Growth, straightness and survival at age 32 in a Pinus strobus x P. wallichiana F1 hybrid population (Experiment 2)

Abstract

By using an incomplete factorial mating design between twenty Pinus strobus L. female and seven P. wallichiana Jack. male trees, a number of 34 full-sib families were obtained. The objective of this experiment was to combine the fast growing of the former species with moderately to high resistance to blister rust (Cronartium ribicola Fich. in Rabenh.) of the latter one. The hybrid families were artificially inoculated at age two, and field planted at age four. The plantation took place within an old black current (Ribes nigrum L.) heavy infected by blister rust. In order to provoke new infections, this time naturally, the pine rows were planted in between the black currant ones. Diameters at breast height, tree height, tree growth rate volume, stem straightness and tree survivals were the traits measured at age 32 from seed. The first trial thinning was simultaneously applied with the present measurements. The average tree survival was 74.8% in hybrids, 8.3% in Pinus strobus and 27.8% in P. wallichiana. Highly significant (p < 0.01) differences were found between hybrid families for all traits except stem straightness. Genetic coefficient of variation at family level was 13.7% for tree volume growth rate and 15.9% for tree survival, but only 2.1% for tree straightness. Broad-sense family heritability estimates were 0.530 for diameter at breast height, 0.596 for stem height, and 0.564 for stem volume growth rate, 0.166 for stem straightness, and 0.539 for tree survivals. Similarly, the individual tree narrow-sense heritability estimates were 0.138 for diameter at breast height, 0.209 for stem height, 0.149 for stem volume growth rate, and 0.022 for stem straightness. If the best 5, 10 and 15 of 34 families were selected, a genetic gain of 17.7%, 13.4% and 10.2%, respectively, may be achieved in tree survival or blister rust resistance. Similarly, if the best 5%, 10% and 15% individuals within the best hybrid families were selected, a genetic gain of 4.7%, 4.0% and 3.6% in diameter at breast height and 10.7%, 9.1% and 8.1% in tree volume growth rate could be made. The estimated genetic gains indicated that a program aimed at improving growth traits and survival through interspecific hybridization could be successfully achieved.