Growth response of eucalyptus clones to different soils in a nursery environment

Abstract

A nursery clonal test of 20 clones was established at the University of Stellenbosch on eight soil treatments consisting of combination of four soil types and two lime levels. One clone was from first-generation and 15 were from second-generation Eucalyptus grandis selected in 13 different open pollinated family trials and two full-sib trials. Three hybrid clones were selected from two E. grandis x E. camaldulensis and one. Grandis x E. urophylla families. Soil collection was done in four different places in the Western Cape, specifically Lorensford near Somerset West, Pampoenvlei near Malmesbury and Grabouw and Helshoogte near Stellenbosch. The yellowish soil from Grabouw and the reddish soil from Helshoogte were clayey while the black and light soils from Lourensford and Pampoenvlei respectively were sandy soils. Two lime levels, with or without lime application, on these soils generated eight soil treatments. Results are firstly presented in tables and the delineation of significant differences between the rankings of clones, replications, soil types, soil treatments for selected given by Duncan’s New Multiple Range Test is included. Graphical presentations are used to illustrate some of the trends over all the single effects, that is soil types, lime levels and clones. Analysis of variance for the simplified model detected a highly significant difference for soil treatments, which is the combination of different soil types and lime levels. Quite strong correlations between the soil treatments were also evident. Assessments of height, diameter, root and shoot mass were made at age 12, 18 and 24 weeks. Number of branches was assessed at 24 weeks. All the single effects were found to be statistically different for most variables at all ages. The most outstanding on the two-way interactions is the general insignificance of clone x soil type, clone x lime and soil type x lime interaction, for height and diameter growth bur indeed not for mass root mass. This might mean that height and diameter alone are not sensitive enough but when leaves are included in mass (like a volume) then more expression is obtained justifying the interaction found at 24 weeks for root and shoot mass for all two-way interactions. Generally the three-way interaction seems insignificant. Once again, shoot mass shows some sensitivity being perhaps an indication of “whole tree” response to environment. Analysis of variance for the simplified model showed that soil treatment (soil type x lime), results were highly significant for all the variables studied. When diameter and height means were studied in terms of phenotypic correlations between sites (soil treatments), quite strong correlations were evident between the soil treatments. Clone x soil treatment interaction, was also detected by means of regression coefficients. Some clones were found to be stable for variable shoot mass, for instance, AG1, AG3-B, AG6, AG12 and AG14. Average stability clones wereGU1, GC1 and GC2 while unstable clones were identified as AG5, AG8, AG11 and AG15. The magnitude of genotype x environment interaction is low implying that it will not affect broad sense heritability (there are too few clones to reliably estimate) as well as genetic gain. It is noted that genotype x environment interaction tends to disappear for height and diameter over time, while it remains for shoot mass (volume of the tree) and number of branches at age 24 weeks. The results from this study are encouraging for further research aimed at developing techniques for early prediction of genotype x environment interaction in eucalypt trees.