Detection and verification of quantitative trait loci for resistance to Dothistroma needle blight in Pinus radiata

Six related radiata pine ( Pinus radiata) full-sib families were used to detect and independently verify quantitative trait loci (QTLs) for resistance to Dothistroma needle blight, caused by Dothistroma septospora. The detection families had from 26 to 30 individuals each, and had either a common maternal (31053) or paternal (31032) parent; one family (cross 4) consisted of progeny from both parents, 31053 x 31032. Approximately 200 additional progeny from cross 4 were clonally replicated and planted at two sites, with at least five to seven ramets of each individual per site. Marker segregation data were collected from a total of 250 RFLP and microsatellite markers, and single factor ANOVAs were conducted separately for each family and marker. A number of putative associations were observed, some across more than one family. Permutation tests were used to confirm expected probabilities of multiple associations based on chance alone. Seven markers representing at least four QTLs for resistance to Dothistroma were identified as being significant in more than one family; one of these was significant at P<0.05 in three families and highly significant at P<0.01 in a fourth. Further confirmation was obtained by testing those markers that were significant in more than one of the detection families (or highly significant in cross 4) in the clonally replicated progeny from cross 4. Four QTL positions were verified in the clonal populations, with a total percent variation accounted for of 12.5.