Effect of fertilization and genetic variation on susceptibility of Pinus radiata seedlings to Hylobius abietis damage

The effects of establishment fertilization and pine genotype on pine weevil (Hylobius abietis L.) damage was studied in a radiata pine (Pinus radiata D. Don) naturally infected familya x fertilization genetic trial in Galicia (northwestern Spain). Fertilization strongly increased both growth and H. abietis damage, especially when calcium phosphate was included in the fertilization treatment. Fertilized plants showed higher degree of debarking, greater leader loss, and higher mortality than unfertilized controls. Because of the greater leader loss, fertilization did not significantly increase the actual height (height of live stem) 1 year after planting. In contrast, after the second growing season, fertilized plants overcompensated for the weevil damage and reached greater height than the unfertilized controls. However, considering the effects on survival and the stem deformities resulting from the leader losses, fertilization should be avoided (or delayed) in P. radiata plantations on clear-cut coniferous areas if the risk of H. abietis is high. Our results also indicate a strong genetic variation in H. abietis susceptibility within the Galician P. radiata breeding population. The high family-mean and the moderate individual-tree heritability estimates suggest that improving resistance to this pest by conventional breeding techniques is possible. The use of planting stock with improved resistance should be considered as another prophylactic measure to supplement the traditional methods employed against this pest.