Abstract:

Objective: The aim of this study is to investigate the adaptation of seedling traits in the progeny of poplar hybrids under low nitrogen stress, and to screen for excellent genotypes with strong low nitrogen tolerance, in order to provide theoretical basis for breeding new poplar varieties with fast growth and strong adaptability to low nitrogen environment. Method: Using the potting method in greenhouse, a total of 226 hybrids from the crossing between Populus simonigra and P. nigra were used as experimental material to determine growth, leaf morphology, chlorophyll fluorescence parameters and nitrogen isotope parameters traits under low nitrogen (LN) and normal nitrogen (NN) treatments. The Restricted Maximum Likelihood/Best Linear Unbiased Prediction (REML/BLUP) based on the linear mixed model was used to analyze genetic variation and the estimation of genetic parameters including breeding values. The multi-trait selection based multi-trait genotype-ideotype distance index (MGIDI) was used to rank the genotypes of the hybrid progeny and to comprehensively evaluate the adaptability of the hybrid progeny to the experiment. Result: The mean values of growth and leaf morphological traits differed significantly between the two groups of N supply levels, with LN﹤NN. For most of these above traits, the genotype effects were significant among the progeny, and the interaction effect (G × E) between genotype and nitrogen-supplying treatment environment was extremely significant, whereas neither genotype effects nor G × E effects were significant for chlorophyll fluorescence parameters. Broad sense heritability ($ {h}_{\mathrm{g}}^{2} $), mean heritability ($ {h}_{\mathrm{g}\mathrm{m}}^{2} $), and coefficient of genetic variation (CV_g) of the traits were less than 0.38, 0.56 and 22.30%, respectively. The principal component analysis (PCA) was conducted on the breeding values of growth and morphological traits, as well as the observed values of nitrogen isotope parameters. The first four principal components (FA) with their eigenvalues above 1 were extracted for factor analysis, accounting for 84.10% of total variance. The four factors (FA1, FA2, FA3 and FA4) of the factor analysis reflected the information on growth, leaf morphology, nitrogen isotope composition and nitrogen isotope content, respectively. The multi-trait index, MGIDI, was obtained to rank the genotypes of the progeny. The top 42 genotypes of the progeny were selected at a selection intensity of 20% with genetic gains for the traits ranging from 2.0% to 16.50%, of which 7, 8, 7 and 3 genotypes showed dominance for growth, leaf morphology, nitrogen isotope combinations and nitrogen isotope content, respectively. Conclusion: The seedling growth, leaf morphology and physiological traits of the poplar hybrid progeny are significantly inhibited under low nitrogen stress. The growth traits and leaf morphological characteristics are significantly influenced by genetic factors and their interactions with the environment. The genotypes selected by the comprehensive evaluation of multiple trait indices have strong adaptation to low nitrogen stress and can be used for selection of new poplar varieties with low nitrogen tolerance.

Key words: Populus spp., low nitrogen, BLUP, breeding value, MGIDI, multi-trait selection