RESUMO
Chenopodium hircinum, the putative wild ancestor of quinoa, is a source of traits that could improve the tolerance of crop quinoa to high temperatures. However, seeds of C. hircinum have physiological dormancy (PD), which is an obstacle for plant propagation and use in breeding programs. We studied the intraspecific variability in morpho-anatomical traits of embryo covering structures and their association with PD. We also evaluated the effects of different dormancy-breaking treatments on PD alleviation and germination. Seeds were dispersed with a remnant perianth and a persistent pericarp that could be removed by scraping. The seed coat was formed by palisade cells impregnated with tannins, and the seed contained a thin layer of peripheral endosperm surrounding the embryo. In our investigation, the thickness of the pericarp (P) and/or seed coat (SC) varied among populations. Populations with higher P and/or SC thickness showed lower percentages of germination and water absorption. The combined dormancy-breaking treatment (bleach + perforated coverings + gibberellic acid) promoted dormancy release and increased germination. C. hircinum seeds showed non-deep physiological dormancy. Based on previous knowledge about quinoa, and our results, we conclude that embryo coverings, especially the seed coat, have an important role in dormancy control, imposing a mechanical restraint on radicle emergence.
RESUMO
The persistence of subtropical seasonally dry forests urgently requires the implementation of ex situ conservation and restoration programs. We studied variation in seed traits and dormancy of six native species growing in seasonally dry Chaco forests of Argentina. We documented high intra- and interspecific variability in seed traits and dormancy. Fresh seeds of Geoffroea decorticans and Parasenegalia visco (Fabaceae) were water-permeable and nondormant (ND), while those of Parkinsonia praecox and Vachellia aroma (Fabaceae) were water-impermeable and had physical dormancy (PY). Seeds of Schnopsis lorentzii (Anacardiaceae) and Sarcomphalus mistol (Rhamnaceae) were water-permeable and had physiological dormancy (PD). Mechanical and chemical scarification were the most effective methods to break PY, and dry storage for 3 months was effective in breaking PD. Seeds of large-seeded species were ND or had PD, and those of small-seeded species had PY. Species inhabiting moist habitats had ND seeds, whereas those from seasonally dry habitats had seeds with PY or PD. These results suggest that seed traits and dormancy are species-specific and that intraspecific variation in seed traits is likely associated with high phenotypic plasticity of species in response to local environmental heterogeneity. These findings should be considered at the time of implementation of conservation techniques and for seed sourcing decisions for restoration.
RESUMO
To mitigate anthropogenic impacts on plant diversity in tropical montane grasslands, one of the most threatened ecosystems in Brazil, it will be essential to develop ex situ conservation strategies to preserve wild species. The lack of basic research on the seed storage behaviour of grassland species may, however, limit their use for reintroduction and restoration projects. We investigated seed storage behaviour at the community level by comparing the effects of cold-low RH (10 °C; 10% RH) and freezing-low RH (20 °C; 10% RH) conditions on seed viability, germination and dormancy of 47 species. Fresh seeds of 43% of the species showed primary dormancy. More than half of the species showed high seed survival responses (viability >60%) under both storage temperatures. Despite a variety of dormancy responses among the different species, the low RH storage conditions tested released dormancy for most species during 12- and 30-month storage times. Multivariate analysis of the best (freezing-low RH, 30 months) storage condition evidenced the formation of five distinct groups, three with species having high conservation potential in seed banks. Although further studies are needed to test dormancy-breaking treatments and improve seed conservation practices, this first approach to assessing seed banking techniques could contribute to demand for locally adapted seeds for ecological restoration projects in tropical montane grasslands.
Assuntos
Germinação , Dormência de Plantas , Brasil , Ecossistema , Pradaria , Sementes , TemperaturaRESUMO
PREMISE: Although fire cues (high temperatures and smoke) influence seed germination in numerous species from fire-prone environments, their effects on seed germination of species from neotropical savannas are poorly understood. METHODS: We exposed seeds of eight grass species from the Cerrado, the Brazilian savanna to heat-shock (80°C or 110°C for 5 min) and/or smoke water, and then set them to germinate in light or dark, at either summer (28°C/18°C) or winter (27°C/14°C) temperature regimes in an incubator. In addition, we evaluated the effects of smoke water on seedling root and shoot growth for four of the species. RESULTS: Smoke interacted with the dark treatment to increase germination from 28% to 93% in Aristida recurvata and 77% to 95% in Aristida riparia. Smoke had no effect on germination of either of these species in the light. Heat-shock alone also promoted seed germination in A. recurvata. For Digitaria lehmanniana, smoke interacted with heat-shock to improve germination from 5% to 16%. In contrast, the fire treatments did not have any effect on the seed germination of the remaining five species. Smoke water stimulated root growth for A. riparia, A. recurvata, and Ctenium cirrosum but had no effect on their shoot growth. CONCLUSIONS: The strong promotive effect of smoke on Aristida germination suggests that these species are fire-adapted. Aristida species have an active awn system, which facilitates seed burial, and the smoke and dark interaction would ensure buried seeds germinated post-fire. The species that showed no response to fire cues may either have adapted via alternative strategies or require different concentrations of smoke or levels of heat. This study is one of very few examples showing a positive germination and seedling growth response to smoke for species from neotropical savannas.
