Plant Science London Field Course – Part 2

At the Millennium Seed Bank vault (image: Eoin Lettice)

Day Two by Bianca Govi (APB3)

Today we took a trip to Sussex to complete our tour of Kew by visiting Wakehurst Place. The site is unique in that it houses in-situ and ex-situ conservation efforts, and boasts the highest living plant biodiversity in the world. This latter claim concerns the Millennium Seed Bank, an active seed library of non-crop species, providing an insurance policy against extinction as well as education and research opportunities. The facility, which was inaugurated in 2000 and currently holds 82000 separate collections, has the goal of storing 25% of the world’s floral biodiversity by 2020.

the goal of storing 25% of the world’s floral biodiversity by 2020

Although the seeds preserved in the vault are not directly economic crops, human benefit is one of the strategic priority of the project. A significant example of how this can be achieved is through the storage and study of the genetic diversity of crops’ wild relatives, for future introgression breeding. At the moment, research in this area is focusing on wild rice species Oryza nivara, O. officinalis and O. longistaminata, and wild bananas Musa accuminata and M. balbisiana. Other target priorities in the selection of the new entries include criteria of endangerment and endemism.

UK Seed Hub entrance (image: Bianca Govi)

Seed material -ideally with accompanying herbarium samples- arrives to Kew from 170 partner institutions from 80 different countries, under the convention of Biological Diversity. Once in Wakehurst, seed parcels are stored in a dry room (at 15% relative humidity and 15°C) under a constant, controlled airflow for up to 6 months, to decrease moisture content. We were shown how samples are then taken to a cleaning laboratory, where material is cleaned and sorted manually, through sieves, aspirators and scanned in a medical X-ray machine. For this last step, a subset of 50 seeds is analysed, and the internal integrity of the contents used to estimate germination potential for the whole collection. After the cleaning, seeds are taken into the vault basement where they undergo further drying, are packed, and finally stored in one of the 4 cold rooms (-20°C). Although there is a high degree of variability between species, it had been estimated that the average seed’s lifespan can be increased by 50% for every 1% reduction in ambient relative moisture and 5°C drop in temperature. In general, conditions of low temperature and low humidity slow down seed aging by dampening the release and activity of reactive oxygen species within the tissues. This is unfortunately not true for “recalcitrant” seeds, which do not tolerate drying and storage.

Millennium Seed Bank glasshouse (image: Eoin Lettice)

Commonly, they are large-sized seeds (acorns, chestnuts, giant coconuts), but also some very small ones such as orchid micro-seeds can suffer from substantial drops in germination rates after desiccation. In contrast, some seeds have been observed to maintain their viability even under non-optimal condition. In the succulents’ glasshouse we had the chance to see a 10-year old potted Leucospermum, an African flowering shrub, with an adventurous life history. It was brought to Kew as a seed from the National Archives, where it had been sitting inside the leather-bound notebook of a Dutch merchant who had collected it around the Cape of Good Hope some 200 years previous.

After the tour of the building, we stepped outside, past the parterres representing natural habitats in a gradient from shore shingles, to grasslands, to heath, to bog land, and into the UK Native Seed Hub propagation field. This initiative initiative was launched to address the issue of habitat fragmentation and impoverishment and its goal is to provide the starting stock of seed material for native habitat restoration projects. Special attention is given to rare and difficult to propagate species, which are not widely available from commercial providers. At the moment the field is being used to propagate calcareous soil wildflowers, a particularly niche and threatened community. The area, which is open to the public during the summer, is decorated with willow and wire sculptures.

Millennium Seed Bank (image: Bianca Govi)

Finally we had a brief tour of the Wakehurst Gardens: developed by Gerald Loder, were donated by the following owner to the National Trust and are now managed by Kew. The plant collection features rare exotic entries such as the extinct-in-the-wild Franklin tree and the endangered Wollemia pine, which seems to do particularly well on the local soil. Native woodland protected areas are also part of the estate, making Wakehurst the first botanic garden to also incorporate in-situ conservation operations.

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