Floral variation in Saxifraga granulata: Phenotypic selection, quantitative genetics and predicted response to selection

Plants of Saxifraga granulata, derived from a factorial crossing experiment, were raised under seminatural conditions (garden) to determine whether style morphology and other floral traits were heritable and correlated with female pollination efficiency (seed-set per flower). Differences between paternal half-sib families were statistically significant for most characters with low to moderate narrow-sense heritabilities for flower number, flowering date, plant height, petal size, stamen length and seed-set (h(2)=0.03-0.54) and high heritabilities for style length and stigma size (h(2)>0.75). In addition to a major trend contrasting early flowering, tall, many-flowered genotypes with large flowers and those with the opposite features, there was a strong negative genetic correlation between stamen length and stigma size. Seed-set per flower was highest for early flowering plants with many flowers, tall stems and large stigmas, and increased by 120 per cent after hand-pollination. Only flowering date had a direct effect on seed-set, whereas other traits were associated with seed-set through general plant vigour. Genetic responses predicted from selection coefficients, heritabilities and genetic correlations indicated a shift towards increased plant height, flower number, style length and stigma size and earlier flowering date.