Original Articles

A repeatability study of trait assessment in a Pinus patula breeding programme

Published in: The Southern African Forestry Journal
Volume 185, issue 1, 1999, pages: 38–44
DOI: 10.1080/10295925.1999.9631225
Author(s): MarianneH. Hettasch, Republic of South Africa, StephenD. Verryn, Republic of South Africa

Abstract

A repeatability study of tree height, diameter at breast height (DBH), stem and crown form assessments was undertaken. Trees were measured four times by two independent teams. The repeatability of the five traits was estimated. The effect of repeatability on the heritability of the traits was determined. In order to obtain an indication of the feasibility of repeating measurements, the genetic gains were calculated for a hypothetical breeding population. The Best Linear Prediction (BLP) rankings of the four repetitions of the measurements were compared, with selection being based on volume, stem and crown. The repeatabilities for height (0,81), DBH (0,98) and volume (0,97) were high and the heritabilities of these traits showed only small increases with repeated measurements. Stem and crown form which were scored on a subjective scale, showed a repeatability of 0,61 and 0,62 respectively. Repeating scoring of these traits lead to bigger increases in the heritability with repeated measurements. Increases in genetic gains with repeated measurement of stem and crown varied from 0,3% for DBH to 1% for stem form. Only a total of 30% of the top 10 BLUP rankings of the four repetitions of the measurements corresponded.

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