Abstract
We investigated the flower characteristics of interspecific hybrids between Spiraea thunbergii Sieb. ex Blume. and S. japonica L. fil. via ovule culture. The flower bud differentiation of hybrid plants started in December and the flower cluster formation started in February, then flowered in the middle of April. The flowering period of hybrid plants was 2 months from April to May, which was the intermediate between S. thunbergii and S. japonica. In hybrid plants and S. japonica, the flower setting was observed in the terminal of a current shoot elongated in the present year. Although the inflorescence of S. thunbergii was the unbel type, that of hybrid plants and S. japonica showed the corymb type. In the hybrid plants, the size of style, the number of stamen and the number of flowers per one inflorescence showed intermediate values between S. thunbergii and S. japonica. The color of petals in S. japonica was deep pink or red, while the hybrid plants had pink petals. Total anthocyanin concentration in petals of the hybrid plant was lower than that of S. japonica. Six types of anthocyanin (Cy3Ga, Cy3G, Cy3Ara, Pg3G, Mv3G, unknown) were detected in the petals of S. japonica, and the hybrid plant had four cyanidin pigments (Cy3Ga, Cy3G, Cy3Ara, Unknown) among six anthocyanins contained in S. japonica petals. The amounts of Pg3G and Mv3G seem to cause changes in the petal hue of S. japonica and hybrid plants. Furthermore, the fading of petals in the hybrid plant through flower senescence was caused by the marked decrease of Cy3Ga, which was one of main anthocyanin in hybrid plant.
