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Trends in variances and heritabilities with age for growth traits in eucalyptus spacing experiments

Bouvet J.M., Vigneron P., Gouma R., Saya A.R.. 2003. Silvae Genetica, 52 (3-4) : p. 121-133.

Three experimental designs were carried out in the Congo to analyse the impact of spacing on trends in variance and heritability with age and to assess the genotype by spacing interaction in a eucalyptus breeding programme. Three populations of eucalyptus hybrids encompassing respectively 12 clones, 12 and 16 full sib families were established in square or rectangular plots of 30, 36 and 36 trees respectively, at spacings of 625, 1111 and 2500 trees/ha. Height and circumference were measured at different ages, from the juvenile stage up to the adult size of the trees. Results showed that genetic effect was significant from the juvenile stage for the three experiments. Family by spacing interaction was not significant throughout the growth period but, for the clonal population, the interaction was highly significant after age 3, with changes in clone ranking. Trends in between or within family or clone coefficient of variation with age exhibited two main phases. During the first phase the coefficient of variation decreased and during the second phases it was constant for the genetic effect and strongly increases in the case of within clone and within family effect. This two phases could correspond to a juvenile and a mature phase. In the case of these three experiments some results showed that the juvenile phase could be reduced with closer spacing, as suggested by the Franklin's model. Heritabilities based on the clone and family mean were very high for the three experiments due to the sample size and the high control of the environment in the design. Heritabilities based on individual trees were smaller because of the high within plot variance. These two parameters rapidly reached a plateau and the two phases mentioned for variances were not observed. Although heritability at close spacing decreased with age for the family experiments, due to the strong increase of the within clone and family variance, the impact of spacing was not statistically significant. The high heritability on the family means basis and the absence of family by spacing inter action permits the family selection at close spacing with a good efficiency specially during the juvenile phase.

Mots-clés : eucalyptus; héritabilité; variation génétique; croissance; congo

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