Interpretation of a selection plateau through complex segregation analysis: Euclidean distance index selection for flower colour in the davis population of gerbera

Abstract

Two cycles of recurrent phenotypic selection with a weighted Euclidean distance index based on flower colour were applied to individual plants sampled from the Davis population of gerbera (Gerbera jamesonii H. Bolus ex Hooker). The index (I) included CIELAB (1976) variables hue (H), chroma (C) and value (L). The narrow-sense heritability (h2) for I in cycle 0 was estimated at more than 1.0 by half-sib family means and consequently overestimated the selection response. However, the genetic variance was exhausted after two cycles of selection and genetic correlations among the component traits of the index became increasingly positive. Complex segregation analysis (CSA) of index scores in the Davis population supports a mixed Mendelian model with a completely dominant segregating major gene accounting for 20 per cent of the phenotypic variance. This model estimates h2 =0.9 for I and is discussed as it pertains to the effects of selection on the genetic parameters of the selected population. © 1995 The Genetical Society of Great Britain.