BREEDING OF AUTUMN-FLOWERING INTERSPECIFIC HYBRIDS OF ALLIUM

Interspecific hybrids between Rakkyo (Allium chinense G. Don) and its relative species, A. thunbergii G. Don and A. virgunculae var. kiiense Murata, were produced by an ovary culture. Among these hybrids, two cultivars being suitable for cut flowers and one cultivar for pot flowers were selected. The cultivars for cut flowers bloomed from late October to early November. They had solid stems between 50 and 70 cm in length with little tight spherical umbels from 5 to 6 cm in diameter consisting of more than 80 florets with six reddish purple petals. They produced two to three bulbs from one plant per year. The pot-flower cultivar also bloomed in October and had thin but solid stems of about 25 cm in length with small and spherical umbels of 3 cm in diameter consisting of more than 40 florets with six reddish purple petals. They produced three bulbs from one plant per year. In addition, all these cultivars were easy to cultivate. The new cultivars from interspecific hybrids of Allium reported here can create a new demand for cut flowers and pot flowers because of their autumn-flowering character without competing with other ornamental Allium species which flower in spring to early summer. INTRODUCTION There are a lot of commercial varieties of ornamental Allium species, but many of them are selected from wild types. Limited breeding of ornamental Allium species has been conducted. Most of the ornamental Allium bloom from spring to summer (Stearn, 1986). However, A. chninense, which is grown in Japan as a vegetable and some wild types of the species bloom in autumn. Though A. chinense does not have seed fertility because of autopolyploidy (Nishitani, 1980), some other Allium species in Japan are fertile. The Allium species in Japan are too small or too poor in quality to be used as cut flowers as they are. That is why we tried the first interspecific hybridization between commercial ornamental Allium and autumn-flowering Japanese Allium species. Consequently, some hybrids were obtained but all of them bloomed in summer (Nomura et al., 2002). On the other hand, Dubouzet et al. (1993) reported that hybrid plants between A. chinense and A. thunbergii were suitable for ornamental cut flowers. So next we tried a hybridization between A. chinense and A. thunbergii. It made a new cultivar of autumn-flowering Allium named ‘Autumn Violet’ (Nomura et al., 2001). This cultivar was between 50 and 60 cm tall and had reddish purple spherical umbels of 6 cm in diameter. It started to bloom in late October. However, this cultivar had a fault in that the flowers bloomed simultaneously. Because of this the harvest did not last. That is why we tried to make varieties which flowered both earlier and later than this cultivar. Additionally, we hoped that the subsequent cultivars would have taller and thicker stem with richer umbel. In this study, we made two cut-flower cultivars, which bloomed at different times respectively and were of a higher quality than ‘Autumn Violet’. Moreover a small and pretty pot-flower cultivar was also made. MATERIALS AND METHODS Cross Combinations and Ovary Cultures In making the cut-flower cultivars, ‘Autumn Violet’ was used as a maternal plant Proc. IX Intl. Symp. on Flower Bulbs Eds.: H. Okubo, W.B. Miller and G.A. Chastagner Acta Hort. 673, ISHS 2005 142 and was hybridized with A. thunbergii in October of 1996. The maternal plant was emasculated before the crossing. In making the pot-flower cultivar, A. chinense was used as a maternal plant and was hybridized with A. virgunculae var. kiiense in October of 1997. The emasculation of the maternal plant was not needed because of the pollen sterility of A. chinense. The ovaries of the maternal plants were cultured five days after pollination to preserve the hybrid embryos. After removing petals and pistils, the ovaries were collected and sterilized in 70% (v/v) ethanol for a few seconds and then in 1% (v/v) sodium hypochlorite solution for 10 minutes. Then they were rinsed three times in sterile distilled water. After rinsing, they were placed vertically on an MS (Murashige and Skoog, 1962) medium supplemented with 5% sucrose and solidified with 0.8% agar. The pH of the culture medium was adjusted to 5.8, and the media were autoclaved. The culture was kept at 25°C under white fluorescent light (2000 lx) with a 16-hour photoperiod for two months. The seedlings germinated from the ovaries on the MS medium were transferred to an MS medium containing 3% sucrose and 0.8% agar, which was adjusted to pH 5.8 before autoclaving. Morphological Characteristics of Hybrid Plants The hybrid plantlets were planted in pots from in vitro cultures in the following March and were grown in a greenhouse. In August, the bulbs of the hybrid plants were transplanted into a sand field and were vegetatively propagated. Each year in August, the bulbs were harvested, divided individually and then replanted in the same sand field for propagation. After the propagation, the multiplied bulbs were divided individually and were replanted in the sand field with 30 cm row spacing and 15 cm distance between each bulb in August of 2002. During the next year, the morphological characteristics and growth of each hybrid were investigated in June when the growth was most vigorous. The characteristics of the flowers were examined in October. Twenty plants per cultivar were examined in each stage. RESULTS Cut flower types were selected from the hybrids of ‘Autumn Violet’ and A. thunbergii. ‘Autumn Violet’ was a commercial variety which had already been made from the hybrid of A. chinense and A. thunbergii. A pot-flower type was selected from the hybrids of A. chinense and A. virgunculae var. kiiense. The appearance of these cultivars was similar to that of A. caeruleum or A. cowanii in that they had reddish purple umbels. They were also bulb forming plants. Their important characteristic was their ability to flower in autumn. The early-flowering type of the new cultivars for cut flowers was named ‘Autumn Violet 2’ (Fig. 1 and 2) and the late-flowering type was named ‘Autumn Violet 3’ (Fig. 3). On the whole the plant posture of the new cultivars was similar to that of ‘Autumn Violet’. The plant height, number of leaves and leaf width of ‘Autumn Violet 2’ were respectively 30 cm, 10.6 leaves and 6.4 mm. They were almost the same as those of ‘Autumn Violet’ but the leaf length of ‘Autumn Violet 2’ was 51 cm, which was about 10 cm longer than that of ‘Autumn Violet’ (Table 1). That is why ‘Autumn Violet 2’ looked larger than ‘Autumn Violet’. As for ‘Autumn Violet 3’, the plant height, number of leaves and leaf length were respectively 24 cm, 8.3 leaves and 43 cm. All of these measurements were a little smaller than those of ‘Autumn Violet’. However, the leaf width of ‘Autumn Violet 3’ was 7.1 mm, which was wider than that of ‘Autumn Violet’. The pot-flower was named ‘Autumn Violet Mini’ (Fig. 4) and the plant posture was similar to that of A. virgunculae var. kiiense on the whole. The plant height, leaf length and leaf width of ‘Autumn Violet Mini’ were respectively 20 cm, 28 cm and 3.0 mm which were less than those of ‘Autumn Violet’. But the number of leaves of the ‘Autumn Violet Mini’ was 12.2, which was more than that of ‘Autumn Violet’. That is why the ‘Autumn Violet Mini’ looked smaller than the ‘Autumn Violet’. Concerning the bulb formation of ‘Autumn Violet 2’, it multiplied at a rate of three times each year which was the same as that of ‘Autumn Violet’ (Table 2). The weight of all