Segregation of Flower Color and Eyespot in Althea

Abstract

Althea (Hibiscus syriacus) is an ornamental shrub prized for its winterhardiness, flower colors, and unique flower forms, including single-flowered and double-flowered types. Although floral traits are most important for breeders of althea, little is known about their segregation patterns. The objective of this study was to determine segregation patterns in flower color, including eyespot, among hybrid seedlings of elite taxa. Over 4 years, more than 3100 flowering seedlings were produced for observation of F1, F2, and backcross families. For each plant, data were collected including presence of eyespot and petal body color (CIEL*a*b*) using a colorimeter. Recessive testcrosses and χ2 analyses were performed among three taxa (‘Buddha Belly’, ‘Diana’, and White Chiffon®), and between this recessive group and a suite of colorful taxa. Self-pollination and intercrosses within homozygous dominant and homozygous recessive groups further confirmed their genotypes. Based on these results, we propose that eyespot is controlled by a single gene called spotless, named for the recessive allele that results in a complete elimination of color in flowers. Crosses that resulted in seedlings that all produced eyespots were observed to segregate for color in the petal body. Of these, one group produced white to blush pink petals, which was recessive to full color. Recessive testcrosses and χ2 analyses were performed among nine taxa exhibiting eyespots with white to blush petal bodies, and between taxa with full-color petal bodies. These testcrosses resulted in a putative homozygous dominant group composed mostly of blue and dark pink taxa, whereas the heterozygous group was composed mostly of pink taxa. Spotless taxa were also added to these two groups, suggesting an epistatic interaction with the spotless allele. Based on these results, we propose that petal body color is controlled by a single gene called geisha, named for the recessive allele that produces white to blush-pink petal bodies and dark red eyespot. This trait exhibits incomplete dominance and is under epistatic control by spotless. Geisha-type flowers lack pigment in the petal body, or exhibit a blush pink, likely produced by low levels of cyanidin, peonidin, and pelargonidin. The interaction and segregation of these two genes was confirmed in F1, F2, and backcross families from two crosses: Lil’ Kim™ × Blue Chiffon™ and Fiji™ × White Chiffon®. This study on segregation of flower color in H. syriacus contributes substantial and useful information on inheritance of color and will facilitate targeted breeding to improve this vibrant ornamental shrub.