Do recalcitrant seeds really exist?

Abstract

-(Do recalcitrant seeds really exist?). In the 70's, seeds were divided into two categories: recalcitrant and orthodox. In the 80's, it was necessary to create an intermediate category; from the 90's onwards, a gradient between orthodox and recalcitrant categories has been considered by several authors. Currently, the terms orthodox and recalcitrant are appropriate just for technological purposes, not for scientific studies. It seems that the differences between recalcitrant and orthodox seeds lie only on the maturity stage in which they are detached from the mother plant, the recalcitrant ones in a very immature stage. This implies that little progress should be expected to expand the storability of these recalcitrant seeds with the application of any treatment after harvesting. Efforts shall be focused on amplifying the maturation period of these seeds by keeping them linked to the mother plant until the maturation process has been completed. Key words: conservation, desiccation tolerance, maturation, seed storage RESUMO -(Sementes recalcitrantes realmente existem?). Na década de 1970, as sementes foram divididas em recalcitrantes e ortodoxas. Na década de 1980, foi necessário criar a categoria das intermediárias e, a partir de 1990, um gradiente entre as categorias ortodoxas e recalcitrantes tem sido considerado por vários autores. Atualmente, os termos ortodoxa e recalcitrante são apropriados apenas para fins tecnológicos, não para estudos científicos. As diferenças entre sementes recalcitrantes e ortodoxas parecem residir apenas no estádio de maturidade no qual se desprendem da planta mãe, as recalcitrantes em uma fase muito imatura. Isso implica que pouco progresso deve ser esperado para expandir a capacidade de armazenamento com a aplicação de qualquer tipo de tratamento após a colheita dessas sementes recalcitrantes. Esforços devem ser voltados para ampliar o período de maturidade das sementes, mantendo-as ligadas à planta-mãe até que o processo de maturação tenha sido concluído. Palavras-chave: armazenamento, conservação, maturação, tolerância à dessecação

Viability of Brazilwood seeds (Caesalpinia echinata Lam.) stored at room temperature in controlled atmospheres

“…Among the different flasks with salt solution, as expected, the seed water content was lower for the lower RH, reaching values of less than 6% in silica and in ZnCl 2 . However, even in these concentrations the germination was greater than 30% (Table 3), confirming the desiccation tolerance in seeds of C. echinata (Barbedo et al, 2002). Also confirmed was the low storage capacity of the seeds of this species in a nonrefrigerated environment (Mello et al, 2013) because even with very low WC there was reduction in the germination and in the values of germinated seeds; the longer the period of storage, the lower the germinability (Table 3).…”

“…After collection, the seeds were transported to Laboratório de Sementes do Instituto de Botânica (Seed Laboratory of the Botanical Institute) (23°37' S, 46°32' W, altitude 798 m), in the city of São Paulo, where they were processed by eliminating cracked seeds or the ones infested by insects, but maintaining the control of the origin. After this selection, the seeds were dried to approximately 10% water content -WC (wet basis), in an oven at 40 °C (Barbedo et al, 2002). They were then stored in a freezer at -18 °C (Hellmann et al, 2006;Mello et al, 2013) until the beginning of the experiments, not exceeding seven days of the date of collection.…”

“…Seeds that issued primary root with at least 1 cm were used to calculate the percentage of germinated seeds; those resulting in the development of normal seedlings (Barbedo et al, 2002) were used to calculate the percentage of germination.…”

“…However, the lack of basic knowledge about the behavior of seeds in many forest species, mainly the ones native from Brazil, hampers the use of this conservation strategy (Pilatti et al, 2011). It is known that the conservation of Caesalpinia echinata Lam., Brazilwood, for example, requires sub-zero temperatures (Hellmann et al, 2006), but the factors that lead to loss the viability of these seeds in less than 60 days when stored at or close to the ambient temperature are not known (Barbedo et al, 2002). This is a species that, in addition to its historical importance to Brazil and being one of the most important flora currently at risk of extinction and of its economic and pharmacological potential (Pilatti et al, 2011;Lamarca and Barbedo, 2012;Cruz-Silva et al, 2013;Gomes et al, 2014), produces seeds of great scientific interest because they are tolerant to desiccation, but with low storage capacity.…”

“…Brazilwood seeds have an orthodox behavior and can maintain viability for up to 18 months when stored at 7 °C (Barbedo et al, 2002) and up to five years at -18 °C (Mello et al, 2013), at water content of about 10% in both cases. However, studies are inconclusive with regard to the storage of these seeds at room temperature, hindering the use of this low-cost way of storage (Lamarca and Barbedo, 2012).…”