Tratamentos para superação da dormência das sementes de capim-braquiária cultivar Marandu

Abstract

RESUMO -Com o objetivo de verificar a eficiência de diversos tratamentos para superar a dormência das sementes de capim-braquiária foi instalado um experimento com três lotes de sementes do cultivar Marandu. Para tanto, as sementes foram submetidas a diferentes tratamentos que consistiram na remoção manual dos envoltórios (glumas), embebição das sementes em substrato umedecido com nitrato de potássio (KNO 3 ) a 0,2%, imersão das sementes em ácido sulfúrico (H 2 SO 4 ) concentrado por 15 minutos e utilização de diferentes períodos de envelhecimento acelerado e a testemunha. No envelhecimento acelerado, as sementes foram submetidas à temperatura de 43 o C, por diferentes períodos de exposição (12, 24, 36, 48, 60 e 72 horas). As características avaliadas nas sementes foram a germinação, a viabilidade pelo teste de tetrazólio, a pureza física, o grau de umidade e a massa de mil sementes. Os resultados foram submetidos à análise de variância e de regressão para avaliação dos diferentes períodos de envelhecimento. Na comparação dos diferentes tratamentos com a testemunha foi utilizado o teste de Dunnett, a 5% de significância. A remoção das glumas das sementes é um tratamento eficiente na superação da dormência das sementes de capim-braquiária cultivar Marandu. O envelhecimento acelerado é um método capaz de superar a dormência das sementes de capim-braquiária cultivar Marandu, contudo o período de exposição pode variar conforme a qualidade inicial do lote.Termos para indexação: Brachiaria brizantha, ácido sulfúrico, nitrato de potássio, germinação.TREATMENTS TO OVERCOME Brachiaria brizantia SEED DORMANCY ABSTRACT -An experiment was performed with three commercial seed lots of Marandu cultivar to evaluate the efficiency of several treatments to overcome Brachiaria brizantha seed dormancy. The seeds were submitted to different treatments which consisted of individually hand-dehulled seed, caryopsis imbibition in substrate soaked with potassium nitrate (KNO 3 ) solution at 0.2% concentration, seed scarification with concentrated sulphuric acid (H 2 SO 4 ) for 15 minutes, different periods of accelerated aging and the control. The accelerated aging test consisted of six periods of exposure (12, 24, 36, 48, 60 and 72 hours) to a temperature of 43 o C. The evaluated characteristics were seed germination percentage, viability through the tetrazolium test, seed purity percentage, moisture content and the weight of one thousand seeds. The results were submitted to variance and regression analysis to evaluate the different accelerated aging periods. The different treatments were compared with the control using the Dunnett test, at 5% probability. The individually hand-dehulled seed was considered the best treatment to overcome physiological seed dormancy. The accelerated aging test was an effective treatment to release B. brizantha seed dormancy, however the exposition period was variable with the initial seed quality of the seed lot.

Physiological changes in hybrid Brachiaria cv. Mulato II after accelerated aging to overcome dormancy

“…For the scarified seeds, seeds without chiseling had lower electrical conductivity values and these values decrease linearly until the end of the exposure time of the seeds to the accelerated aging. That is evidencing a probable cellular repair, in accordance with the results obtained by authors such as Vieira and Silva and Barros (1998), Martins and Silva (2003), Meschede et al (2004), Previero et al (1998), Santos et al (2011), working with other Brachiaria species.…”

“…In seeds of U. brizantha cv. Marandu, a similar effect was observed by Custódio et al (2012), who emphasize that seed dormancy in Brachiaria species is caused by different factors, which may occur in isolation or in combination (Meschede et al, 2004;Alves, 2008, Gaspar-Oliveira et al, 2008;Sallum et al, 2010).…”

“…Due to the importance of forage species, it is relevant to improve the technologies to add higher quality seeds, which has a direct relationship with pasture formation, thus ensuring a faster response to the investments made in the production process (Martins and Silva, 2003;Meschede et al, 2004;Quadros et al, 2012).…”

<b>Priming and stress under high humidity and temperature on the physiological quality of <i>Brachiaria brizantha</i> cv. MG-5 seeds

“…However, Cardoso et al (2014) observed that increasing periods of aging (stress at high humidity and temperature) positively influenced dormancy breaking, which was also verified by Meschede et al (2004). However, these authors also highlighted that this effect depends on the physiological quality of the initial lot because aging (stress at high humidity and temperature) can break physical dormancy in non-scarified B. brizantha seeds.…”

“…MG-5. Meschede, Sales, Braccini, Scapim and Schuab (2004) reported that dormancy can be overcome by artificial aging, but the results depend on the physiological quality of the seed lot. However, this practice can expose the seeds to conditions that reduce their physiological potential .…”