Does One Seed Collection Represent the Genetic Diversity of a Population? A Seed Harvest Study

Two genotypes of seeds with different seed coat colour. Similar to morphological polymorphisms, differences in flowering time may depend on differences in genetic composition.

This project is one of a series in the theme of Genetics and Chemical Traits.

The MSB project aims at storing 10% of the world’s dryland species by 2010. The aim is to have at least one copy of 95% of the alleles occurring in the population at frequencies greater than 0.05 represented in all collections. This goal can be achieved by randomly sampling 30 individuals in a completely outbreeding sexual species or 59 individuals in a species with self-fertilisation. Seeds are usually collected at the height of seed maturity on a single collecting trip, thus maximising the seed numbers harvested before dispersal. For obvious reasons this collecting protocol does not cover sub-populations with early or late seed maturation. Depending on the variation in maturation time this may result in a smaller coverage of the genetic diversity than desired.

Multiple studies have shown that there is a strong genetic basis for flowering time. In most species flowering time is a quantitative trait controlled by multiple loci, and seems highly correlated with seed ripening time. As a consequence of differences in flowering time assortative mating can occur, which means that early flowering plants are significantly more likely to mate with other early flowering plants than would be assumed under random mating. Assortative mating results in temporal differentiation of allele frequencies in a population and is especially important for traits closely related to flowering time. This temporal genetic structuring may lead to plants being locally adapted, not only spatially but also temporally. Changed allele frequencies throughout the season may result in reduced genetic diversity and loss of fitness in the population.

In the current project we aim to analyse genetic diversity in a small range of species with different breeding systems, to see if the seed collecting sampling protocols when applied to these species cover the aspired fraction of all alleles in the population. Prairie species are studied since these are under threat by rangeland development. Two species in the Asteraceae family that are common prairie plants have been identified as suitable: Echinacea angustifolia and Penstemon digitalis; a third species will be determined. Microsatellites from related species were demonstrated to amplify in mentioned species; their diversity is currently unknown and needs investigation.

The following questions will be addressed: 1) Do seeds from early, peak and late flowering/harvest times diverge genetically? 2) Is there a significant difference in inbreeding rates between early, peak and late harvesting times? 3) Does assortative mating occur due to asynchronous flowering times? 4) Are there quantitative genetic differences among plants grown from seeds collected at early, peak and late harvest times?

This project started in 2005 and will continue to 2007, results will be written up in a PhD thesis and peer-reviewed publications.

Project Team

Project Leader: Toorop, Peter

Seed Conservation Department

 Peter Toorop, (Dario Prada), Hugh Pritchard

Project Partners and Collaborators

USA

Chicago Botanic Garden

Funders

UK

MSB project

USA

Chicago Botanic Garden, gift in kind