Rio de Janeiro Botanic Garden's Conservation Unit and Seed Desiccation Tolerance Research
Volume 2 Number 9 - November 1997
T. S. Pereira
Rio de Janeiro Botanic Garden's Conservation Unit is responsible for establishing a Plant and Seed Collection Policy based on the Convention on Biological Diversity (CBD) in order to guide future research, education and exhibitions.This policy will provide the guidelines for germplasm exchange rules for Brazilian species.
Due to the high diversity of Brazilian flora there is not sufficient knowledge about seed germination behaviour.This information is relevant for seed management in genebanks, for restoration of disturbed areas and for diversity conservation and the genetic integrity of the vegetation.
While seed exchange with other institutions is reduced in the Botanic Garden, as part of our work in implementing the Convention, we have instead prioritized our seed collection work to enable greater large scale nursery production of native plants for plantations and landscape uses.
Seed germination, storage and desiccation tolerance of tropical tree species is the main line of research at the Seed Laboratory. Lack of knowledge on the germination requirements for tree seed species in the tropics, has led to research into the optimal temperature and light for high germination indexes.Using this knowledge we can compare any storage treatment expressed as a (%) of the best germination.Since the main difficulty in seed research is to get large amount of seed to treat and evaluate during a broad period of time, we have concentrated on a few species from endangered taxonomic groups or systems.Some of the results of our investigations are summarised below.
In order to evaluate the effect of drying seed on the subsequent germination of Virola surinamensis, an Amazonian timber species from the swamp forest, seeds were submitted to forced drying (fan) at 50ºC for several time periods (minutes) and stored in polyethylene bags.The results showed that viability was maintained after desiccation from 0 to 120 minutes, being higher at 60 minutes.The best treatment after four months was the control one, where seeds were kept inside water, in plastic bags, confirming the traditional experience of the field worker and overcoming the characteristics of recalcitrant seed (Cunha et al., 1992).
Research on the Sugar Palm (Euterpe edulis Mart.) conducted at the Seed Laboratory, verified that the best conservation results were attained under 15øC (Andrade et al., 1996).If seed moisture could be maintained between 40% and 43%, high values of germination and vigour could be yielded.However, the spontaneous germination within storage plastic bags under 15ºC and 43% seed moisture content suggests the use of partial dehydration (40%) before seed storage to achieve better conservation.Since the Rio Botanic Garden Palm Collection is one of the largest in America, these results could be applied to other palm species.
The majority of tropical tree species have exhibited different levels of desiccation sensitivity (Chin & Roberts, 1980; Normah et al., 1997; Motete et al., 1997).For this reason many experiments are needed to guarantee the best environmental storage conditions to maintain seed integrity over time.Different levels of sensitivity to dessication have been shown in our studies. Many of the species from the Atlantic Rain Forest showed an intermediate to tolerant behaviour, mainly those from the early forest succession.This could indicate that they can be dried and stored under low temperatures. An example of this is Astronium glaziovii (Anacardiaceae), which demonstrates high germination when dried either under silica or ventilation containers (Pereira, unpublished).
In order to evaluate viability x longevity from the soil seed bank, seeds of the pioneer Rapanea ferruginea were stored inside the forest floor and inside the clearing floor, the control treatment were stored under 5ºC.The results demonstrate that the soil seed bank from the forest floor maintained viable (70% germination) after 570 days.This information is being used for the management of the species in deforested lands.
Another example of sensitivity to intermediate desiccation is from seeds of Eugenia brasiliensis, a forest tree fruit species, which has been under investigation in the last 200 days (Andrade et al, unpublished).Preliminary results show that seeds are not tolerant to low temperatures (5ºC), but with a small increase in temperature (10ºC), seed viability (100%) is maintained with 40 to 50% water content when seeds are stored within sealed plastic bags.But are those seeds recalcitrant indeed? Only research will indicate the way to store them.
With these examples we are acquiring knowledge to deal with the requirements of some key species under storage, which will help their management either fresh or desiccated to through different conservation methods for genebank storage.