Variation in the Incidence of Resin-filled Shakes and Wood Density among Open-pollinated Families ofPinus elliottiiPlanted at Four Different Sites

Abstract

SYNOPSISA study on the incidence and severity of resin-filled shakes was carried out on 36 open-pollinated families established at four different sites. The objectives were to study the distribution of shakes within and between trees, and how it is affected by genetics and environment.In general a clear pattern in the variation among families was observed suggesting that there is some genetic influence. However, between the four different sites the among-family patterns of variation in resin shake propensity, differences between trees within families, and the distribution within tree stems, were extremely variable and inconsistent. From this it is evident that some genotypes seem to respond differently to the influences of environment. Resin shakes often occurred in the basal part of the tree stem, often extending into the stump, but the frequency of occurrence varied considerably between sites. Shakes occurring higher up in the stem were often associated with large knots, knot clusters and forks.The trees sampled at about sea level exhibited a much lower incidence of resin shakes and produced wood of much higher density than the trees sampled at higher altitudes, but no direct relationship of any significance between the incidence of resin shakes and these factors could be found. No relationship could also be found between differences in shake intensity among individual trees and differences in wood density.A study aimed at understanding the relationship between resin shake formation, fracture energy and the shear strength of the wood, and the factors controlling shear strength, is proposed. Such information would be an important requirement for developing an effective breeding strategy aimed at manipulating those wood properties affecting the shear strength of the stem.