Growth, straightness and survival at age 32 in a Pinus strobus x P. wallichiana F1 hybrid population (Experiment 1)

Abstract

An interspecific factorial hybridization was made, where seven P. strobus female parent trees were mated to four P. wallichiana male trees, in order to transfer genes for resistance to blister-rust from the blue pine to the F1 hybrids. The hybrid seedlings and the open pollinated families of the two parents were three times consecutively inoculated with blister-rust. The six years old seedlings were transplanted in the fi eld in the so called Valiug Experiment 1. The experimental design consisted in 28 hybrid full-sib families and two open pollinated families of the parent species. Plantation took place in a complete randomized block design with three blocks, with 6 to 12 seedlings per linear plot and 3 x 3 m spacing. This paper is based on the measurements made at age 32, just after the fi rst thinning. Diameter at breast height, tree height, tree volume, stem straightness and tree survival were the fi ve measured traits. According to ANOVA, signifi cant (p < 0.05) and highly signifi cant (p < 0.001) differences for diameter at breast height, tree height, volume growth rate, stem straightness and tree survival were detected between hybrid families. Highly signifi cant (p< 0.01, p < 0.001) differences were found between eastern white pine female parents for survival, stem straightness and all growth traits, suggesting that nuclear additive genes are controlling the respective characters. Consequently, high survival or genetic resistance to blister-rust can be found within the P. strobus species even though it is highly susceptible to this pathogen. The P. wallichiana parents exhibited signifi cant additive effects on straightness and breast height diameter, but no signifi cance in height, volume, and tree survival. The contribution of the additive variance to the phenotypic one was 65.7% for diameter, 58.6% for height, 50.5% for volume, 70.4% for stem straightness and 73.4% for tree survival. Hence, additive variance should be employed in a breeding program. The narrow-sense family heritability estimates were 0.657 for diameter, 0.586 for height, 0.505 for volume, 0.705 for stem straightness and 0.734 for tree survival. The individual-tree narrow-sense heritability estimates were 0.336 for diameter, 0.253 for height, 0.205 for volume and 0.121 for stem straightness. Assuming selection of 5, 10, or 15 families out of the 28 tested ones and sexual propagation, a genetic gain of 9.5%, 6.8% and 4.8% in diameter, and 11.2%, 8.1% and 5.7% in volume and 16.4%, 11.8% and 8.4% in tree survival, respectively, might be achieved. Selecting the most outstanding 5%, 10%, or 15% individual F1 hybrids would yield a genetic progress of 9.7%, 8.3% and 7,4% in diameter and 10.2%, 8.8% and 7.8% in volume growth rate. The hybrid population mean surpassed in tree survival the open pollinated eastern white pine mean by 70.7% while the eastern white pine, surpassed the hybrid in all growth traits. The F1 hybrid and P. strobus open pollinated parent species averaged 0.993 and 1.069 m3 volume per tree, respectively. By extrapolation the yield results from the hybrid trial area to 1 ha results in a yield of 559.9 m3 per hectare for hybrids and 602.5 m3 for P. strobus female parent species. In conclusion, hybrids should be taken into consideration and used in plantation programs in high-blister-rust-hazard areas.