Quantitative genetics of floral characters in homostylous Turnera ulmifolia var. angustifolia Willd. (Turneraceae)

Abstract

The genetic basis of floral variation influencing the mating system of Jamaican populations of homostylous Turnera ulmifolia var. angustifolia was investigated using controlled crosses and open-pollinated families. Crosses between plants with large differences in stigma-anther separation and analysis of F2 and backcross generations gave unimodal distributions for all floral characters. No evidence for major gene control of floral variation was obtained and results were contrary to expectations based on segregation at the distyly locus. These data and the continuous distribution of phenotypes among populations indicate that variation is polygenically controlled. Generation means from a cross between plants exhibiting extreme differences in stigma-anther separation could be accounted for by simple biometrical models. An additive-dominance model explained variation in style length while addition of a digenic epistatic parameter was required to account for variation in stamen length and stigma-anther separation. Estimation of repeatabilities and broad-sense heritability indicated genetic variation for style length, stamen length and stigma-anther separation within populations. No genetic correlation was evident for style and stamen length suggesting that selection acting on the mating system of homostylous populations would yield a response.