Preparing Interspecific Hybridization in the Genus Lobelia - Nuclear DNA Contents, Pollen Handling, and Localization of Crossing Barriers

摘要

The genus Lobelia is composed of 415 species, which are allocated to 18 sections (LAMMERS 2011). Among the numerous species of the genus, Lobelia erinus hybrids have a very high ornamental value. Breeding has resulted in cultivars with colours as white, pink, lavender, purple and blue, while the red colour is missing. Therefore, possibilities for interspecific hybridization with red-flowering species such as L. gerardii and L. cardinalis were explored to produce a novel red-flowering type of L. erinus hybrids. In a first step DNA content and ploidy level in 39 L. erinus genotypes and 9 other Lobelia species were estimated using flow cytometry and chromosome countings in selected examples. In the L. erinus types tetraploid cultivars had DNA contents of 2.24-2.96 pg 2C(-1), and triploid genotypes 1.78-2.11 pg 2C(-1). Secondly, pollen viability was determined by in vitro pollen germination tests and revealed percentages of 39.1-84.7 % for different selected genotypes, but only 0.5-7.8 % for triploid L. erinus hybrids. Pollen storage at -20 degrees C is possible for at least 6 months with only slightly decreased viability. Moreover, the pollen tube growth was examined at 24 and 48 h after pollination by aniline blue staining in 59 crossing combinations. In most of the crosses the pollen tubes reached the proximity of the ovules. Thus, crossing barriers in interspecific crosses between different Lobelia species and cultivars can be assumed to be predominantly post-zygotic, although in-growth of pollen tubes through the micropyle has not been observed.