Assuntos
Germinação , Plântula , Brasil , Sinais (Psicologia) , Pradaria , Poaceae , SementesRESUMO
Abstract:Ochradenus baccatus is a perennial glycophyte growing in Middle East and it is one of the most important food sources for many animal species in desert regions. The aim of our study was to investigate the effects of seed storage, light, temperature and gibberellic acid (GA3) on germination of O. baccatus seeds. We also investigated the germination characteristics of O. baccatus seeds under different saline concentration and their capability to recover germination once they were transferred to distilled water. Seeds were stored at room temperature (20 ± 2 ºC) and at -18 ºC. Germination tests were conducted at alternating temperatures of 15/25, 20/30 and 25/35 ºC in either continuous darkness or photoperiod of 12-h dark/12-h light. To study the effect of GA3 on germination of O. baccatus seeds, freshly-collected seeds and stored seeds were soaked for 24 h in a GA3 water solution (1 g/L) before sowing. To assess the salinity tolerance during germination, seeds were germinated under different salinity levels (100, 200 and 400 mM NaCl). Stored seeds at room temperature and -18 ºC germinate equally well at different temperature regimes and light conditions. However, freshly matured seeds were not able to germinate even when they were treated with GA3. On the contrary, stored seeds at room temperature and -18 ºC treated with GA3 increase the final germination percentages. These results indicated that O. baccatus seeds have physiological dormancy and they need to be stored in order to break their dormancy. In the present study, one year of storage did not show a significant variation in germination between the two storage conditions assayed. Therefore, further research is needed to know about the maximum storage period for O. baccatus seeds under different storage conditions. Very few O. baccatus seeds (less than 5 %) germinated at the tested lowest concentration of NaCl. However, ungerminated seeds were able to germinate when salinity stress was alleviated. In conclusion, O. baccatus seeds have physiological dormancy, and seed storage (at room temperature and at -18 ºC) for one year is effective for breaking this dormancy. In addition, O. baccatus seeds present ability to remain viable in saline conditions and they will be able to germinate once the salinity level decrease. Rev. Biol. Trop. 64 (3): 965-974. Epub 2016 September 01.
ResumenOchradenus baccatus es un glicófito perenne que crece en oriente Medio y es una de las fuentes de alimentación más importantes para muchas especies animales de regiones desérticas. El objetivo de nuestro estudio fue investigar los efectos del almacenamiento de semillas, luz, temperatura y ácido giberélico (GA3) en la germinación de semillas de O. baccatus. También se ha investigado la germinación de semillas de O. baccatus bajo diferentes concentraciones salinas y su capacidad para recuperar la germinación una vez que fueron transferidas a agua destilada. Las semillas se conservaron a temperatura ambiente (20 ± 2 ºC) y a -18 ºC. Los ensayos de germinación se realizaron a temperaturas alternas de 15/25, 20/30 y 25/35 ºC bajo oscuridad continua o fotoperiodo de 12-h oscuridad/12-h luz. Para estudiar el efecto del GA3 en la germinación de semillas de O. baccatus, semillas recién recolectadas y semillas almacenadas se sumergieron durante 24 h en una solución acuosa de GA3 (1 g/L) antes de la siembra. Para evaluar la tolerancia a la salinidad durante la germinación, la semillas fueron germinadas bajo diferentes niveles de salinidad (100, 200 y 400 mM ClNa). Las semillas conservadas a temperatura ambiente y a -18 ºC germinaron igualmente bien en los diferentes regímenes de temperatura y condiciones de iluminación. Sin embargo, las semillas recién maduradas fueron incapaces de germinar incluso cuando se trataron con GA3. Por el contrario, las semillas almacenadas tratadas con GA3 incrementaron los porcentajes finales de germinación. Estos resultados indican que las semillas de O. baccatus tienen dormición fisiológica y necesitan ser almacenadas para romperla. En este estudio, un año de conservación no supuso una variación significativa en la germinación entre las dos condiciones de conservación ensayadas. Por lo tanto, se precisan investigaciones adicionales para conocer cuáles son los periodos máximos de almacenamiento de semillas de O. baccatus bajo diferentes condiciones de conservación. Muy pocas semillas de O. baccatus (menos del 5 %) germinaron a la concentración más baja de ClNa. Sin embargo, las semillas no germinadas fueron capaces de germinar cuando el estrés salino fue aliviado. En conclusión, las semillas de O. baccatus tienen dormición fisiológica y el almacenamiento de las mismas (a temperatura ambiente y a -18 ºC) durante un año es eficaz para romper dicha dormición. Además, las semillas de O. baccatus presentan capacidad para permanecer viables en condiciones salinas y serán capaces de germinar una vez que el nivel de salinidad disminuya.
