Genotype by environment interaction for volume growth at 6 years of age in a series of five<i>Pinus patula</i>progeny trials in southern Africa

Synopsis Genotype x environment interaction was investigated in a series of 5 Pinus patula progeny trials planted by the Institute for Commercial Forestry Research in southern Africa. The trials were established from Mpumalanga to the North-eastern Cape in a balanced 7x7 lattice design with 48 common treatments that comprised 45 unrelated, open-pollinated families and 3 genetic checks. The environments sampled represented a range of climatic and site quality gradients. All trees were assessed for height and diameter at 6 years of age. Survival was 87% and ranged from 83 to 92% across the 5 sites. Growth on the 5 sites varied from 0,034m3 to 0,065m3 / tree and single site heritability estimates ranged from 0,17 to 0,43. The interactions between site and treatment were highly significant. The overall GxE variance represented approximately 21%of the variance due to treatment. EstimatedType B genetic correlations averaged 0,76 for all pairs of sites with a range ofO,4 to 1,0 and were correlated with median rainfall during the spring period from September to November. Thejoint regression method was utilised to determine the stability of genotypes across sites. Some rank changes were detected across the 5 locations but these were limited to 15%ofthe families tested. Results indicate that GxE may be important for Pinus patula within southern Africa and that some form of regionalisation may be possible using some simple environmental variables such as rainfall.