Seed mass, genotype, and density effects on growth and yield of Oenothera biennis L.

Seed mass and genotypic effects on the growth and reproduction of Oenothera biennis L. over a gradient of intraspecific density were examined in a greenhouse experiment. By using genetically identical seeds from five parental genotypes we were able to examine independently the effects of seed mass and genotype on seedling and adult performance. Seedling size was significantly correlated with seed mass for the first five weeks but had no effect on adult size or reproductive output. In contrast, genotype differences became increasingly apparent with time. In particular, there were striking differences in reproductive output among genotypes. Plants grown from two of the genotypes consistently produced more, but lighter, seeds and a greater proportion flowered at high density than the other three genotypes. In all five genotypes, seed number was much more variable than seed mass across the density gradient. Initial seed mass accounted for a significant proportion of the variation in progeny seed mass, and mean seed mass produced in the greenhouse was positively correlated with mean seed mass of the parent (in the field). This result, together with the observed constancy of seed mass within a genotype across the density gradient, indicates the differences in reproductive output among these genotypes are genetically determined.