Determining the Optimal Harvesting Period of Melia dubia by Expression of Cellulose and Lignin Biosynthesis Genes for Improved Pulpwood Quality

Abstract This study investigated the influence of tree diameter at breast height ( DBH ) on Melia dubia pulpwood properties via gene expression analysis. In this study, different DBH classes, such as 10.0 cm, 15.0 cm and 20.0 cm, were considered for pulpwood chemical properties. Compared with the other classes, the 15.0 cm DBH class presented the highest cellulose content (69.6%), moderate lignin content (21.0%) and kappa number value (17.2). Additionally, it has the highest tear index (4.9), indicating stronger paper quality. On the other hand, the 20.0 cm DBH class had greater lignin content (24.8%) and a kappa number of 18.6, reducing its pulping efficiency. Furthermore, gene expression analysis revealed that higher expression of cellulose synthesis genes (Ces2, Ces4) was associated with the 15.0 cm DBH class, whereas lignin biosynthesis genes (CAD2, LAC8) were highly expressed in the 20.0 cm DBH class. Additionally, the correlations between gene expression and wood properties and growth traits corresponded, suggesting that DBH influences cellulose and lignin biosynthesis, affecting pulp quality. Thus, the 15.0 cm DBH class is optimal for harvesting, balancing high cellulose content and favourable lignin levels, leading to improved pulp yield and paper strength.