Molecular dissection of growth, vegetative phase change, pest resistance, wood properties, and their interactions in Eucalyptus globulus
QTL analysis based on clonally replicated F2 progeny allowed dissection of the complex interactions that exist between disease severity, vegetative phase change, and the negative genetic relationship between growth and wood density. We used an outbred, F2 family derived from an inter-provenance cross in Eucalyptus globulus. The grandparents were from widely separated locations in Tasmania and differentiated by numerous quantitative traits. Maps of the maternal and paternal parent were created from 112 progeny and merged into a consensus containing 169 markers (34 SSR and 135 AFLP loci) in 11 linkage groups. The progeny were cloned and planted in a randomised field trial containing two trees (ortet or ramets) per genotype in 1998. We assessed damage caused by Mycosphaerella leaf disease and autumn gum moth, which occurred shortly after planting and before vegetative phase change. Growth and phase change were monitored annually for 7 years and wood density was assessed using 12mm stem cores in the last year. The F2 was genetically variable, with significant differences detected amongst genotypes for all traits. Significant QTL were detected for growth, height to phase change, Mycosphaerella damage and wood density. Two unlinked QTL explained up to 51% of the phenotypic variance in Mycosphaerella severity. The QTL for height to phase change that explained 17% of phenotypic variation, was co-located with one of the QTL for Mycosphaerella severity, however no significant correlation between these traits was detected. Early growth and Mycosphaerella severity were negatively correlated, but the QTL for these traits were not co-located with each other or the two QTL for wood density.