Original article Estimation of genetic parameters in eastern cottonwood (Populus deltoïdes Bartr.). Consequence for the breeding strategy

Summary — Poplars bred for the future by INRA include two North American species: eastern and black cottonwood and the European black poplar. The breeding strategy, now under discussion, needs to be based on the biological and genetic properties of the species. The present study aims to estimate the genetic parameters in the eastern cottonwood (Populus deltoiaes Bartr.). A factorial crossing design involving 6 females and 6 males was carried out between 1971 and 1980. Observations on copies of the parents and of their offsprings were made in 1985 and 1986 in a design laid out in the INRA, experimental nursery near Orldans, France. Observations concerned phenology, growth and wood quality. Firstly, the results showed a significant variability of most traits, whether among parents, among families or among cloned full-sibs; but this variability was greater among parents than among families which can be explained by the assumption that allelic fixation occurred in the natural stands the parents originated from. This allelic fixation was high for phenologic traits, moderate for growth traits and absent for wood quality traits. Secondly, heritabilities were estimated. Broad sense heritabilities were generally high and significant for all types of traits. Narrow sense heritabilities estimated from parent-offspring regression are extremely low for wood quality traits. Thirdly, additive genetic correlations between traits were estimated. Significant values were found between phenology and growth traits and between growth termination and wood basic density, which means that fast growing genotypes should be looked for among early starters rather than among late growers. The latter will tend to produce wood with a low basic density which is not suitable for poplar