Dormancy release and germination in recalcitrant Aesculus hippocastanum seeds

The investigation of dormancy release in Aesculus hippocastanum seeds was aimed at estimating the proportion of coat-imposed to embryo dormancy, and studying the growth initiation providing embryo dormancy release. During winter, horse chestnut seeds exhibited 16–17 week-lasting deep dormancy, which predominantly was determined by coat-imposed dormancy. Embryo dormancy lasted for 11–12 weeks of wet cold stratification. Embryo dormancy was weak, even the embryo axes excised from deeply dormant seeds were capable of extending to the size exceeding the axis length in intact seeds at radicle protrusion. Embryo dormancy release manifested itself in gradually increasing growth capacity of both embryo axes and cotyledonary petioles. The growth initiation in horse chestnut seeds occurs only by cell elongation. During growth initiation, a more rapid fresh weight gain was observed in comparison with length increment, thus indicating that accumulation of osmotically active substances and active water uptake by embryo axis cells were ahead of their increasing longitudinal cell wall extensibility. Cell wall loosening appeared to be directly related to embryo dormancy release. The hormonal regulation of embryo dormancy release in horse chestnut seeds is discussed

Session 08 Germination and dormancy

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Hidrocondicionamento de Parkia pendula [Benth ex Walp]: sementes com dormência física de árvore da Amazônia Hydropriming of Parkia pendula [Penth. ex Walp.]: seeds with physical dormancy from Amazon tree

O visgueiro é uma árvore neotropical de importâncias econômica e ecológica. Este estudo objetivou determinar o tempo de embebição e o teor de água de sementes de Parkia pendula necessários para ativar o metabolismo e aumentar o desempenho pelo condicionamento. Sementes armazenadas (2 anos) e não armazenadas (7 dias) foram comparadas. Após o desponte as sementes foram submersas em água a 15 ºC, por períodos de 4 a 28 h, para atingir o grau de embebição desejado (20, 40, 60, 80 e 90%). Em seguida, foram diretamente semeadas em areia lavada no viveiro (4 x 25 sementes/tratamento) ou dessecadas durante sete dias (24±2 °C e 68±3% UR) antes da semeadura. Sementes não armazenadas e sem condicionamento (controle) apresentaram 59±8,9% de emergência, valor inferior ao daquelas armazenadas e sem condicionamento (76±11,3%). Períodos de submersão superiores a 13 h reduziram o desempenho da germinação em relação às sementes não condicionadas. Porém, após 4 h (26-31% de teor de água das sementes) ambas as sementes não armazenadas e armazenadas aumentaram o desempenho, sendo, ainda, maior quando houve dessecamento após a submersão. Portanto, os efeitos positivos do condicionamento ocorreram na fase I da curva de embebição. O hidrocondicionamento de 4 h a 15 ºC mostrou ser uma opção econômica e de fácil aplicação em sementes de P. pendula: aumentou a velocidade do desenvolvimento das plântulas, a porcentagem de germinação das sementes não armazenadas em níveis similares aos das armazenadas e a sincronização da germinação em sementes armazenadas.<br>Visgueiro is a neo-tropical tree species with economic and ecologic importance. This work aimed to determine the imbibition time and moisture content of P. pendula seeds necessary to activate metabolism and improve their performance by priming. Stored seeds (2 years) and unstored seeds (7 days) were compared. After clipping, the seeds were kept in water at 15 ºC for periods of 4 to 28 hours to reach the desired imbibition degrees (20, 40, 60, 80 and 90%). Seeds were then sown immediately in washed sand in the nursery (4 x 25 seeds / treatment) or dried for 7 days (24±2°C and 68±3% R.H.). Unstored and unprimed (control) seeds showed 59±8.9% germination, which was less than that of stored unprimed seeds (76±11.3 %). Submersion periods exceeding 13 hours reduced germination relative to unprimed seeds. After 4 hours of submersion (seed moisture 26-31%), both unstored and stored seeds increased their performance. Even higher improvement was verified when drying followed submersion. Thus, the positive effects of priming occurred in phase I of the imbibition curve. Hydropriming of 4 hours at 15 ºC was found to be a simple and inexpensive method for P. pendula seeds since it increased seedling development velocity, brought the germination percentage of unstored seeds to a level similar to that of stored seeds and increased germination synchronization of stored seeds