Genotype by environment interaction and teak (Tectona grandis L.) selection in Costa Rica

Abstract A teak progeny trial was established with four replicates at different sites along the northern Pacific region of Costa Rica. The trials followed a randomized block design, with 28 open pollinated families and 36 seedlings per family per site. Data from 7 years-old trees was analyzed both for each test location separately and for all locations combined. High individual heritability was found for diameter, which translates to higher breeding potential. The all locations combined analysis showed high genetic variation, with individual heritabilities reaching up to 22 %. Genotype by Environment (GxE) interactions explained only 2.5 % of total phenotypic variation. The genetic correlation (rg) among all four sites was 0.69. Hence, it is concluded that GxE interactions are not problematic for breeding purposes since they are not complex in nature. This teak breeding population showed strong genetic stability and performed well in most environments in the study area. The Hojancha location showed high genetic correlation with all other sites; therefore, it should be chosen for future testing and selection of elite genotypes. Selection of the 20 best individuals, allowing for up to two individuals per family, would result in a 1.78 cm (11 %) gain in diameter. Furthermore, based on this selection the inbreeding coefficient (F) in the offspring would only reach 2.9 %, while the expected effective population size (Ne) would be16.97 individuals. This selection scheme could reduce rotation age by almost two years, since the diameter goal of 40 cm would be reached earlier than the usual 20 years cycle. The results suggest that the progeny trial can be maintained as a single breeding population, suitable for planting in any site along the Northern Pacific region of Costa Rica.