Introduction
In ornamentals, interspecific breeding is considered to be the most important source of genetic variation. The introgression of genes may be part of a breeding program towards disease resistance, better growth vigor, winter hardiness or morphological alteration in general. Both sexual and asexual hybridization, by pollination and protoplast fusion respectively, are fit to induce the desired introgression into the acceptor species. However, the number of possible barriers is very high (Eeckhaut et al. 2006). The creation of interspecific hybrids, along with chromosome doubling technology, offers extended opportunities for ornamental breeders (Van Tuyl and Kim 2003), as demonstrated in many genera (Kobayashi et al. 2004; Sujatha and Prabakaran 2003; Van Huylenbroeck et al. 2004). Interspecific and even intersubgeneric hybridizations are highly interesting to combine desired traits from genetically distinct genotypes (Van Huylenbroeck and Van Laere 2008; Van Tuyl 1997). Attempts to create interspecific hybrids between H. syriacus and H. rosa-sinensis, especially to introduce new flower colors and forms, were not successful so far (Paek et al. 1989; Yu et al. 1976). However, some interspecific breeding work involving more tropical species of Hibiscus is published (Kuwada 1964; Tachibana 1958).
Geographically, Hibiscus is mainly distributed in tropical and subtropical zones, with some species extending into the temperate regions of the world like; H. syriacus L. (althea or rose of Sharon) and H. sinosyriacus Bailey (Bates 1965). The similarity in natural distribution pattern of these species is an indication of a similar tolerance to environmental factors (Bates 1965). Among them, H. syriacus, a deciduous shrub with more or less distinctly trilobate leaves, is the most popular one. Breeding work is mainly done in this species. The color of the solitary flowers in the axils on the young wood varies from white, light pink or red to purple and blue, generally with a large crimson splash at the base of the petals. Single, semi-double and double blooms are known (Kim and Lee 1991; Yu and Yeam 1987). Flowering time is from the end of July till the first part of October (Bean 1973; Kim and Lee 1991; Krüssmann 1962). Basic chromosome number of H. syriacus is x = 20 and most cultivars are tetraploid, 2n = 4x = 80 (Skovsted 1941). H. sinosyriacus, 2n = 4x = 80 (Skovsted 1941), has broader leaves compared to H. syriacus. The leaves have short triangular lobes and the involucratal bracts outside the calyx are as long as the calyx or even longer (Bates 1965).
In this study, at temps were made to develop new Hibiscus cultivars with vigorous growth, upright, compact branches, and unique flower shape through interspecific hybridization between H. sinosyriacus and H. syriacus. More specific, the aim was to introgress increased growth vigor into H. syriacus by interspecific hybridization with H. sinosyriacus.
Description and Performance
Origin
The breeding program which produced Hibiscus hybrid ‘Woolred’ extended over a period of some 8 years. The objective of the breeding program was to develop new Hibiscus cultivars with vigorous growth and unique flower shape through interspecific hybridization between H. syriacus and H. sinosyriacus.
The new Hibiscus plant developed after cross-pollination between H. sinosyriacus ‘Seobong’ introduced from Belgium, as the female or seed parent and H. syriacus ‘Samchully’ (Plant patent number 1481) as the male, or pollen parent. For the cross H. sinosyriacus ‘Seobong’ × H. syriacus ‘Samchully’, in total 50 flowers were pollinated. The crosses resulted in 32 fruits (64.0% successful pollinations) which contained on average 4.5 seeds. Of the obtained seedlings 115 could be planted in the greenhouse. 87 F1 seedlings of H. sinosyriacus ‘Seobong’ × H. syriacus ‘Samchully’ transplanted in the field and then flowered in 2003. The new Hibiscus hybrid ‘R-161’ was discovered and selected in August, 2004 as a vigorous plant with in the progeny of the stated cross-pollination in anoutdoor nursery environment in the Research Institute of Rose of Sharon and Tiger Lily, Chonan, Korea. Asexual reproduction of the new Hibiscus hybrid ‘R-161’ by hardwood grafting and softwood cuttings in a controlled greenhouse environment since the spring of 2004 has shown that the unique features of this new Hibiscus plant are stable and reproduced true to type in successive generations of asexual reproduction (Fig. 1). After the plant characteristics evaluation such as growth characteristics, leaf shape, leaf size, flower characteristics, and flowering for 3 years (2007 ~ 2009), it was named as ‘Woolred’ in 2010. The characteristics were evaluated based on the manual for agricultural investigation and guidelines for the conduct of tests for distinctness, uniformity and stability for Hibiscus (UPOV 2005).
Description
Plants of ‘Woolred’ had vigorous growth, and upright branches with abundant production of violet-pink (N74C) (Royal Horticultural Society Flower Council of Holland 2001) flowers of moderate size (10 ~ 11 cm) with a violet-pink, red eye spot at the base of each petal, which was visible from a distance (Fig. 2).
