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Seed banks susceptible to sham samples

March 11, 2011 By Virginia VG Gewin This article courtesy of Nature News.

Genetic analysis calls into question the authenticity of older cultivars in seed collections.

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Seed banks are meant to preserve biodiversity for the future. Some house centuries-old cultivars, which remain valuable to plant breeders trying to develop seeds with unique combinations of traits. But a study published this week in Crop Science1 reveals that a surprising number of banked samples may be incorrectly identified.

Mark van de Wouw, a biologist at the Centre for Genetic Resources in Wageningen, the Netherlands, and his colleagues made a genetic analysis of 360 unique lettuce-seed samples marked with the same name, and revealed that almost one-quarter were wrongly labelled. The oldest seeds had the most mistakes: samples of cultivars stored before 1900 had only a 56% chance of being named correctly, whereas those stored between 1960 and 1989 proved almost 90% authentic.

Errors can occur during seed handling or through cross contamination when regenerating seeds, but van de Wouw found that most errors occurred during the initial labelling of the seed. And in the past, growers were less exact about the names given to plant varieties, so even labels written correctly at the time may be wrong according to modern standards.

"History is carried into the gene bank — all the errors of the past are still there," says van de Wouw. He was prompted to carry out the study as a result of frustrating experiences with mislabelled samples in the course of his own research. Once, for example, he requested a vetch seed from a seed bank and was sent a pea seed.

The problem is well recognized in seed-bank circles, but this is the first time it has been systematically analysed. "The thing that worries many of us in the seed-bank community is when users simply take the name on trust without performing a taxonomic analysis to validate what they have," says Michael Way, head of collecting at the Millennium Seed Bank in West Sussex, UK, which is run by the Royal Botanic Gardens at Kew.

Improved protocols

Charlotte Lusty oversees efforts to conserve seed collections for the Global Crop Diversity Trust in Rome. She agrees that there is an urgent need to make sure that collections are what they are meant to be, but points out that the study demonstrates how much modern seed banking has improved. Lusty says that the standards and protocols for labelling or regenerating a seed, put in place under the direction of the Food and Agricultural Organization of the United Nations in 1994, are now working well to properly maintain collection integrity. "Modern gene banks aren't the same as they were 50 years ago," she says.

Well-financed seed banks, such as those overseen by the US Department of Agriculture, have multiple strategies to safeguard collections. For example, at the National Center for Genetic Resources Preservation in Fort Collins, Colorado, which houses more than 875,000 plant samples, crop-specific curators work solely to obtain new material and validate its authenticity. Pictures of samples are taken when cultivars are added to the bank, and databases prevent workers entering taxonomic data that is misspelled or not already in the system, says David Dierig, research leader at the centre.

It will be easier to check the authenticity of older collections as genotyping costs decrease, but other checks can also be helpful. For example, Biodiversity International in Rome, which is devoted to conserving agricultural biodiversity, is responsible for a large collection of banana plantlets maintained in test tubes. In 2006, when they grew the collection out, they found that some samples were not recognizable as the named variety, and others had changed as a result of mutations during storage. It is a time and resource intensive check, but a valuable validation exercise. "That type of ground-truthing is going on now at the gene banks that have labour and resources to spare," says Jeremy Cherfas, spokesman for Biodiversity International.

But for the majority of seed banks, simply keeping collections going is a struggle, says Lusty. Most aren't that well funded, and with few resources they focus on their main priority: keeping thousands of seeds viable under proper conditions

Authentication is particularly crucial for samples to be sent to the Svalbard Global Seed Vault, or Doomsday Vault, located on a remote Norwegian island near the North Pole. Regional seed banks around the world are responsible for selecting and validating the viability of seeds to be stored at the vault, which exists only as a back-up in case of widespread data loss. Inaccurate labelling there could lead to total loss of information.

Van de Wouw hopes that his paper will encourage seed-bank managers to make every possible effort to maintain the integrity of past and future collections. "In any case, seed-bank users should check to make sure what they get is what they wanted — especially among older cultivars," he says.

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