Assuntos
Sementes/fisiologia , Temperatura , Germinação/fisiologia , Resedaceae/fisiologia , Dormência de Plantas/fisiologia , Luz , Valores de Referência , Fatores de Tempo , Água/fisiologia , Análise de Variância , Clima Desértico , Ambiente Controlado , Salinidade , Oriente MédioRESUMO
Miconia chartacea es un árbol con amplia distribución altitudinal y latitudinal en Brasil, que se encuentra desde formaciones vegetales estacionales xerofíticas como Caatinga y Cerrado hasta bosques pluviales como Mata Atlántica, en pastizales con árboles aislados hasta interior de bosques maduros. Fue descrita la respuesta germinativa de las semillas de M. chartacea a la luz, temperatura, hormonas vegetales y posmaduración a baja temperatura. Los frutos se recolectaron en la reserva de Cerrado "Prof. Karl Arens", en el municipio Corumbataí (San Paulo, Brasil), la cual presenta una estación seca y fría desde abril hasta septiembre y una estación húmeda y caliente de octubre a marzo. Las semillas se dispersaron durante la estación seca, son fotoblásticas positivas bajo temperaturas constantes y variables, la germinación disminuye bajo irradiaciones de luz blanca inferiores a 17 umol/m2s, la razón rojo/rojo lejano (R/RL) no afectó el porcentaje de germinación, pero la velocidad de germinación aumentó a partir de razones R/ RL > 0.4. Las semillas germinaron en el intervalo térmico de 15 a 35 °C, la temperatura optima esta entre 20 y 25 °C, la alternancia de temperatura no estimuló la germinación respecto a las temperaturas constantes. Las semillas presentaron latencia fisiológica no profunda, la cual fue rota mediante posmaduración durante 93 días a 7 °C y el etileno estimuló la germinación. La gama de temperaturas en la cual germinan las semillas fue menor en las semillas maduradas bajo las condiciones más calientes de la transición de la estación lluviosa a seca que las semillas maduradas en la estación seca. El requerimiento de un periodo frío para romper latencia disminuye la probabilidad de que las semillas germinen durante el invierno, quedando listas para germinar en el verano. Así, la detección de cambios estacionales de temperatura del suelo y el aumento de sensibilidad a la temperatura después de un periodo de frío son responsables por el control temporal de la germinación de M. chartacea, mientras que la respuestas a luz permite que solo germinen las semillas que están en la superficie del suelo, y favorece la germinación en claros de bosque pequeños a grandes.
Miconia chartacea is a widely distributed tree along both altitudinal and latitudinal gradients in Brazil, and it can be found in seasonal xerophytic vegetation, e.g. Caatinga and Cerrado, and tropical rainforest (e.g. Mata Atlantica), from grassland with scattered trees to mature forest. We studied the germination response of M. chartacea seeds to light, temperature, plant hormones and after-ripening at low temperature. Seeds were collected from a Cerrado reserve located in Corumbataí, Sao Paulo State, which characterizes to have a cool dry season from April to September, and a warm wet season from October to March. M. chartacea seeds are dispersed in the dry season and exhibited a photoblastic behavior both at constant and alternating temperatures. The germination was decreased at irradiances below 17 umol / m2s, whereas R: FR ratios below 0.4 reduced the germination rate, but not the germination capacity. The germination-permissive temperatures range from 15 to 35 °C, with an optimum interval from 20 to 25 °C. Germination is not improved by alternating temperature regimes as compared to isothermal treatments. The seeds have a non-deep physiological dormancy, which can be partially overcame either by dry after-ripening at 7 °C for 93 days, or by the 2-chloroethylphosphonic acid treatment. The thermal window within which the seeds germinate was narrower for seeds matured in the rainy to dry season transition period, under warmer conditions, than in the dry season. Cold requirement for dormancy break in seeds of M. chartacea can prevent the germination in the winter, allowing the seeds to germinate in the summer under more favorable conditions. The results suggest that seed response to temperature accounts for temporal distribution of germination, of M. chartacea, while light predominantly influences the spatial distribution of seedlings, precluding the germination of buried seeds and affecting the germination response to gap size.