Geographic patterns of genetic variation in Eucalyptus globulus ssp. globulus and a revised racial classification

Abstract

The geographic patterns of genetic variation in a wide variety of quantitative traits were studied in Eucalyptus globulus ssp. globulus and its intergrades, leading to a revised racial classification. The analysis was based on 35 traits assessed in five field trials in northern Tasmania from approximately 500 open-pollinated families, encompassing 49 collection localities in native stands. There were significant differences between the collection localities for most traits. While growth and survival traits exhibited weak spatial structuring, there were clear regional patterns in bark thickness, wood basic density, flowering precocity and some aspects of juvenile leaf morphology. There were a number of significant correlations between trait locality means, but few simple correlations between the regional patterns observed and climate. Multivariate analyses indicated that the localities could be effectively amalgamated into larger, geographically concordant races. A hierarchy of five major groupings of 13 races and 20 subraces is proposed to account for most of the quantitative genetic variation while allowing for outliers and intermediate populations. Some areas of the distribution may need further sampling to more accurately elucidate their racial affinities, especially those with traits of high economic importance.