Quantitative trait loci (QTLs) for intumescence severity in Eucalyptus globulus and validation of QTL detection based on phenotyping using open-pollinated families of a mapping population

Intumescence is a nonpathogenic physiological disorder characterized by leaf blistering. This disorder can affect growth and development in glasshouses and growth chambers and may be confused with pathogenic diseases. We used quantitative trait loci (QTL) analysis to examine the genetic basis of variation in intumescence severity in Eucalyptus globulus, and test for colocation with previously detected QTLs for pathogen susceptibility. QTL analysis used the phenotype means of open-pollinated (OP) families of an outcrossed F₂ mapping family (OP F₃; n = 300) of E. globulus and the linkage map constructed in the F₂. We validate this phenotyping approach for QTL analysis by assessing a trait previously used for QTL discovery in the F₂ and showing the same major QTL was detected with the OP F₃. For intumescence severity, five putative QTLs were detected across four linkage groups. Four of these did not colocate with previously reported QTLs for fungal pathogen susceptibility in Eucalyptus, suggesting the mechanisms underlying susceptibility to intumescence and to the two fungal pathogens are largely independent. This study demonstrates there is a genetic basis for variation in intumescence severity, reports the first QTL for intumescence severity in plants, and provides a robust framework for investigating the potential mechanisms involved.