A reply to Walck & Dixon from Brian Forde-Lloyd, Nigel Maxted and Luigi Guarino.
In Walck and Dixon’s opinion (Nature 462: 721, 2009) it’s ‘time to future-proof plants in storage’, but how novel and useful is this idea?1 Few would argue with the principle that we need to maximise the range of genetic diversity conserved ex situ, but some of the issues raised need further consideration.
1. Collecting species at the limits of their ranges could be a good idea — this could be where adaptations most likely to be occurring; for wild wheat populations, genes thought to be adaptive to biotic and abiotic stress have been found to be highly variable in some ecological circumstances (e.g. wild wheat in Israel). But, more generally, population genetic theory suggests that genetic diversity will reduced at range margins, where population sizes will be small.
2. Collecting samples every 10 to 20 years may not be long enough for genetic adaptation to be manifested, particularly in perennial species, but equally may not be frequent enough to prevent severe genetic erosion under rapid climate change of annual species.
3. ‘Conditioning’ seeds at high temperature to allow for the selection of genotypes with temperature tolerance will have a seriously adverse effect on genetic diversity as a whole. Regenerating seeds from small numbers followed by their reintroduction will impose a severe genetic bottleneck. On the positive side, evaluating germplasm for adaptation to abiotic stress has certainly been encouraged for many years now by those scientists, genetic conservationists and plant breeders who continue to value and conserve those wild plant species that are relatives of crops.
4. Mixing seed samples to allow ‘cross-breeding’ and then allowing selection to act upon the genetic variation that results is not dissimilar to plant breeding. But is it not just as likely that outbreeding depression rather than the desired heterosis will result? There is a growing opinion amongst plant breeders anyway that conventional plant breeding is too slow a process to keep up with climate change. Also, is it feasible to consider ‘breeding’ is manner suggested all wild species before they are reintroduced to the wild.
5. ‘Conditioning’ and mixing seed sample then replanting them in the wild is likely to result in genetic pollution and potential diluting of local ecotypic adaptation. This has already been shown to occur in species with wild and cultivated components. The niche that any plant grows within is defined by a complex range of biotic and abiotic interactions and not all will be impacted by a changing climate.
6. But here’s the real conundrum, if seed banking (ex situ conservation) is currently inadequate, why not simply rely upon in situ conservation of wild plant species in genetic reserves? It would seem that the arguments that climate change will preclude such an approach in the near future applies equally to the suggestions made in this article.
In the final scheme of things, complementary approaches to the conservation of plant diversity, both ex situ and in situ, are important for that diversity to be used to its fullest, and not just for reintroduction alone. This needs strengthened support in the face of climate change, the scientific case for which has been argued for at least the last 20 years.Footnotes: