Effects of light and temperature on seed germination in Cecropia hololeuca Miq. (Cecropiaceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Seed germination in Miconia theaezans (Bonpl.) Cogniaux (Melastomataceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of light and temperature on seed germination in Tibouchina mutabilis (Vell.) Cogn. (Melastomataceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Temperatura, escarificação mecânica e substrato na germinação de sementes das palmeiras juçara e açaí

The propagation of 'juçara' and 'açaí' is done by seeds, but there is a great desuniformity in the germination process. In this way, the objective of this study was to verify the effect of temperature, mechanical scarification and substrate on seed germination of both species. Two experiments were conducted in a completely randomized design, with four replications each consisting of 25 seeds. The first was conducted with 14 treatments in factorial scheme 7 x 2, seven temperatures (20, 25, 30, 35, 20-30 and 25-35 °C and natural condition), with and without mechanical scarification. The second was constituted of eight treatments in factorial scheme 4 x 2, four substrates (sand, vermiculite, coconut fiber and soil + manure), with and without mechanical scarification. Seeds of 'juçara' palm present the highest mean percentage and germination speed index in alternating temperatures of 20-30 and 25-35 °C and natural condition and in substrates sand, vermiculite and coconut fiber. Temperatures of 30, 35, 20-30 and 25-35 °C and natural condition in all substrates tested were the most favorable condition for 'açai' seeds. The scarification of the seeds was favorable to the germination process of 'juçara' whereas the seeds of açaí does not need to be scarified.

Effect of temperature on seed germination of ornamental herbaceous perennials

Antirrhinum majus L. and Senecio douglasii DC. are herbaceous perennial ornamental plants used in landscaping. The multiplication of these plants is by seed; however, there are still doubts about the temperature that can provide higher rates and speed of germination. Thus the aim was to study the effect of temperature on seed germination of A. majus and S. douglasii. The study was conducted separately for each species. The experimental design was entirely randomized with six temperature conditions (temperature controlled constant of 20, 25, 30, 35°C and alternating temperatures of 20-30 and 25-35°C with a photoperiod of 12 hours) with four replications of 100 seeds each. Total germination percentage and germination rate were determined. The means were compared by Tukey test at 5%. For A majus the highest germination percentage was observed at 20°C that did not differ statistically from other temperatures. The highest germination rate was obtained at the temperature of 20 and 25°C. For S. douglasii seeds it was observed that the highest germination percentage and germination rate occurred at 20°C. The lower temperature showed the better percentage and germination rate for these species.

Duração do teste de germinação do capim-tanzânia

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeito de temperaturas alternadas sobre desenvolvimento de Aedes (Stegomyia) aegyoti (L.) (Diptera: Culicidae)

Aedes (Stegomyia) aegypti is a species of mosquitoes known to be the vector of diseases such as dengue and yellow fever, and a better understanding of aspects of their biology can help in the establishment of control strategies for the same. Several previous studies showed that temperature significantly affects the development of immature stages of insects. In general, higher temperatures (up to a threshold) accelerate the development of insects, and lower temperature retards the same. This rule also applies to mosquitoes, including Ae. aegypti. But not still know the effects of daily variation of temperature on the developmental stages of mosquitoes. And this detail is very important, since in natural breeding or artificial, The mosquitoes usually face temperature variations over a single day, which should interfere with its development until the emergence of the adult forms. For this reason, the objective of this study is to analyze the effect of alternating temperatures on the development of Ae. aegypti. To conduct the study, adults were collected active in the neighborhood Bela Vista Campus of UNESP - Rio Claro, SP, using a sweep net or using ovitraps for immatures, and the active search for breeding. Individuals collected were kept under experimental conditions in the laboratory. The adult samples were identified to species level, were considered for the experiments, only samples of Ae. aegypti. The insects were housed in plastic cages, suitable for creating flies. These were fed with sugar solution and blood meal on alternate days. The eggs obtained were used in the experiment with four different temperature regimes. The data collected were analyzed by evaluating whether the different treatments influenced the development of immature to adult, performing the Kruskal-Wallis test and the statistical software BioEstat. Statistical analysis of the sex ratio... (Complete abstract click electronic access below)

Qualidade e alterações estruturais do café arábica submetido a alternância da temperatura na secagem

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Improvement to the physical quality and imbibition pattern in seeds of candeia (Eremanthus incanus (Less.) Less.)

