An economic analysis and seed yield assessment of alternative breeding strategies in a white spruce tree improvement program

Abstract

Tree improvement programs in Alberta have been primarily based on selections from open-pollinated wild stand trees, without systematic breeding of elite parents through controlled pollination. This strategy has resulted in relatively slow advancements in genetic gain in most programs, given their age. Our objective was to compare seed yield, genetic parameters, and economic implications of three different breeding strategies to advance Alberta’s white spruce (Picea glauca (Moench) Voss) improvement programs. Eighteen genotypes, identified as ‘elite’ based on height breeding values (BV), were selected from a first-generation white spruce orchard and controlled crosses (CC) and controlled polymix (PM) crosses performed to compare seed yield and genetic parameters with open-pollinated (OP) seedlots from the same parent. Results show, that on average, OP seedlots had 29 seeds/cone and weighed 2.7 grams/1000 seeds, significantly larger than the CC seedlots with a mean of 10 seeds/cone and 2.2 g/1000 seeds. Polymix crosses produced intermediate mean values with 19 seeds/cone and 2.5 g/1000 seeds and were not significantly different from the other two breeding strategies. No statistical differences were found for cone length or germination percentage among the CC, PM, and OP breeding strategies. Significant phenotypic variability was found for seeds/cone (yield) and seed weight among families from CC, and these traits had moderate narrow-sense heritabilities of 0.49 (±0.11) and 0.29 (±0.13), respectively. There was no significant correlation between the general combining ability (GCA) of seed yield and BV for seedling growth, but females F132, F138, and F927 and males M966, M1002, and M1045 showed the best performance in seed yield and growth and would be good candidates to include in future controlled crosses. If CC breeding is considered a strategy for operational seed production, as conducted elsewhere, the highest land expectation value (LEV) was $141 CAD/ha at age 60, and the best net present values (NPV) were for both discount rates (2%, 4%) with log prices ($90 CAD/m3, $200 CAD/m3) tested. However, this advantage of CC vs PM and OP only occurred on the highest quality sites (i.e., Site Index (SI) 13 and 18). On the low-productivity site (SI = 6), with the various scenarios, improved material did not show any financial benefit. Our results show that seeds produced from the controlled crosses breeding strategy were inferior to those produced from the controlled polymix and open-pollinated strategies. However, with sufficient investment and company support, the CC breeding strategy could be used as a cost-effective method to increase genetic gain and advance white spruce breeding programs in Alberta.