The effectiveness of cloning for the genetic improvement of Mexican white cypress Cupressus lusitanica (Mill.)
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ORIGINAL PAPER
The effectiveness of cloning for the genetic improvement of Mexican white cypress Cupressus lusitanica (Mill.) Heidi S. Dungey & John H. Russell & João Costa e Silva & Charlie B. Low & Mark A. Miller & Kane R. Fleet & Graham T. Stovold
Received: 26 April 2012 / Revised: 11 August 2012 / Accepted: 18 August 2012 / Published online: 25 October 2012 # Springer-Verlag Berlin Heidelberg 2012
Abstract Two trials on Mexican cypress Cupressus lusitanica Miller in the North Island of New Zealand were assessed for diameter at breast height and at one site, subjective scores for branch size and stem canker (caused by Seiridium spp.) at age 6 from planting. The trials comprised 15 open-pollinated families, represented by both cloned and seedling progeny. Linear mixed model methodology, using a spatial model for the residuals, was applied to estimate genetic parameters. Estimated narrow-sense heritabilities were moderate to high for diameter at breast height (range from 0.46 to 0.62), stem canker (≈0.30) and branch size (range from 0.23 to 0.45) and did not appear to differ significantly between propagule types for all traits. Clonally replicated progeny led to an increase in accuracy of selection for additive genetic merit when compared with seedling testing, with the improvement being greater for traits with lower narrow-sense heritabilities. Estimated additive genetic Communicated by R. Burdon H. S. Dungey (*) : C. B. Low : M. A. Miller : K. R. Fleet : G. T. Stovold Scion, Te Papa Tipu Innovation Park, 49 Sala Street, Private Bag 3020, Rotorua 3046, New Zealand e-mail: [email protected] J. H. Russell Ministry of Forests, Lands and Natural Resources Operations, Cowichan Lake Research Station, Box 335, 7060 Forestry Rd, Mesachie Lake, BC V0R2N0, Canada J. Costa e Silva Centro de Estudos Florestais, Departamento dos Recursos Naturais, Ambiente e Território, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada de Ajuda, 1349-017, Lisbon, Portugal
correlations between cloned and seedling progeny were moderate to high (≥0.65) for diameter and branch size, indicating that selection decisions would not be substantially changed using either propagule type for progeny testing. All estimates of non-additive genetic variation based on the cloned progeny were non-significant. The use of spatial analysis was effective for diameter and branch size, but not for stem canker. No significant genotype by environment interaction was detected for diameter. Implications of the results for breeding and deployment of C. lusitanica are discussed. Keywords Cupressus lusitanica . Clones . Genetic parameters . Propagule type . Stem canker . Seiridium
Introduction Capturing genetic gain in tree improvement programmes classically involves recurrent selection for additive gene effects and deployment of this gain through open-pollinated (OP) seed orchards. The advantages of deploying elite clones in reforestation over traditional seed orchards include, but are not limited to, increasing genetic gain per unit
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