Analysis of Genotype-Environment Interactions in Gmelina arborea Provenance Trials for Plantation Forestry in South-Eastern Nigeria

Matching superior Gmelina arborea genetic material to specific plantation environments is a fundamental requirement for optimising productivity in the commercial timber plantations of south-eastern Nigeria, yet formal provenance testing under local ecotypic conditions is limited in the published literature for this region. This study analyses genotype-environment interactions in a multi-site provenance trial of Gmelina arborea established at three contrasting sites in Imo, Cross River, and Akwa Ibom States, representing a gradient of rainfall, soil type, and altitude. Twenty provenances sourced from national and international germplasm collections were tested in a randomised complete block design with six replications per site. Height, diameter at breast height, survival, stem straightness, and disease incidence were assessed at two, four, and six years. AMMI (additive main effects and multiplicative interaction) analysis was used to quantify genotype-environment interaction effects and identify broadly adapted versus specifically adapted provenances. Results revealed significant genotype-environment interactions for all growth traits, indicating that site-specific provenance selection substantially outperforms generic planting material. Four provenances from Queensland, Australia and two Nigerian local provenances showed superior broad adaptation across all three sites. Site-specific top performers offered up to 34% volume gain over the worst-performing local standard. Disease tolerance was strongly provenance-dependent at the humid southern sites. The study provides actionable provenance selection recommendations for each site type and argues for establishment of a national Gmelina provenance testing network under the Forestry Research Institute of Nigeria. Keywords: Gmelina arborea, provenance trial, genotype-environment interaction, plantation forestry, south-eastern Nigeria