Narrow-sense heritability of heartwood variation in a teak ( <i>Tectona grandis</i> ) clonal trial and its potential for tree improvement

Teak (Tectona grandis L. f.) is a valuable tropical tree species renowned for its high-quality heartwood and excellent adaptability. Understanding the heritability of key traits such as growth characteristics and heartwood formation is essential for designing effective breeding programs aimed at improving wood quality and productivity. In the present study, we assessed the heritability of various traits based on genetic relationship matrices, including stem diameter, stem height, heartwood width, and sapwood depth, using 538 stems from a clonal trial in Thailand. Single-nucleotide polymorphisms derived from MIG-seq were used to construct additive (GA) and dominant (GD) genetic relationship matrices. The results indicated that heritability estimates based on GA were generally higher than those based on GD, suggesting the predominant role of additive genetic variance in most traits. Notably, sapwood depth exhibited equivalent heritability in both matrices, highlighting the potential significance of non-additive genetic effects. Both stem diameter and height heritabilities decreased with age, likely reflecting a shift in genetic control during maturation. Heartwood width exhibited moderate heritability (16–22%), which was influenced by the low heritability of stem diameter. In contrast, higher heritability in both additive and dominance effects for sapwood depth was detected, which evokes the importance of allelic combination. These findings emphasize the importance of accounting for trait-specific genetic architecture in teak breeding strategies, particularly for traits such as sapwood depth, where non-additive effects may play a significant role. This study provides critical insights into the genetic basis of growth and wood formation in teak, paving the way for optimized genetic improvement programs.