Results after 19 years of testing in a Pinus strobus x P. wallichiana F1 hybrid population

Abstract

Full-sib families were generated from a factorial design between seven female trees of P. strobus and four male trees of P. wallichiana to combine the rapid growth of former species with high resistance to blisterrust (Cronartium ribicola) of the latter one. At age two the hybrid families were artificially inoculated with blister-rust and at age six theywere field planted. Total height growth, diameter at 1.3 m, basal area, stem volume, stem straightness and tree survival were measuredat age 19 after planting. Significant (p<0.05) and highly significant (p<0.01; p<0.001) differences among female effects were found for all tested traits including survival suggesting that nuclear additive genescontrolled these traits. Male effects were significant only for stem straightness. In all but one trait the σ2GCA: σ2SCA and σ2GCA-F : σ2GCA-M ratios were in favour of additive variance suggestingthat this variance should be used in the breeding strategy. Narrow-sense heritability at family level was 0.778 for volume growth rateand 0.861 for survival; such high values indicate that the breeding programme, has good chances of success. Two of the 11 tested parentsexhibited significant positive g.c.a. effects for survival after heavy blister-rust inoculation. One parent exhibited highly significantpositive g.c.a. effects for volume growth rate. The three good general combiners should be taken into account in the breeding programme.Estimate of the high-parent heterosis was negative for the volume but positive for survival. For volume, the hybrid mean was 5.9% lowerthan the mean of the eastern white pine but 85.4% greater than blue pine bulk lot for survival. Estimate of low-parent heterosis for survivalwas also positive; i. e. the hybrid population mean was 537.5% greater than eastern white pine. If the hybrids will be used in operationalplanting programs, a variable genetic gain between 6.0 and 10.5% for volume and between 6.8 and 9.6% for survival could beachieved.