T. Byrne

Estimation of heritability and response to selection for cut-flower yield in gerbera

SummaryHeritabilities and responses to selection for cut flower yield were estimated for a population of gerbera. Broad-sense heritabilities averaged 42 percent, but may be as high as 66 percent. Narrow sense heritabilities averaged 68 percent when based on half-sib families, and averaged 60 percent when based on parent-offspring regression. These results suggest that most genetic variance for flower yield is additive.However, estimates of realized heritability averaged only 16 percent and inbreeding depression was estimated to be at least 38 percent, suggesting a major role for non-additive genetic variance. Nonetheless, selection for cut flower yield is expected to be successful.

Heritability of cut-flower vase longevity in Gerbera

SummaryEstimates of broad-sense heritability for cut-flower vase longevity were 36 and 46 percent for a sample of Gerbera clones. Estimates of narrow-sense heritability for vase longevity were 0, 24 and 38 percent over 3 generations of the Davis Population. Response to selection for this character in this population is expected to be slow.

Quantitative analysis of correlations among flower traits in Gerbera hybrida Compositae : 1. Genetic and environmental correlations.

SummaryPhenotypic (rp), genetic (rg), and environmental, (re) correlations were estimated for 38 flower traits in the Davis population of gerbera (Gerbera hybrida, Compositae). Fifty-two percent of rp and 38% of rg were statistically significant at P < 0.05. Significant negative rp were infrequent, but significant negative rg occurred in 10% of cases. There was a negative correlation between estimates of rg and re, resulting in cases where rg was significant, but rp was not. Individual traits varied in their tendency to correlate phenotypically or genetically, and positively or negatively, with other traits. Traits within the same morphological category, such as disk florets or transitional florets, were more highly intercorrelated than were traits from different categories.

Quantitative analysis of correlations among flower traits in Gerbera hybrida, Compositae. 2. Direct and mean correlated response to selection.

SummaryA Mean Correlation Response (MCR) model was developed to estimate the relative effectiveness of direct selection when other traits also respond to the selection. A measure of the relative effects of mean correlated response and direct response (R) and a measure of the relative efficiency of direct selection (IE) were applied to a genetic correlation matrix of 38 traits. These were measurements of inflorescence, receptacle and involucre, scape, disk florets, ray florets, and trans florets in the Davis population of Gerbera hybrida, Compositae. Generally, traits with high heritability had high direct and mean correlated response; these were often traits measuring disk and trans florets. Traits with low heritability had low direct and mean correlated response; these were often traits measuring the inflorescence. Traits of the inflorescence had the lowest efficiency of direct to mean correlated response.

Heritability of inflorescence and floret traits in gerbera

SummaryHeritability, repeatability, and components of variance were estimated for 68 morphological characters describing the inflorescence, scape, and florets of Gerbera hybrida. The heritability estimates were generally moderate to high for simple dimension characters and characters which were the mean of several measurements, low to moderate for ratio and composite characters, and low for enumeration characters and characters describing the intraplant variation of traits. The repeatability estimates were generally low for intraplant variation characters, moderate for simple ratio characters, and largest for composite and mean characters. For most of the characters, the variance among inflorescences from the same plant was the largest portion of the total phenotypic variance.

Components of genetic variation for cut-flower yield in the Davis Population of Gerbera

SummaryGenetic variances for cut-flower yield in Gerbera hybrida were partitioned into additive and dominance components. Mean additive variance was 37.3 with a standard error of 12.9. Mean dominance variance was 12.7 with a standard error of 32.6. The dominance ratio was 0.34. Narrow sense heritability, estimated from these components of variance, averaged 0.42 with a standard error of 0.13. Heritabilities estimated from parent-offspring regression averaged 0.25. Gain from selection was less then expected; realized heritabilities were approximately 0.20.

Complex segregation analysis of Gerbera flower colour

The distribution of hue (CIELAB colour notation) classes among flowers of the Davis population of gerbera (Gerbera jamesonii H. Bolus ex Hooker) appears bimodal. This suggests that the genetic control of hue is determined by the segregation of a gene with large effect modified by additional genes with smaller effects. Complex segregation analysis (CSA), routinely employed in human genetic epidemiology, was used to study both qualitative and quantitative variation. CSA applies pedigree analysis through the consideration of transmission probabilities to optimize likelihood functions of various genetic models. Applying this technique to study flower hue of a sample representing generations 14, 15 and 16 of the Davis population, allowed identification of a putative dominant major gene with genotypic values for the dominant homozygote, heterozygote and recessive homozygote of 32, 32 and 71 degrees, respectively. This corresponds to the modes of the hue frequency distribution for the population. The putative major gene represents 0.66 of the total variation. The residual parent-offspring correlation (ρpo = 0.2) measures the genetic contribution to the remainder of the variance.

Heritability of consumer preference in Gerbera

SummaryHeritabilities and response to selection for consumer preference were estimated for a population of Gerbera. Broad-sense heritability was estimated to be 62 percent. Narrow-sense heritability was estimated by parentoffspring regression to be 76 percent, by full-sib family analysis to be 54 percent, and by half-sib family analysis to be 72 percent. These estimates indicate that most of the variance for consumer preference is genetic and that most of the genetic variance is additive. Estimates of realized heritability averaged 71 percent indicating substantial response of this population to selection for consumer preference.

Estimation of components of genetic variance and heritability for flowering time and yield in gerbera using Derivative-Free Restricted Maximum Likelihood (DFRML)

SummaryAdditive genetic components of variance and narrow-sense heritabilities were estimated for flowering time (FT) and cut-flower yield (Y) for six generations of the Davis Population of gerbera using Derivative-Free Restricted Maximum Likelihood (DFRML). Additive genetic variance accounted for 54% of the total variability for FT and 30% of the total variability for Y. The heritability of FT (0.54) agreed with previous ANOVA-based estimates. However, the heritability of Y (0.30) was substantially lower than estimates using ANOVA. The advantages of DFRML and its applications in the estimation of components of genetic variance and heritabilities of plant populations are discussed.

Estimation of long-term genetic improvement for gerbera using the best linear unbiased prediction (BLUP) procedure

Long-term genetic improvement is measured by the selection response predicted from estimates of narrow-sense heritability. Accurate estimates of selection response require partitioning the change of population mean into genetic and environmental components. A selection experiment for cut-flower yield was conducted for 16 generations in the Davis population of gerbera (Gerbera hybrida, Compositae). Breeding values were estimated for individual plants in the population using the best linear unbiased prediction (BLUP) procedure. Genetic change in each generation was calculated from the breeding values of individual plants. The results of this study indicate that long-term selection was successful and necessary for the genetic improvement in cut-flower yield. Genetic improvement in mean breeding value over 16 generations was 33 flowers. Mean breeding values increased monotonically with an S-shape pattern while environmental effects fluctuated from generation to generation. Results predict that cut-flower yield in the Davis population of gerbera will continue to respond to selection.