The objective of this work was to develop a methodology for seed processing and X-ray analysis and to study imbibition pattern in seeds of candeia (Eremanthus incanus). Seeds were gathered in 2001 and 2002 in Morro do Pilar and Lavras respectively, processed and stored in a cold chamber (5ºC/60%RH) until the start of experiments. In order to identify unfilled seeds, a protocol was developed for X-ray use combining radiation energy (Kv) and exposure time (seconds). For elimination of unfilled seeds, an experiment was conducted using a South Dakota seed blower whereby different opening settings and ventilation times were combined. Original seed lots and categorized lots following radiograph viewing were tested by germination tests, with seeds being cleansed in sodium hypochlorite and scattered over blotting paper in 'gerboxes' and then taken to germinators with alternating temperatures of 20º-30ºC and 10 hours of light, for up to 15 days. Imbibition curves were determined under the conditions 30ºC, 20º-30ºC/10 hours of light and 30º-20ºC/10 hours of light. The X-ray protocol that best allowed viewing of internal seed structures was 30Kv for 45 seconds. Seed separation using the blower setting at a 3.0 opening for 30 seconds raised the number of embryonic seeds to values exceeding 99%, also raising the germination rates as a consequence. The imbibition pattern is three-phased and the germination process is completed in 72 hours. Under alternate temperatures, primary root growth is favored.

Germinación y crecimiento inicial de Habranthus gracilifolius y Rhodophiala bifida, amarilidáceas nativas con potencial ornamental

La azucena del campo (Az-del campo) (Habranthus gracilifolius) y la azucenita colorada (Az-colorada) (Rhodophiala bifida) son bulbosas nativas de Argentina de valor ornamental potencial, de las que se tiene escasa información sobre la germinación y el crecimiento. Para establecer la aptitud germinativa, el régimen de incubación más adecuado, y el crecimiento de las hojas y los bulbos, se realizó un ensayo de germinación y las plántulas se cultivaron en macetas durante un año. Se emplearon cuatro regímenes de incubación: temperatura constante de 20°C y alternadas de 20°/30°C y de 10°/20°C, todos con 8 horas de luz, y de 10°/20°C en oscuridad. Las semillas resultaron fotoblásticas neutras. A temperaturas de 20°C o de 10°/20°C, en ambas especies, la energía y el poder germinativo superaron el 75 y 92%, respectivamente, pero temperaturas de 20°/30°C demoraron la germinación. De otoño a fin de primavera las plantas presentaron hasta 4 hojas en Az-del campo y 2,5 hojas/ planta en Az-colorada, pero en verano no exhibieron hojas. Los bulbos presentaron crecimiento lineal, siendo mayores las tasas en Az-del campo (ancho = 0,022 y longitud = 0,049 mm.día-1) que en Az-colorada (ancho = 0,011 y longitud = 0,014 mm.día-1). La multiplicación por semillas es efectiva, pero en ambas especies se necesita más de un año para alcanzar el estadio reproductivo.

Seed germination characteristics of Phillyrea angustifolia L. and P. latifolia L. (Oleaceae), two Mediterranean shrub species having lignified endocarp

The aim of this study was to determine the germination characteristics of Phillyrea angustifolia L. and P. latifolia L. seeds in order to develop an optimized propagation protocol for Phillyrea species. Seeds of P. angustifolia and P. latifolia were collected from wild plants growing in Cáceres province (CW Spain) and Andalucía (S Spain), respectively. Percentage of water uptake for P. latifolia seeds was calculated. Seeds with and without endocarp were germinated at different constant and alternating temperatures. Seeds without endocarp were soaked in distilled water or gibberellic acid, and then set to germinate. Seeds with endocarp of both species were stratified at 5 ºC for 30 or 90 days and then the endocarp was completely removed from the seeds before they were sowed. Chemical scarification with sulfuric acid and mechanical scarification were tested on P. angustifolia seeds with endocarp. Phillyrea endocarp was permeable to water, since Phillyrea seeds with endocarp imbibed water, but water uptake was faster when the endocarp was removed. Moreover, the encodarp could interfere mechanically in the emergence of the radicle, since seed germination of Phillyrea species was promoted by the complete removal of the lignified endocarp surrounding each seed. Optimal germination temperature for both species was 15 ºC, and lower temperatures produced secondary dormancy. Soaking in distilled water or gibberellic acid did not significantly enhance seed germination. Cold stratification and chemical scarification treatments were detrimental for seed germination. Keywords cold stratification, Phillyrea species, treatments before sowing, seed germination, seed scarification, lignified endocarp.

