Analysis of cellulose microfibril angle using a linear mixed model in Pinus taeda clones

Abstract

Variation in microfibril angle (MFA) (degrees) among loblolly pine ( Pinus taeda L.) full-sib families and clones was investigated using 43 clones from nine full-sib crosses tested at two locations. When the experiments were 12 years old, a total of 316 trees were drilled and 12 mm thick wood increment cores were collected. MFA for each growth ring in the wood core was measured using the SilviScan-2 tool. A quadratic mixed model was fitted to evaluate the MFA variation over different rings. Among the error covariance structures tested in the model, autoregressive order 1 was the best model for producing MFA estimates with the smallest errors. Estimated MFA was about 33° in the pith (ring 1) of the trees and decreased to 18° in the outer wood (ring 11). Full-sib crosses and clones within crosses explained about 12.5% of the total phenotypic variation. Repeatability of full-sib family means (H2f = 0.46) was moderate but repeatability of clone means was high (H2c = 0.79). Although it is possible to improve (decrease) MFA with recurrent selection in tree improvement programs to improve lumber quality, cost efficient and rapid methods for measuring MFA are needed.