Objective This study aimed to investigate the variations on leaf and stomatal traits of long branch leaves in the full-sib diploid and triploid hybrids between sections Tacamahaca and Aigeiros of Populus, and to analyze the genotype and ploidy effects on the traits.

Method Cuttings of the full-sib diploid and triploid hybrids between P. pseudo-simonii × P. nigra ‘Zheyin3#’ and P. × beijingensis were randomly selected to investigate variations on leaf and stomatal traits of the long branch leaves.

Result The leaf length (LL), leaf width (LW), leaf length-width ratio (LWR), leaf area (LA), petiole length (PL), chlorophyll content (SPAD), stomatal length (SL), stomatal width (SW), and stomatal density (SD) exhibited highly significant differences among different genotypes. The coefficient of variations for each trait ranged from 8.54% to 36.20%, and their repeatability values of these traits ranged from 0.645 to 0.916, indicating that the leaf and stomatal traits were controlled by strong heredity. The SPAD, SL and SW of the triploid population were significantly higher than those of the diploid population, and the SD was significantly lower than that of diploids, but there were no significant differences in leaf traits between different ploidy levels. However, not all triploid genotypes showed better performance on these traits than diploids. The correlation analysis showed that LL, LW, LA and PL were significantly positively correlated with each other. The SPAD, SL and SW were also positively correlated with each other, but negatively correlated with SD. Further analysis showed that leaf traits, such as LL, LW, LA, and PL, were mainly affected by the genotype effect, which contributed 59.5%−76.8% of the variance contribution rate for these traits. The SPAD, SL, SW, and SD were mainly affected by the ploidy effect, and the variance contribution rate of the ploidy effect for these traits ranged from 46.0% to 78.0%.

Conclusion Leaf and stomatal traits of the long branch leaves in 5-month-old cuttings of the full-sib diploid and triploid hybrids between sects. Tacamahaca and Aigeiros of Populus are affected by both genotype and ploidy effects with different degrees. There are large variations in leaf and stomatal traits among genotypes, and not all triploids are excellent. Therefore, the idea of “large population, strong selection” should be adhered to allotriploid breeding program in Populus.