The ‘Woolred’ was a vigorous and tall sized plant with upright branches. 5-year-old plant of ‘Woolred’ was 260 cm in height and 180 cm in crown width, and 1-year-old grafted plant was 75 cm in height and 50 cm in crown width (Table 1). ‘Woolred’ was more vigorous compared to H. sinosyriacus. Fig. 2 showed the overall appearance of the new Hibiscus, showing the colors as true as it was reasonably possible to obtain in colored reproductions of this type. Colors in the photographs might differ slightly from the color values cited in the detailed botanical description which accurately described the colors of the new Hibiscus × ‘Woolred’ (Fig. 2). This cultivar was very fertile with abundant seed pods produced from insect pollination.
Leaves were alternate and oval shape (Table 2). The leaf apex was acute, and the base of the leaf was shallowly acute. Leaf margins were irregularly dentate. The leaves were 7.7 cm long and 4.2 cm wide. They were medium to darkgreen in color. The intensity of the green coloring depended upon the nitrogen nutrition of the plant. The new ‘Woolred’ in well grown plants attained a diameter of leaf shoulder of 2.3 cm and a petiole of 1.7 cm. The flower diameter of Hibiscus × ‘Woolred’ was 10.5 ~ 11.5 cm and similarly as compared with contrastive cultivar, ‘Samchully’. The corolla was composed of five slightly fan type of petals, 6.3 cm long by 4.5 cm at the widest point. The petals were violet pink (N74C) (Table 3, 4). The red eye spot was slightly darker red (53A) in color for 3.2 cm (Table 3, 4). A stout staminal column protruded from the central petal attachment that measured 3.3 cm long (Table 5). It beared numerous short-stalked yellow stamens along the basal two-thirds then became bare for about 1.2 cm before terminating into five stigmatic branches, each terminating in a capitate stigmatic lobe. In color, the column shaded from light yellow (NN155C), at the base to cream (154D), at the stigmatic lobes. The pistil protruded from the tip of the anther column before separating into five styles, each 0.5 cm long (Table 5).
Upon anthesis in the early morning, the flower petals reflexed, then gradually returned to nearly right angles to the central axis and remained thus for the life of the flower (Table 4, 6). Hibiscus ‘Woolred’ started to flower each year in early July and continued for about four months, depending upon environmental conditions. The flowering of ‘Woolred’ initiated on July 12 and then total blooming duration was 86 days in Chonan, Korea. The plants then produced sporadic flowering until frost (Table 6).
The stiff, upright main stems of H. × ‘Woolred’ apparently were derived from H. syriacus. It seemed to be increased for vigorous growth into H. syriacus by interspecific hybridization with H. sinosyriacus. The flower color in Hibiscus × ‘Woolred’ was intermediate between the flower colors of H. sinosyriacus ‘Seobong’ and H. syriacus ‘Samchully’. In pose, the flowers of H. × ‘Woolred’ somewhat resembled those of the species H. sinosyriacus in that the flowers expanded their petals widely.
The oval three-lobed leaves of Hibiscus × ‘Woolred’ also resembled those of H. sinosyriacus in shape. H. sinosyriacus was allied to H. syriacus, but had broader leaves, with three short triangular lobes (Bates 1965; Bean 1973).
Plants of the new Hibiscus were more vigorous than plants of the cultivar ‘Seobong’. Hibiscus × ‘Woolred’ differed primarily from plants of ‘Seobong’ in growth habit and flower size as plants of the new Hibiscus were more vigorous and had larger flowers than parent plants. ‘Woolred’ differed from plants of the female and male parents in leaf size and flower color as plants of the parents had smaller and lighter pinkcolored flowers.
Notes for Production
The new Hibiscus × ‘Woolred’ plant grows in well-drained soil. It easily grows in average and medium moisture in full sun to part shade. Best flowering occurs in full sun. It prefers moist, organically rich soils, but tolerates poor soils and some drought. It is very tolerant of summer heat and humidity. Prune to shape in spring. Pruning back to 2-3 buds in late winter may produce larger blooms. It is easily propagated by stem cuttings. May be grown from seed, but seedlings may not have the exact same flower color as the parent. Use a fertilizer that includes trace elements or iron, copper and boron. Perform all pruning in late winter, during the plant's dormant period.
Availability
An application was filed for variety protection of ‘Woolred’ at the Korea Seed and Variety Service (Application no. 2010- 151) and the plant variety protection rights have been registered as grant number 3702 on August 30, 2011. Additional information or a list of nurseries propagating ‘Woolred’ is available on written request to Research Institute of Rose of Sharon and Tiger Lily (RIRS & TL), Chonan, Korea (e-mail: Shimkk@chol.com). In addition, specimens of the releases have been deposited in the Research Institute of Rose of Sharon and Tiger Lily where it will be available for research purposes. The cultivar had been already released by RIRS & TL, Chonan, Korea and has been selling as commercial variety for domestic market.
