ABSTRACT The effects of different nitrogen doses on dry weight yield, stevioside and rebaudioside A contents, and yields were evaluated in stevia (Stevia rebaudiana Bertoni). This study was carried out at the Instituto Federal Catarinense, Rio do Sul (SC), Brazil, under decreasing photoperiods. A randomized complete block design with four blocks and five treatments (0, 65, 135, 200 and 270 kg ha-1 N) was used. Variables related to dry weight yield (total dry weight, leaf dry weight, stem dry weight, number of secondary branches and tertiary branches, and main stem length), growth rates (total leaf area, leaf area index, specific leaf area, leaf area ratio, leaf weight ratio), and stevioside and rebaudioside A contents and yields were evaluated. The doses of nitrogen fertilization did not affect the variables related to dry weight yield, stevioside and rebaudioside A contents and yields, or rebaudioside A:stevioside ratio in stevia genotype 8 (G8), grown under decreasing photoperiods.

RESUMEN El efecto de diferentes tasas de nitrógeno en la producción de biomasa, el contenido y rendimiento de esteviósido y rebaudiósido A en el cultivo de estevia se evaluaron en un experimento de campo en el Instituto Federal Catarinense, Rio do Sul (SC), Brasil, en condiciones de fotoperíodo decreciente. Se utilizó un diseño de bloques completos al azar con cuatro bloques y cinco tratamientos (0, 65, 135, 200 y 270 kg ha-1 N). Se evaluaron las variables relacionadas con la producción de biomasa (DM total, tallo MS, hojas MS, número de ramas secundarias, número de ramas terciarias y longitud de rama más grande), variables relacionadas con los índices de crecimiento (AFT, IAF, AFE, RAF y RPF) y también variables relacionadas con el contenido y el rendimiento de esteviósido y rebaudiósido A. Las diferentes dosis de fertilización nitrogenada no afectaron las variables relacionadas con la acumulación de materia seca en el genotipo G8 cultivado en condiciones de fotoperíodo decreciente en las condiciones de campo. Los niveles de fertilización nitrogenada no afectaron los niveles de esteviósido y rebaudiósido A, la productividad de esteviósido y rebaudiósido A y la proporción de rebaudiósido A / esteviósido en el G8 cultivado en condiciones de fotoperíodo de disminución de campo.

RESUMEN La evaluación de cuatro genotipos de estevia para la producción de biomasa, el contenido y rendimiento de esteviósido y rebaudiósido A, se llevó a cabo en la región de Alto Vale do Itajaí, estado de Santa Catarina, SC (Brasil), en condiciones de disminución de fotoperíodo. El experimento se realizó en el campo de la Granja São Miguel, Lontras, SC, Brasil, bajo condiciones de disminución del fotoperíodo, con una variación de 13.72 h de luz, en el momento de la implantación del experimento, a 12.57 h de luz al final de las evaluaciones. Los tratamientos fueron cuatro genotipos (G4, G8, G9 y G12), procedentes de EMBRAPA-CENARGEN. Se utilizó un diseño de bloques completos al azar con cuatro tratamientos (genotipos de estevia) y cuatro repeticiones. Cada parcela constaba de 21 plantas y el área del piso por cinco plantas. G12 tuvo el mayor peso seco de la hoja (PSH), área foliar total, índice de área foliar, relación de área foliar y área foliar específica de todos los genotipos. G4 y G12 presentaron similitud en PSH, siendo superiores a los demás, con producción de 755,6 y 836,4 kg ha-1, respectivamente. El contenido de esteviósido fue mayor en G12 (200.07 mg g-1). G8 y G9 fueron iguales para el contenido de rebaudiósido A, presentando 64,77 y 49,05 mg g-1, respectivamente. La relación rebaudiósido A: esteviósido fue mayor en el genotipo G8 (0,44 g g-1). Ningún genotipo evaluado bajo las condiciones productivas del Alto Vale do Itajaí presentó la relación rebaudiósido A: esteviósido apropiada requerido para la industria.

