Background and aims: Petals are important for Primula sieboldii because of the commercial value of its flowers, and their form is a target characteristic for breeding. An appropriate understanding of petal form in terms of genetic mechanisms and environmental effects is necessary for improvement of this species. The aim of this study was to establish a quantitative evaluation method of petal shape by elliptic Fourier descriptors and principal component analysis (EF-PCA), and thus to investigate genotypic and environmental effects on petal morphology.
Methods: EF-PCA describes an overall shape mathematically by transforming coordinate information concerning its contours into elliptic Fourier descriptors (EFDs) and summarizing the EFDs by principal component analysis. To examine varietal effects on principal component (PC) scores and petal area among commercial varieties, nested ANOVAs were performed (since the samples had a hierarchical structure with four sources, i.e. variety, plant, flower and petal).
Key results: Petal shape variation could be evaluated successfully and the symmetrical and asymmetrical elements of the overall shape variation could be detected. The proportions of the variance component due to varietal differences were more than 70 % in the first five PCs of the symmetrical elements and petal area. By contrast, the proportions due to varietal effects of all PCs of the asymmetrical elements were less than 20 %, and the proportions of the variation within a flower were more than 75 %. It was also demonstrated that the yearly variance of petal shape was small, and that of petal area was large.
Conclusions: Within a flower the major source of the symmetrical elements is genotypic and the asymmetrical elements are strongly affected by the environment. With respect to petal area, the contribution of genotypes is also large; it is, however, affected by the macro-environment more notably than is petal shape.