Analysis of Genetic Variation and Evaluation of Early Selection in Picea crassifolia Based on Different Forest Ages

To elucidate the patterns of genetic variation in growth traits of Picea crassifolia half-sibling families and to screen superior materials,This study systematically analyzed variance components, genetic parameters, and age–age correlations for growth traits (tree height, diameter at breast height/ground diameter, current shoot length, crown width, and volume) in a progeny test plantation comprising 113 open-pollinated P. crassifolia families aged 5 to 17 years. Elite family and individual selection were subsequently conducted. Results showed significant or highly significant differences among families for all traits. Tree height exhibited the highest family variance components across all ages (49.98%～65.88%), with error variance consistently decreasing with age (44.68%～33.47%), indicating the most stable genetic control. In contrast, diameter growth was dominated by error variance (57.64%～67.54%) and was significantly influenced by environmental factors. Current shoot length showed moderate genetic control, while crown width and volume were strongly affected by genotype × environment interactions. Family heritability for tree height ranged from 0.84 to 0.92, compared to individual heritability of 0.21～0.43; for diameter, family heritability ranged from 0.78 to 0.88, with individual heritability of 0.18～0.32. Age–age correlation analysis indicated that selection reliability at age 11 reached 88.2%, with a correlation coefficient exceeding 0.90 with age 17, establishing age 11 as the earliest reliable selection age. Using a 5% selection rate, six elite families were selected, achieving a realized gain of 18.26% and a genetic gain of 16.25% for tree height. By integrating membership function values, principal component comprehensive scores, and index selection, 38 elite individuals were selected (mean height 683.95 cm), achieving a tree height genetic gain of 40.85%, with an overlap exceeding 80% among the three methods. Therefore, tree height should be used as the core selection trait in P. crassifolia breeding. The selected elite families and individuals can serve as core parents for advanced-generation breeding. For P. crassifolia families, age 11 and above is recommended as the suitable age for early selection and variety certification.