Study of variation in the growth, photosynthesis, and content of secondary metabolites in Eucommia triploids

Key message Triploid breeding is a very effective method for genetic improvement of plants similar to Eucommia ulmoides that cannot be obtained through heterosis by distant crosses. Abstract Triploid breeding is an effective method for plant genetic improvement because it usually has stronger vegetative growth vigor than diploids. In this study, the growth, leaf area, secondary metabolites, and photosynthetic characteristics of Eucommia triploids obtained from high temperature-induced Eucommia megaspore chromosome doubling and 1-year-old diploid clonal plants were studied. The results showed that Eucommia triploids showed some advantages in vegetative growth, leaf traits, photosynthetic rate, and secondary metabolites compared with the diploid plants, and the variation amplitude of the triploids was greater than that of the diploids. Eucommia triploid individuals differed in the amount of growth and leaf secondary metabolic content. In addition, there were some differences in the average height and diameter of the triploid plants at a breast height of 2.41 m and 1.4 cm, respectively; these values were 16.99% and 19.09% higher than the diploid controls, respectively. The average leaf area of the triploids reached 280.36 cm 2 , and the leaf thickness was 449.43 µm, which exceeded 45.8% and 27.8% of the average of the diploid controls, respectively. The average triploid leaf size and photosynthetic rate were higher than those of the diploid control plants, which is the intrinsic reason for the growth advantage of the Eucommia triploid. The average contents of chlorogenic acid, aucubin, geniposide, and geniposidic acid in the triploid leaves were 10.20%, 1.34%, 118.22%, and 22.04% higher than those in the diploid controls, respectively. The results showed that triploidy breeding has great potential for the development and utilization of Eucommia ulmoides that cannot be obtained through heterosis by distant crosses.