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Yiran Yu, James Harding, and Thomas Famula

Additive genetic components of variance and narrow-sense heritabilities were estimated for flowering time and cut-flower yield for generations 8-13 of the Davis population of gerbera, using the least squares (LS) and restricted maximum likelihood (REML)

methods. Estimates of heritability for flowering time were 0.54 and 0.50 using REML and LS, respectively, indicating a close agreement between the two methods. However, estimates of heritability for cut-flower yield were 0.30 and 0.46 from REML and LS. This may result from the fact that cut-flower yield was selected in each generation; flowering time was not. Realized heritability for cut-flower yield was estimated to be 0.26 which agreeded more closely with the heritability estimated from REML. The advantages of REML, and its applications in the estimation of components of genetic variance and heritability of plant populations are discussed.

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Hongzhan Huang, James Harding, and Thomas Byrne

Inbreeding depression is found in most flower crops. Limited population size can cause inbreeding even in outcrossed populations. The Davis population of Gerbera hybrida has been selected for increasing flower yield for 15 generations. The mean yield per plant of the population has been increased from 14.2 to 28.0 flowers per winter six-month period. In each generation 23 to 80 selected parents have been crossed at random. Inbreeding coefficients were estimated from the pedigrees of each of the 6199 plants in the 16 generations. The inbreeding level in this population was found to increase in each generation and currently is 16.5%. Mean yield and inbreeding per family have a statistically significant negative correlation in generations 13 to 16. The results indicate that inbreeding is increasing in this randomly outcrossed population because of its finite number of parents, and that yield is reduced by 3.9 flowers per six-month due to inbreeding.

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Hongzhan Huang, James Harding, and Thomas Bvrne

The effects of long-term genetic improvement are measured by selection response predicted from estimates of narrow-sense heritability. However, changes of population mean must be partitioned into genetic and environmental components-in order to accurately estimate selection response.

A long-term selection experiment for cut-flower yield in the Davis population of gerbera (Gerbera hybrida, Compositae) was conducted for sixteen generations. Breeding value was estimated for individual plants in the population using Best Linear Unbiased Prediction (BLUP). Genetic change was calculated from breeding values of individual plants in each generation. The results of this study indicate: the long-term selection experiment was successful and necessary for genetic improvement. Genetic change over sixteen generations was 33 flowers. Mean breeding values increased monotonously with an “S” shape pattern. Environmental effects fluctuated from generation to generation. Cut-flower yield in the Davis population of gerbera will continuously respond to selection.

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Yiran Yu, James Harding, and Thomas Byrne

Genetic components of variance and heritability of flowering time were estimated for five generations of the Davis Populationof Gerbera hybrids, Composite, Estimates of narrow-sense heritability averaged 0.50 and broad-sense heritability averaged 0.77 using the NCII design. Narrow-sense heritability was also estimated with two models of parent-offspring regression, resulting in average heritability of 0.49 and 0.51. Estimates of components of variance indicated that the major genetic effect controlling flowering time is additive. However, the dominance component accounted for 28% of the total variance; the environmental component was only 23%. Flowering time is negatively correlated with cut-flower yield. The phenotypic coefficient was –0.34; genetic correlations were –0.47 when estimated from the NCII design, and –0.72 when estimated from the parent-off-spring method. A practical model was constructed to assess the efficiency of indirect selection for cut-flower yield using flowering time as a marker trait. The advantages of indirect selection accruing from increased population size and reduced generation time are discussed.

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Yiran Yu, James Harding, and Thomas Byrne

Genetic components of variance and heritability of flowering time were estimated for five generations of the Davis Populationof Gerbera hybrids, Composite, Estimates of narrow-sense heritability averaged 0.50 and broad-sense heritability averaged 0.77 using the NCII design. Narrow-sense heritability was also estimated with two models of parent-offspring regression, resulting in average heritability of 0.49 and 0.51. Estimates of components of variance indicated that the major genetic effect controlling flowering time is additive. However, the dominance component accounted for 28% of the total variance; the environmental component was only 23%. Flowering time is negatively correlated with cut-flower yield. The phenotypic coefficient was –0.34; genetic correlations were –0.47 when estimated from the NCII design, and –0.72 when estimated from the parent-off-spring method. A practical model was constructed to assess the efficiency of indirect selection for cut-flower yield using flowering time as a marker trait. The advantages of indirect selection accruing from increased population size and reduced generation time are discussed.

