Using B-splines for growth curve classification: applications to selection of eucalypt clones

The cumulative growth of a tree is the result of genotypic and environmental effects and their interaction. In tree breeding and selection, assessment of genetic effects over time is an important task. To address this, we focused on volume growth of 77 clones of eucalypt hybrids Eucalyptus urophylla×Eucalyptus grandis measured in a clonal test. A new methodology of growth modeling using B-splines is introduced and applied to this population. Classification of the curves is made using a hierarchical robust clustering on B-spline function coefficients. Clusters obtained from this method can be interpreted as representing different strategies of growth. It allows selection of clones in an easy and graphical way. The accuracy of the B-splines method, clone selection strategy, and the perspective for the breeding program are discussed in the frame of the eucalypt genetic improvement program of the Congo.