Superação da dormência de sementes de capim-carrapicho Dormancy overcoming in southern sandbur seeds

O objetivo desta pesquisa foi o de identificar tratamentos que, capazes de superar a dormência das sementes de Cenchrus echinatus, fossem favorá veis à germinação e passíveis de serem aplicados visando semeadura à campo. Para tanto, 4 lotes de sementes foram submetidos a tratamentos de escarificação mecânica, de retirada do invólucro de brácteas espinhosas e das glumas para a separa ção da cariopse , de imer são em KNO3 (1%) por 5 e 20 minuto s, imer sã o em KNO3 (1, 3 e 5%) por 5 minutos, de imersão em H2O por 5 minutos, de armazenamento a 5°C/ 7 dias, de exposição à 40, 55 e 70°C/ 8h em estufa com circulação forçada de ar e de imersão em H2SO4 (98%, 36N) por 1; 5 e 15 minutos seguida por lavagem em água co rren te. As sementes tratadas foram avaliadas por meio dos testes de germinação e de emergência de plântulas; de primeira contagem de germinação e de emergência de plântulas, de velocidade germinação e de emergência. Os tratamentos de escarificação mecânic a, da cariopse nua e de imersão das sementes em KNO3 (1 a 3%) por 5 minutos são técnicas de superação da dormência capazes de implementar a emergência em condições de campo.<br>The main goal of this research was to identify those treatments that besides being capable of overcoming dormancy in Cenchrus echinatus seeds were favorable to germination and liable to field use. Four seed lots were submitted to mechanical escarafication, cariopse excised, KNO3 (1%) immers ion fo r 5 and 20 minutes, KNO3 (1, 3 e 5%) immersion for 5 minutes, H2O immers ion for 5 minute s, 5°C/7 days storage, thermal treatments at 40, 55,and 70°C/8h in air circulating oven, H2SO4 (98%, 36N) immersion fo r 1, 5, and 15 minutes. Treated seeds were evaluated by means of the standard germination test and emerging seedlings, first germination and emergence count, germination and emergence speed. The use of mechanical escarafication, cariopse excised, KNO3 (1 - 3%) immersion for 5 minutes are dormancy overcoming techniques able to promote field emergence

Cryopreservation of Seeds and Seed Embryos in Orthodox-, Intermediate-, and Recalcitrant-Seeded Species

Seeds are one of the preferable and most used sources of germplasm for the ex situ preservation of plant genetic resources. They are generally stored dry at -20 °C in seed banks following international standards. However, some seeds do not tolerate drying and/or storage at -20 °C, or present short lifespans at these conditions. For them cryopreservation is indicated for long-term preservation. When seeds tolerate desiccation (i.e., orthodox seeds), they can be dried at about 32 ± 3% relative humidity at 18 °C and stored in the vapor phase of liquid nitrogen. This is the method followed in the Millennium Seed Bank of the Royal Botanic Gardens, Kew, for wild species with short lifespans in the standard conditions of seed banks. When seeds do not tolerate desiccation (i.e., recalcitrant seeds) or their tolerance to desiccation and/or -20 °C storage is limited (i.e., intermediate seeds), drying and cooling procedures must be adjusted, and often, cryoprotection is also required. Some methods are detailed for diverse species of temperate and tropical origin