Genetic Variability in Medicago lupulina L. across a Valley in the Weka Pass, New Zealand

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Abstract
Seed was harvested from plants of Medicago lupina L. from ten sites on a transect across a small valley in the Weka Pass, New Zealand. The transect ran from the top of the shady slope to the top of the sunny slope and included marked variation in topography and soil moisture. Approximately ten plants were taken from each site, and twenty seedlings from each plant were raised in boxes and transplanted to the field in a randomised block layout. Flowering time and mean weight per seed were recorded for each plant. There were no significant differences between sites in mean flowering time or seed weight, indicating that no genetic differentiation had taken place for these characters. This was in contrast to an earlier study of flowering time which, when re-analysed showed the between-localities component to be a major contributor to total variance, where populations were collected from widely scattered localities in the South Island of New Zealand. Total variances for flowering time were higher for sites from the bottom of the valley but variances for seed weight were randomly distributed. The lack of genetic differentiation between sites was attributed to lowered selection pressure because of erratic spring and summer rainfall, the long time over which plants can produce flowers, and a gene pool which is kept mixed by seed and pollen dispersal, and buffered by variable seed dormancy.