Genetic parameters for early growth and biomass traits of Pinus radiata D. Don under different water regimes

In Chile, genetic improvement of Radiata pine has been directed towards characters such as volume, form and wood density. Estimation of genetic parameters for growth and biomass traits in young seedlings, as a tool for early indirect selection in the P. radiata breeding program, has not been explored yet. We aimed to estimate genetic parameters for growth and biomass traits. Five-month-old P. radiata seedlings grown under wellwatered (WW) and water stress (WS) regimes were evaluated. Root collar diameter, height, shoot dry weight, root dry weight, total dry weight, height/diameter ratio and root/shoot ratio were analyzed in both treatments. Trait with the highest heritability was root/shoot ratio in WW and WS regime (h² = 0.80 and 0.63 respectively). The highest genetic correlation was between height and shoot dry weight (r_g = 0.90), under WW regime. In contrast, there were negative genetic correlations between root collar diameter and height/diameter ratio under WS regime. To breed for drought tolerance, traits such as height and root collar diameter would be effective targets for indirect selection since estimated heritabilities are high, there is sizable genetic variation, they are easily assessed, they can be measured non-destructively and they have a high genetic correlation with root/shoot ratio, a trait related to drought tolerance. The measurement of dry weights for early selection purposes is not recommended.