ABSTRACT An evaluation of four stevia genotypes for biomass yield, stevioside and rebaudioside A content and yield under decreasing photoperiod conditions was carried out in the Alto Vale do Itajaí region, located in the State of Santa Catarina (SC), Brazil. This field experiment was conducted at Site São Miguel, a farm located in the city of Lontras (SC), Brazil, under conditions of decreasing photoperiods, with a variation of 13.72 h of light at experiment implantation to 12.57 h of light at the end of the evaluations. The treatments consisted of four genotypes (G4, G8, G9 and G12) provided by EMBRAPA-CENARGEN. A randomized complete block design with four treatments (stevia genotypes) and four replications was used. Each plot consisted of 21 plants, and the floor area had five plants. G12 had the highest leaf dry weight (LDW), total leaf area, leaf area index, leaf area ratio and specific leaf area of all the genotypes. G4 and G12 were equal for LDW and were higher than the other genotypes, with yields of 755.6 and 836.4 kg ha-1, respectively. The stevioside content was highest in G12 (200.07 mg g-1). G8 and G9 were similar for rebaudioside A content (64.77 and 49.05 mg g-1, respectively). The rebaudioside A: stevioside ratio was highest in G8 (0.44 g g-1). No genotype had a rebaudioside A: stevioside ratio suitable for industry requirements.

Abstract Stevia (stevia rebaudiana Bertoni) is a species characterized by producing non-caloric substances with high sweetening potential. Among these substances, rebaudioside A and stevioside are produced in greater quantity. Plant density and harvesting time are factors that affects biomass and sweetening compounds yield in this species. The objective of this research was to evaluate the effect of plant densities and harvesting times on the productive and physiological characteristics of stevia in southern Brazil. The experimental design was in randomized blocks, in a split-plot scheme, with 9 treatments comparing the effect of three planting densities (166 667, 83 333 and 33 333 plants ha-1) in the plots and three harvesting periods (before, in the beginning and in full flowering) in the subplots. Harvesting at the beginning of flowering promoted higher dry leaf biomass yield and, when associated with the lowest planting density, promoted higher levels of rebaudioside A and stevioside. The lowest planting density resulted in greater leaves biomass accumulation, whereas the highest density promoted higher yields per area. Interaction between density of 166 667 plants ha-1 and the harvest at the onset of flowering promoted higher yields of rebaudioside A (43.22 kg ha-1) as well as higher rebaudioside A/stevioside ratio (0.60).

Abstract: INTRODUCTION: The significant increase in dengue, Zika, and chikungunya and the resistance of the Aedes aegypti mosquito to major insecticides emphasize the importance of studying alternatives to control this vector. The aim of this study was to develop a controlled-release device containing Piper nigrum extract and to study its larvicidal activity against Aedes aegypti. METHODS: Piper nigrum extract was produced by maceration, standardized in piperine, and incorporated into cotton threads, which were inserted into hydrogel cylinders manufactured by the extrusion of carrageenan and carob. The piperine content of the extract and thread reservoirs was quantified by chromatography. The release profile from the device was assessed in aqueous medium and the larvicidal and residual activities of the standardized extract as well as of the controlled-release device were examined in Aedes aegypti larvae. RESULTS The standardized extract contained 580mg/g of piperine and an LC50 value of 5.35ppm (24h) and the 3 cm thread reservoirs contained 13.83 ± 1.81mg of piperine. The device showed zero-order release of piperine for 16 days. The P. nigrum extract (25ppm) showed maximum residual larvicidal activity for 10 days, decreasing progressively thereafter. The device had a residual larvicidal activity for up to 37 days. CONCLUSIONS: The device provided controlled release of Piper nigrum extract with residual activity for 37 days. The device is easy to manufacture and may represent an effective alternative for the control of Aedes aegypti larvae in small water containers.