Control by Indole-3-Acetic Acid of Wood Production in Pinus radiata D. Don Segments in Culture

Abstract

The effect of indole-3-acetic acid (IAA) on stem radius growth, tracheid lumen diameter, and tracheid wall thickness in P. radiata was investigated. Stem segments from trees that normally produce high-density wood and from trees that normally produce low-density wood were grown in vitro at a number of IAA concentrations between 0 and 20 mg l^-1. Maximum increase in stem radius and maximum tracheid lumen diameter were found at IAA concentrations of 6-10 mg l^-1. Tracheid wall thickness increased approximately linearly as IAA concentration was increased up to 20 mg l^-1. Absolute differences in radial stem increase and in cell lumen diameter between the high- and the low-density stems were greatest at IAA concentrations of 4-10 mg l^-1. At low or high IAA concentrations, absolute differences between the clones in their stem radial increase and in their tracheid lumen diameter were small. Proportional differences between the clones in these two factors were greatest at IAA concentrations of 10 mg l^-1. Clonal differences in the tracheid wall volume per unit stem volume could account for the differences in wood density only at IAA concentrations of 4-10 mg l^-1.