Inheritance of Leaf Characteristics and Effects of Shading on Growth of Coleus Cultivars and Progenies

Coleus has become an important landscape plant due to their tolerance to heavy rain and high temperature. Various leaf colors and variegations make hybridization breeding of great potential. Differential responses to irradiance exist in coleus and shading could affect leaf color in some cultivars. To investigate the genotypes of cultivars would facilitate coleus breeding. Information of growth responses to shading in cultivars is essential for landscape uses. Thus, the objectives of this study were 1) to determine the leaf genotypes from the phenotype segregations of cross progenies, and 2) to investigate the effects of shading on growth and ornamental quality of coleus cultivars and cross progenies.
For crossing between cultivars, the parents were seed-propagated coleus ‘Wizard Mosaic’ and vegetatively-propagated coleus ‘Black Cloud’, ‘Green Cloud’, ‘The Line’, ‘Defiance’, and ‘Cardinal’. In this study, 16 cross combinations were obtained, with eight reciprocal crosses. Average seed per capsule was two and average seed formation rate per capsule was between 26.6% - 70%, except significantly lower number of seed per capsule in ‘The Line’ (♀) × ‘Black Cloud’ (♂). Seed germination percentage of most cross combinations could reach 76%, except significantly lower germination in reciprocal crosses of ‘Black Cloud’ and ‘Green Cloud’. The seed germination percentage could reach 100% in crosses of ‘Black Cloud’ (♀) × ‘The Line’ (♂), and ‘Defiance’ (♀) × ‘The Line’ (♂).
We determined leaf characteristic genotypes of parents by crossing between cultivars. According to the references, deep lobed margin, crinkled surface, and anastomosis vein of ‘Black Cloud’ and ‘Green Cloud’ were all dominant types, so the expected genotypes were L_, C_, and G_, respectively. Shallow lobed margin, smooth surface, and regular vein of ‘The Line’, ‘Defiance’, ‘Cardinal’, and ‘Wizard Mosaic’ were all recessive types, so the genotypes should be ll, cc, and gg, respectively. Progenies from reciprocal crosses of ‘Black Cloud’ and ‘Green Cloud’ had both dominant and recessive phenotypes. Thus, the genotypes of two cultivars should be Ll, Cc, and Gg. The leaf margin, surface, and vein genotypes of parents were all recessive, with genotypes of ll, cc, and gg in ‘The Line’, ‘Defiance’, ‘Cardinal’, and ‘Wizard Mosaic’, and the phenotypes of reciprocal progenies were also all recessive. Genotype of leaf with pattern variegation included pp and ppm, when the only one solid green genotype which relative to pattern genotype (pp or ppm) was pmpm. Leaf color of reciprocal progenies from ‘Defiance’ and ‘Cardinal’ expressed as pattern and solid green. Thus, the pattern genotype of ‘Defiance’ and ‘Cardinal’ should be ppm, and the genotype of solid green progenies should be pmpm.
Five seed-propagated cultivars, five vegetatively-propagated cultivars, and ten cross progenies were grown under 0% (765 μmol•m-2•s-1 PPF), 48% (398 μmol•m-2•s-1 PPF), and 67% (252 μmol•m-2•s-1 PPF) shading in greenhouse conditions for 37 days. Except 97-6, a progeny between seed-propagated and vegetatively-propagated cultivar, all other progenies were hybrid between vegetatively-propagated coleus cultivars. Seed-propagated coleus cultivars had higher plant height, wider leaves, fewer new grown leaves, bigger total leaf area, and lower dry mass under 67% shading level. Seed-propagated coleus cultivars under 0% shading level were short, with small new grown leaves and poor quality. Seed-propagated coleus cultivars under 48% shading had better growth performance than under 0% or 67% shading levels. Growth responses of vegetatively-propagated cultivars to shading were not so significant as seed-propagated coleus cultivars. Except cross progeny 97-9, growth under various shadings did not differ significantly in cross progenies from vegetatively-propagated coleus cultivars. The vegetatively-propagated coleus cultivars or progenies had wider adaptability to shading than seed-propagated coleus cultivars. In general, the crossing progenies between vegetatively-propagated and seed-propagated coleus cultivars had wider light adaptability than seed-propagated coleus cultivars. When under 0% shading level, the green leaf portions of commercial cultivars and cross progenies were lighter, while the red leaf portions were darker. In contrast, when under 67% shading level, the green leaf portions of leaves of commercial cultivars and cross progenies were dark-green, while the red portions were brighter.