With restricted populations and a small number of individuals, Discocactus bahiensisBritton & Rose (Cactaceae) is an endangered species in Brazil and its capacity for the formation of seed banks in the soil and the maintenance of seed viability remains unknown. Thus, the aim of the present study was to determine the most efficient way to maintain viability during storage of seeds of D. bahiensis. Seeds were stored in paper bags and either kept in a cold chamber (7 AE 2 C) in the dark (ex situ conservation) or buried in the soil to a depth of 5 cm in an area of natural occurrence of the species (in situ conservation). Germinability of the seed banks was evaluated monthly for 20 months. During the first 10 months of storage, germinability of the seeds conserved in situ and ex situ was similar to that of recently collected seeds. After this period, a 70% reduction in germinability was found for the seeds maintained in situ and there was nearly complete loss of viability after 12 months of storage in the field (germinability < 10% in the last 8 months of the experiment), indicating the ability to form persistent soil seed banks. In contrast, the seeds stored in the cold chamber maintained greater than 70% germinability throughout the entire analysis period, demonstrating that ex situ conservation is the most efficient way to maintain the viability of the seeds of this endangered species.
Temperature, light, water availability and excessive salt in the soil are among the abiotic factors that most influence the germination process in semiarid ecosystems. The aim of the present study was to determine the effect of these abiotic factors on seed germination in three subspecies of cactus: Discocactus bahiensis, D. zehntneri subsp. petr-halfarii and D. zehntneri subsp. zehntneri. Seeds were set for germination under two light conditions (12-h light/dark photoperiod and continuous darkness) and 10 temperature treatments [eight constant temperatures (10, 15, 20, 25, 30, 35, 40 and 45 °C) and two alternating temperatures (30 to 20 °C and 35 to 25 °C)]. Polyethylene Glycol (PEG) 6000 and sodium chloride (NaCl) were used to simulate water and saline stress, respectively, with the following osmotic potentials: 0.0, -0.2, -0.4, -0.6, -0.8 and -1.0 MPa. Three subspecies were positive photoblastic. The optimum temperature for germination was 25 to 35 ºC for D. bahiensis and D. zehntneri subsp. zehntneri, and 30 to 35 ºC for D. zehntneri subsp. petr-halfarii. The seeds of all three subspecies exhibited tolerance to water and saline stress, as germination was observed at potentials for up to -0.6 MPa in the PEG and NaCl solutions.
resumo -Embora sejam publicados artigos sobre sementes de cactos dos diversos ecossistemas brasileiros há mais de 50 anos, as pesquisas que envolvem o conhecimento acerca da morfologia e fisiologia das sementes e plântulas de Cactaceae são consideradas extremamente recentes no país, pois, durante as quatro primeiras décadas, muito pouco foi publicado sobre essa temática. No Brasil são encontradas 262 espécies de cactos que se distribuem por todo território nacional, porém, até o final da década de 1990, apenas cinco espécies tinham sido estudadas. Dessa forma, o objetivo do presente estudo foi realizar uma revisão bibliográfica para mostrar os avanços nos estudos sobre sementes e plântulas de cactos do Brasil, desde a primeira publicação em 1966 até a presente data. Para atender os objetivos propostos neste estudo, uma extensa revisão bibliográfica foi realizada para a busca de publicações sobre três temas principais: (1) morfologia e anatomia de sementes e plântulas, (2) comportamento germinativo e fatores bióticos e abióticos que afetam a germinação e (3) desenvolvimento inicial e sobrevivência de plântulas de espécies de cactos do Brasil. Nas últimas cinco décadas, 81 artigos sobre esses três temas foram publicados com espécies de cactos que ocorrem no Brasil. Entretanto, a grande maioria desses estudos é recente, sendo que 68% desses artigos foram publicados de 2010 a 2017. O tema mais estudado foi o efeito dos fatores abióticos na germinação das sementes. Apenas 71 espécies foram estudadas até o momento e alguns padrões já podem ser apontados como, por exemplo, o fotoblastismo positivo da subfamília Cactoideae. Finalmente, incentiva-se a realização de mais estudos sobre essas temáticas, principalmente com representantes da família Cactaceae que ocorrem nos ecossistemas com menor número de espécies estudadas, como o Pampa e o Pantanal. pAlAvrAs-chAve: Revisão BiBliogRáfica; cactaceae; MoRfologia; geRMinação; cResciMento inicial. AdvAnces in studies on seeds And seedlings of brAziliAn cActiAbstrAct -Although papers about cacti seeds from different Brazilian ecosystems have been published for more than 50 years, research involving the knowledge about the morphology and physiology of Cactaceae seeds and seedlings is considered extremely recent in the country because during the first four decades, few papers have been published about this topic. In Brazil, 262 species of cacti are found that are distributed throughout the national territory, but until the end of the 1990s, only five species had been studied. Thus, the aim of the present study was to carry out a bibliographic review to show the advances in the studies on seeds and seedlings of cacti from Brazil, from the first publication in 1966 to the present date. In order to accomplish the objectives proposed in this study, an extensive bibliographical review was conducted to search for publications on three main topics: (1) morphology and anatomy of seeds and seedlings, (2) germinative behavior and biotic and abiotic factors affecting seed germination and (3...
This study evaluates the effects of hydration and dehydration cycles (HD cycles) on seed germination of four Caatinga tree species (Anadenanthera colubrina var. cebil, Enterolobium contortisiliquum, Pityrocarpa moniliformis and Pterogyne nitens) subjected to different temperatures and determine the thermal upper and lower limits of germination. For this, seeds were subjected to 0, 1, 2 and 3 HD cycles and set to germinate at temperatures of 5, 10, 15, 25, 35, 40 and 45 °C. Germinability and t50 were calculated and the differences of these parameters were compared by two-way ANOVA. In addition, germination rate (GR = 1/t50), as well as ceiling (Tc), optimum (To) and base (Tb) temperatures were calculated to estimate the limits below or above which the seeds fail to germinate. We observed that the more HD cycles, the better the seed responds, especially at extreme temperatures. Seeds of all studied species showed To between 25 and 35 °C, Tb < 10 °C, and Tc > 40 °C. The slope of regression curves for germination rate showed that submitting seeds to HD cycles expands its thermal tolerance range, revealing that this seed pre-treatment can be efficient for species as it increases their tolerance to thermal stress.
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