Thermal and moisture content effects on storability and seed dormancy releasing on Brachiaria brizantha cultivars

Abstract

-Brachiaria species normally show a double seed dormancy mechanism, mainly on fresh-harvested seeds, leading to germination percentages lower than those of viability detected by tetrazolium test (TZ) and causing problems as to storage, trading and seed inspection activities. The adoption of the methodology to detect the constants of the viability equation (high storage temperatures and fixed moisture contents) made feasible in this research to isolate the effects of 40, 50 and 65°C on B. brizantha cultivars Marandu, Mulato 1 and Mulato 2 seed dormancy releasing, after storage with moisture contents ranging from 1.9 and 17.8%. Seed samples presented high dormancy levels, detected by TZ and it was complete and partially released by chemical scarification and accelerated ageing test, respectively. No statistical differences were observed as to the speed of germination (T 50 ); however, differences among cultivars were detected as to number of seed per gram. Sorption and desorption isotherm curves were similar for the cultivars. Seed dormancy releasing was better achieved at 40 and 50°C with mc ranging from 7.6 to 10.8%. The temperature of 50°C appears to be adequate for seed dormancy releasing in all mc analyzed. No significant seed dormancy releasing result was observed at 65°C. The cultivar Marandu presented the highest storability throughout the experiment.Index terms: activity of water, seed longevity, high storage temperatures. EFEITOS TÉRMICOS E DE GRAUS DE UMIDADE NA ARMAZENABILIDADE E NA LIBERAÇÃO DA DORMÊNCIA DE SEMENTES EM CULTIVARES DE Brachiaria brizanthaRESUMO -As espécies do gênero Brachiaria apresentam mecanismo duplo de dormência de sementes, principalmente nas recém colhidas, resultando em porcentagens de germinação inferiores às de viabilidade detectadas pelo teste de tetrazólio (TZ), causando deste modo problemas com relação ao armazenamento, comercialização e fiscalização do comércio. A metodologia para determinar as constantes da equação de viabilidade (altas temperaturas e graus de umidade constantes) mostrou-se eficiente nesta pesquisa para isolar os efeitos de temperaturas de 40, 50 e 65°C na liberação da dormência de sementes de B. brizantha dos cultivares Marandu, Mulato 1 e Mulato 2, após armazenamento com graus de umidade variando de 1,9 a 17,8%. As amostras de sementes apresentaram altos níveis de dormência, que foram detectadas pelo TZ e completa ou parcialmente liberada através da escarificação química e do teste de envelhecimento acelerado, respectivamente. As isotermas de sorção e desorção foram similares para os cultivares. A liberação da dormência foi mais bem sucedida a 40 e 50°C com graus de umidade variando de 7,6 to 10,8%. A temperatura de 50°C parece ser a mais adequada para a liberação da dormência em todos os graus de umidade analisados. Não foi observada uma liberação da dormência das sementes significativa a 65°C. O cultivar Marandu apresentou a maior armazenabilidade durante todo o experimento.Termos para indexação: atividade de água, longevidade de sementes, al...

Seed quality parameters of three interspecific hybrids of elephant grass x pearl millet

“…By the test of mass of 1,000 seeds and by purity analysis, performed in the work samples, approximately 147,000 pure seed kg -1 were obtained for hybrid Paraiso and 311,000 pure seeds kg -1 were obtained for hybrid Pastoreio. Such variations on values of this quality parameter were also observed by Cavalcante-Filho and Usberti (2008) in different cultivars of Brachiaria brizantha and other tropical grasses.…”

Predicting the impact of increasing carbon dioxide concentration and temperature on seed germination and seedling establishment of African grasses in Brazilian Cerrado

“…These results are normal for the genus Urochloa and especially for U. brizantha , which has low germination due to the phenomenon of dormancy and thus produces poor uniformity in germination thereof (Garcia & Cícero ; Vieira et al . ; Martins & Silva ; Cavalcante‐Filho & Usberti ). The most common causes of seed dormancy in this species are the physiological immaturity of the embryo and wrap impermeability to water (Garcia & Cícero ).…”

“…These results are normal for the genus Urochloa and especially for U. brizantha, which has low germination due to the phenomenon of dormancy and thus produces poor uniformity in germination thereof (Garcia & Cícero 1992;Vieira et al 1998;Martins & Silva 2001;Cavalcante-Filho & Usberti 2008). These results are normal for the genus Urochloa and especially for U. brizantha, which has low germination due to the phenomenon of dormancy and thus produces poor uniformity in germination thereof (Garcia & Cícero 1992;Vieira et al 1998;Martins & Silva 2001;Cavalcante-Filho & Usberti 2008).…”

“…In the specific case of U. brizantha, Vieira et al (1998) showed that storage temperature affects seed dormancy behaviour of this species and that a temperature of 28°C accelerated overcoming seed dormancy in relation to other temperatures tested. Also, elevated storage temperatures such as 65 and 70°C before germinating could overcome dormancy and enhance seed germination (Vieira et al 1998;Martins & Silva 2001;Cavalcante-Filho & Usberti 2008) and germination rate of U. brizantha (Martins & Silva 2001). All seeds used in this work were stored at room temperature before germination tests, but as shown by germination percentage presented by U. brizantha under control treatment, room temperature did not reach 28°C.…”

Accelerated aging for evaluation of vigor in Brachiaria brizantha ‘Xaraés’ seeds

“…Accelerated aging at 43 ºC for 48 h was used by Dias et al (2004) to monitor the physiological quality of Brachiaria brizantha cv Marandu seeds during storage. Cavalcante-Filho and Usberti (2008) used accelerated aging to break the dormancy of B. brizantha cv Marandu seeds and Mulato 1 and Mulato 2 hybrids. These authors concluded that the temperature of 43 °C for 72 h was effective in breaking dormancy.…”