Somatic polyploidy and its consequences for flower coloration and flower morphology in azalea

Flower colour variegation is not only a phenomenon of importance to horticu lture, the phenotype involved is also often used as a scientific model syst em for the study of complex gene regulation processes. In the course of suc h studies on azalea, we observed a correlation between flower colour patter ns, flower morphology and somatic polyploidy. Using high-resolution flow cy tometry of nuclear DNA, the ploidy level was determined in flowers of diffe rent azalea sport families. Sports exhibiting variegated flowers with broad (>7 mm), differently coloured, petal edges (picotee type) proved to be tet raploid in the petal edge but diploid in the rest of the flower tissue. Nei ther flower colour pattern nor ploidy differences are periclinal chimeric i n origin, but seem to be correlated with the topographic location of the ce lls within the flower tissue, i.e. the margin of the petals. The possible r ole of gene dosage effects and cell size involved in the remarkable correla tion between somatic polyploidy, (flavonoid) gene expression and flower mor phology is discussed.