Weevil resistance of progeny derived from putatively resistant and susceptible interior spruce parents

Abstract

Controlled-cross progeny of interior spruce ( Picea glauca (Moench) Voss × Picea engelmanni Parry ex Engelm.) parents ranked as resistant or susceptible to the white pine weevil, Pissodes strobi (Peck) were screened for resistance to the same insect by augmentation of the trial site with weevils. Progeny from two resistant parents (R × R progeny) sustained significantly fewer weevil attacks (13% of the trees were attacked) in the year following the augmentation, than progeny from susceptible parents (S × S progeny) (68% of the trees were attacked). Progeny obtained by crossing one resistant and one susceptible parent (R × S progeny) sustained intermediate attack levels (47% were attacked). Characteristics of the bark resin canals of the crosses were explored using microscopy techniques. Bark resin canal density was highest in R × R progeny, lowest in S × S progeny and intermediate in R × S progeny. There was a negative correlation between the percentage of trees attacked in each cross and the average density of the outer resin canals for each cross. A discriminant function was developed that distinguished between resistant and susceptible progeny using bark characteristics. The function was characterized by positive coefficients for outer resin canal density and inner resin canal size, and a negative coefficient for bark thickness. Thus, trees with thin bark, large inner resin canals and dense outer resin canals are more likely to be resistant to P. strobi.