2018 ASHS Annual Conference

Althea (Hibiscus syriacus) is an ornamental shrub prized for its winter hardiness and large, colorful flowers. Altheas are primarily tetraploids (2n = 4x = 80), although breeders have developed hexaploid and octoploid cytotypes. Although floral traits are most important for breeders of althea, little is known about their segregation patterns. The objectives of this study were to determine segregation patterns in eyespot presence, flower color, and flower form. Over four years, thousands of flowering seedlings were observed representing F₁, F₂, and backcross families. Based on our results, we propose that eyespot presence is controlled by a single locus and that a recessive allele called spotless results in a complete elimination of color. The gene controlling spotless is likely located upstream in the flavonoid biosynthetic pathway. We also propose that flowers with white to blush-pink petal body color and a red eyespot are controlled by a single recessive allele called geisha. This trait exhibits incomplete dominance and is under epistatic control by spotless. It is likely located downstream in the delphinidin biosynthetic pathway, responsible for lavender, dark pink, and blue pigments. In addition to color segregation, depth of color irrespective of hue (CIE L*) was also investigated (spotless and geisha seedlings removed). The deepest pigments were measured in crosses among hexaploid ‘Pink Giant’, taxa homozygous dominant for geisha, and taxa heterozygous for geisha. Conversely, the lightest pigments were observed in crosses between taxa homozygous recessive for geisha and taxa heterozygous for geisha. Future efforts at eliminating the geisha allele from a breeding population may allow for quantitative improvement in total anthocyanin production. Observations on petal number inheritance revealed that seedlings produced a continuous distribution of petal numbers between the petal numbers of the two parents, with occasional transgressive segregants. The highest average petal numbers were found in seedlings resulting from the cross of double-flowered taxa. Flower size (petal area), varied significantly among cross combinations and flower forms. The largest petals were observed in the seedlings of single-flowered by double-flowered crosses. Concomitant upregulation or expression of genes controlling laminar growth in stamen may not only result in petaloid stamen, but may also result in increased laminar growth in the true petals, resulting in wider, overlapping petals. However, further work must be undertaken to eliminate environmental effects on flower size estimates.