Numerical estimation of hotspot temperatures in electrodes subjected to pulsed electron beam heating in vacuum

A numerical solution for the transient temperature distribution in a cylindrical disc heated on its top surface by a circular source is presented. A finite difference form of the governing equations is solved by the Alternating Direction Implicit (ADI) time marching scheme. This solution has direct applications in analyzing transient electron beam heating of target materials as encountered in the prebreakdown current enhancement and consequent breakdown in high voltage vacuum gaps stressed by alternating and pulsed voltages. The solution provides an estimate of the temperature for pulsed electron beam heating and the size of thermally activated microparticles originating from anode hot spots. The calculated results for a typical 45kV (a.c.) electron beam of radius 2.5 micron indicate that the temperature of such spots can reach melting point and could give rise to microparticles which could initiate breakdown.

Alternating current conduction and impedance spectroscopy analysis on pulsed excimer laser ablated (Pb, La)TiO3 thin films

Lanthanum doped lead titanate (PLT) thin films were identified as the most potential candidates for the pyroelectric and memory applications. PLT thin films were deposited on Pt coated Si by excimer laser ablation technique. The polarization behavior of PLT thin films has been studied over a temperature range of 300 K to 550 K. A universal power law relation was brought into picture to explain the frequency dependence of ac conductivity. At higher frequency region ac conductivity of PLT thin films become temperature independent. The temperature dependence of ac conductivity and the relaxation time is analyzed in detail. The activation energy obtained from the ac conductivity was attributed to the shallow trap controlled space charge conduction in the bulk of the sample. The impedance analysis for PLT thin films were also performed to get insight of the microscopic parameters, like grain, grain boundary, and film-electrode interface etc. The imaginary component of impedance Z" exhibited different peak maxima at different temperatures. Different types of mechanisms were analyzed in detail to explain the dielectric relaxation behavior in the PLT thin films.

Alternating current conduction behavior of excimer laser ablated SrBi2Nb2O9 thin films

Bi-layered Aurivillius compounds prove to be efficient candidates of nonvolatile memories. SrBi2Nb2O9 thin films were deposited by excimer laser ablation at low substrate temperature (400 °C) followed by an ex situ annealing at 750 °C. The polarization hysteresis behavior was confirmed by variation of polarization with the external applied electric field and also verified with capacitance versus voltage characteristics. The measured values of spontaneous and remnant polarizations were, respectively, 9 and 6 μC/cm2 with a coercive field of 90 kV/cm. The measured dielectric constant and dissipation factors at 100 kHz were 220 and 0.02, respectively. The frequency analysis of dielectric and ac conduction properties showed a distribution of relaxation times due to the presence of multiple grain boundaries in the films. The values of activation energies from the dissipation factor and grain interior resistance were found to be 0.9 and 1.3 eV, respectively. The deviation in these values was attributed to the energetic conditions of the grain boundaries and bulk grains. The macroscopic relaxation phenomenon is controlled by the higher resistive component in a film, such as grain boundaries at lower temperatures, which was highlighted in the present article in close relation to interior grain relaxation and conduction properties.

Formation of ferromagnetic clusters in GaAs matrix and GaAs/AlGaAs superlattice through Mn ion implantation at two different temperatures

Different submicron ferromagnets are fabricated into GaAs and GaAs/AlGaAs superlattice through ion implantation at two different temperatures followed by thermal annealing. The structural and magnetic properties of the granular film are studied by an atomic force microscope, X-ray diffraction and alternating gradient magnetometer. By analyzing the saturation magnetization M-s, remanence M-r, coercivity H-c and remanence ratio S-q, it is confirmed that both MnGa and MnAs clusters are formed in the 350degreesC-implanted samples whereas only MnAs clusters are formed in the room-temperature implanted samples. (C) 2004 Elsevier B.V. All rights reserved.