INTERPRETATION OF A SELECTION PLATEAU THROUGH COMPLEX SEGREGATION ANALYSIS - EUCLIDEAN DISTANCE INDEX SELECTION FOR FLOWER COLOR IN THE DAVIS POPULATION OF GERBERA

Two cycles of recurrent phenotypic selection with a weighted Euclidean distance index based on flower colour were applied to individual plan ts sampled from the Davis population of gerbera (Cerbera jamesonii H. Bolus ex Hooker). The index (I) included CIELAB (1976) variables hue ( H), chroma (C)and value (L). The narrow-sense heritability (h(2)) for I in cycle 0 was estimated at more than 1.0 by half-sib family means a nd consequently overestimated the selection response. However, the gen etic variance was exhausted after two cycles of selection and genetic correlations among the component traits of the index became increasing ly positive. Complex segregation analysis (CSA) of index scores in the Davis population supports a mixed Mendelian model with a completely d ominant segregating major gene accounting for 20 per cent of the pheno typic variance. This model estimates h(2) = 0.9 for I and is discussed as it pertains to the effects of selection on the genetic parameters of the selected population.