpum was found when this species is planted with Dalbergia retusa. Heartwood percentage, bark percentage, and some physical properties are not affected when S. saman or E. cyclocarpum are planted with other species. However, parameters of wood color were affected mixture plantation of S. saman or E. cyclocarpum with other species. The lowest difference between wood from mixed plantations and wood from trees growing in native forests is produced when S. saman is mixed with E. cyclocarpum, but this last species is mixed with Hymenaea courbaril and produced wood with the lowest difference in wood color compared to trees growing in the natural forest.Research highlights: S. saman and E. cyclocarpum tress planted in a mixed plantation produce variation in breast diameter, physical properties, heartwood percentage and wood color.Keywords: silvicultural condition; wood properties; tropical species; plantation species.

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Se realizó una etapa exploratoria aplicando el diseño Plackett-Burman para cuatro fuentes de carbono, dos fuentes de nitrógeno, K2HPO4 y MgSO4 y una solución de micronutrientes con el fin de seleccionar los factores nutricionales más influyentes sobre el crecimiento del microorganismo. Posteriormente, se llevó a cabo un proceso de optimización aplicando el diseño Box-Behnken de los tres factores más influyentes; los resultados indicaron que la producción de biomasa (UFC/mL) fue afectada significativamente por condiciones tanto nutricionales como físicas del medio de cultivo; el máximo rendimiento obtenido fue de 1 X 109 UFC/mL, el cual se logró bajo las siguientes condiciones: 3 g/L sacarosa, 6,75 mL/L melaza, 0,77 mL/L glicerol, 14,42 mL/L hidrolizado de soya, 0,848 g/L hidrolizado de levadura, 0,25 g/L K2HPO4, 3/5 aireación y agitación a 120 rpm con un tiempo de fermentación de 26 horas.Palabras clave: Azospirillum brasilense, diseño Plackett-Burman, diseño Box-Behnken, superficie de respuesta.