Multi-Year Phenotypic Assessment and Genetic Selection in Progeny Trials of Liriodendron Hybrids

The conservation and genetic improvement of rare and endangered tree species are crucial for sustainable forest management. <i>Liriodendron chinense</i>, a relict species with limited distribution in China, exhibits high cross-compatibility with <i>Liriodendron tulipifera</i>, providing opportunities for interspecific hybrid breeding. In this study, 29 <i>Liriodendron</i> hybrids were established in a progeny trial plantation in Fujian Province, China, and subjected to multi-year evaluation of tree height, diameter at breast height (DBH), and individual stem volume. Significant differences (<i>p</i> < 0.01) among hybrids and hybrid × replicate interactions were detected for all traits across all assessment years, with individual stem volume showing the highest phenotypic coefficient of variation (35.30-40.56%). The mean annual increment in tree height increased during the early years, peaking at 1.50 m in the fourth year. Broad-sense and narrow-sense heritabilities for growth traits were consistently high (0.4073-0.7253 and 0.3410-0.6501, respectively), and the ratio of narrow-sense to broad-sense heritability ranged from 0.64 to 0.99, supporting the feasibility of early hybrid and individual selection. At a 10% selection intensity, hybrids No. 39, No. 59, and No. 74 were identified as elite, with selection based on individual stem volume providing the highest predictive accuracy and genetic gain (26.54-34.69%). Individual selection at a 1% intensity yielded genetic gains of 95.55-107.12% for stem volume. These results demonstrate substantial potential for early and efficient genetic improvement in <i>Liriodendron</i> hybrids, providing a theoretical foundation for the selection and deployment of elite hybrids and individuals in subtropical forest plantations.