Genetic dissection of fusiform rust and pitch canker disease traits in loblolly pine

Loblolly pine (Pinus taeda L.) exhibits genetic resistance to fusiform rust disease (incited by the biotrophic fungus, Cronartium quercuum f. sp. fusiforme) and pitch canker disease (incited by the necrotrophic fungus, Fusarium circinatum). In this study, a total of 14,015 loblolly pine cuttings from 1,065 clones were screened in controlled greenhouse conditions to identify phenotypes of clones, families, and parents that guide a genetic dissection of disease traits associated with pitch canker and fusiform rust. A total of 23,373 phenotypic data points were collected for lesion length (pitch canker) and gall score, gall length, and gall width (fusiform rust). We verified heritable fusiform rust and pitch canker traits and calculated parental, clonal, and full-sib family rankings for both diseases. Genetic correlations revealed that traits associated with fusiform rust are genetically distinct from one another, and that the genetic mechanisms underlying pitch canker and fusiform rust resistance are independent. The disease phenotyping described here is a critical step towards identifying specific loci and alleles associated with fusiform rust and pitch canker resistance.