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Kenneth R. Tourjee, James Harding, and Thomas G. Byrne

Ligule color of a Gerbera jamesonii H. Bolus ex Hooker population was analyzed with a reflectance spectrophotometer having a spectral capability of 400 to 700 nm and a cv <3% for the variables hue, chroma, and value. The observations for each variable had a continuous distribution; these broad distributions are possibly bimodal. The repeatability of hue, chroma, and value, determined as the correlation between measurements made on plants in December and those made on the same plants the following April, are 0.83, 0.82, and 0.86, respectively. The phenotypic correlations between value and chroma, value and hue, and chroma and hue are -0.35, 0.73, and 0.11, respectively. Some possible biochemical implications concerning the interaction of anthocyanin and carotenoid pigments are discussed. Reflectance spectroscopy and Commission International de l'Eclairage 1976 (L* a* b*) color space notation provide an objective and precise method for incorporating color into a recurrent selection program.

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Kenneth R. Tourjee, James Harding, and Thomas G. Byrne

The frequency distribution of gerbera flower hue in the Davis population of gerbera appears continuous and bimodal. This suggests that a gene of large effect may be segregating in a background of polygenic variation. CSA is a statistical technique developed in genetic epidemiology for investigating such complex traits without the need of inbred lines. The REGC program of SAGE (Elston, LSU Medical Center, New Orleans) uses the regressive models of G. Bonney (1984) through pedigree analysis to provide estimates of major gene parameters and residual correlations among relatives. Pedigrees obtained from generations 14, 15, and 16 indicate that a major dominant gene for hue is segregating and accounting for -0.66 of the total variation. The genotypic means are 32 degrees and 71 degrees for the aa and bb genotypes, respectively. The a allele is dominant to the b allele and has a frequency of 0.55. The residual parent-offspring correlation estimate is 0.2 and measures the genetic contribution to the remainder of the variance.

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Kenneth R. Tourjee, James Harding, and Thomas G. Byrne

The frequency distribution of gerbera flower hue in the Davis Population of Gerbera appears continuous and bimodal. This suggests that a gene of large effect may be segregating in a background of polygenic variation. CSA is a statistical technique developed in genetic epidemiology for investigating such complex traits, without the need of inbred lines. The REGC program of SAGE (Elston, LSU Med. Center, New Orleans) utilizes the regressive models of G. Bonney (1984) through pedigree analysis to provide estimates of major gene parameters and residual correlations among relatives. Pedigrees obtained from generations 14, 15, and 16 indicate that a major dominant gene for hue is segregating and accounting for ∼ 0.66 of the total variation. The genotypic means are 32 degrees and 71 degrees for the aa and bb genotypes, respectively. The `a' allele is dominant to the `b' allele and has a frequency of 0.55. The residual parent-offspring correlation estimate is 0.2, and measures the genetic contribution to the remainder of the variance.

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Kenneth R. Tourjee, James Harding, and Thomas G. Byrne

The development of gerbera (Gerbera jamesonii H. Bolus ex. Hooker) as a floricultural crop is traced from its collection as a botanical novelty in South Africa to its establishment as a commercial crop in the 1930s. The origin of the cultivated germplasm, G. jamesonii and G. viridifolia (DC) Schultz- Bipontinus, is discussed, as well as breeding work that occurred in Europe and the United States. The contributions of the two species to the cultivated germplasm is unknown. Early breeding in Europe was conducted by RI. Lynch at the Cambridge Botanic Gardens in England, R. Adnet at La Rosarie in Antibes, France; and by C. Sprenger in Italy. In the United States, early work was done at estates in New Jersey by Herrington and Atkins, and by the commercial growers Jaenicke and the J.L. Childs' Seed Co. Establishing the cold hardiness of the crop for temperate climates was an early goal of horticulturists and breeders. Much of the cultivated germplasm can be traced to material that passed through Cambridge and Antibes.

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Lin Wu, Janquo Chen, Hong Lin, Phillip Van Mantgem, M. Ali Harivandi, and James A. Harding

The effects of regenerant wastewater irrigation and high concentrations of Ca2+, K+, Mg2+, and Cl on growth and ion uptake of nine species of landscape plants were studied. Significant differences in chloride tolerance were detected among the species. Generally, the species that had greater uptake of chloride grew less than species that took up less amounts of chloride. Lace fern (Athyrium filix-femina Roth.) had the highest tissue Cl concentration and was the most affected. Hydrangea (Hydrangea macrophylla Ser.) also had high tissue Cl concentration, but showed no growth reduction. Its tolerance was attributable to a high tissue Ca concentration. The data suggest that in the species tested, higher tissue Ca concentrations were positively correlated with plant tolerance to Cl. Overall, the Cl concentration in the wastewater seems to be the factor most likely to create problems for the landscape plants. However, severe negative effects will probably be noticed only for very sensitive plant species, but it is important to determine this before applying regenerant irrigation water.