Objective  This study aims to explore the variation of fruit phenotypic traits of the wild Amygdalus mira populations in Tibet of southwestern China and to screen the good germplasm resources by the principal component analysis, and also to ascertain the effects of ecological factors on phenotypic traits of fruits for fine breeding and generalizing of Amygdalus mira.

  Method  The 18 populations (SYD, AR, LD, JT, DB, QD, MX, LK, BM, GY, SZ, BJ, ZR, PZ, QN, BH, LZ, CN) in 5 regions were surveyed and sampled according to the concentration distribution area combined with the differences in altitude, climate and maturity of wild A. mira in Tibet. In each population, 13 trees with good growth potential were selected, and the spacing of each individual plant was greater than 50 m. The ripe fruits were collected from the dark, sunny and the upper, lower four directions of each plant, 5 fruits were randomly selected from each direction, 20 in total, and then the phenotypic traits were measured.

  Result  The fruit phenotypic traits were highly significantly different in population and among populations of A. mira. The mean of phenotypic differentiation coefficient was 67.99%, and the fruit phenotypic variations were mainly derived from populations. According to the results of PCA analysis and the use of pulp and core, the representative populations with large fruit, small nut, thick pulp and low nuclear rate were selected, and they were the Jiangtang Township, Qiangna Township and Lang Township. While the representative populations with small fruit, large nut, thin pulp and high nuclear rate were the Guyu Township, Shangyadong Township and Qudeng Township. The 5 ecological factors explained 56.00% of the fruit character variation through RDA analysis, and only the annual average temperature had a significant effect on the overall variation of fruit traits (P = 0.049). The multiple regression equation of the two characteristics of the pulp thickness and the nuclear rate with the ecological factors were all significant (P < 0.01), and the adjusted R² was 0.5993 and 0.7981, respectively. The thickness of pulp was negatively correlated with longitude, altitude and average annual rainfall, and was positively correlated with latitude and average annual temperature. The nuclear rate was positively correlated with longitude, altitude, average annual rainfall and annual temperature, and was negatively correlated with latitude. The effects of longitude, latitude and altitude on the thickness of pulp and the nuclear rate were highly significant.

  Conclusion  The phenotypic variation of A. mira mainly comes from populations. According to the phenotypic traits, fruit type and nut type of A. mira and its representative populations were screened. The effects of longitude, latitude and altitude of 5 ecological factors on the thickness of pulp and the nuclear rate were the most significant.