Heredity analysis on combining ability and the selection of breeding parents of Eucalyptus hybrids

Relatively few studies have been conducted on two-row mating design and fitness analysis of Eucalyptus hybrids. Therefore, in this study, double-row hybridization was conducted among six species of Eucalyptus pellita (P), Eucalyptus wetarensis (W), Eucalyptus urophylla (U), Eucalyptus grandis (G), Eucalyptus tereticornis (T), and Eucalyptus cameldulensis (C) in a two-row hybridization to explore the relationship between the progeny and the parents through the genetic analysis of fitness, and to provide excellent and stable genetic materials for the selection of parents for subsequent hybrid breeding, the establishment of seed gardens, and the asexual propagation of excellent monocultures.

A 3×6 irregular diallel crossing of Eucalyptus hybrids was used for genetic analysis, selections of parents and hybrid combinations about growth characteristics of two years of hybrids.

The growth of hybrid combinations varies greatly, and the growth performance was relatively stable, and the fast-growing performance of the two year old hybridization was outstanding. Among the males, the two year old hybridizations differed highly significantly (P < 0.01) for each trait, while the one year old hybridizations differed significantly (P < 0.05) only for the tree height trait, while the differences for the other traits were not significant (P > 0.05). Among the females, the two year old hybridizations differed highly significantly (P < 0.01) for each trait, while the one year old hybridizations differed significantly (P < 0.05) only for the tree height trait, while the differences for the other traits were not significant (P > 0.05). Among the males, there were highly significant differences (P < 0.01) in all traits in the one year old and two year old hybridizations. The analysis of genetic parameters showed that the narrow sense heritability of growth traits in hybrid combinations ranged from 0.153 4 to 0.194 3 and the broad sense heritability ranged from 0.178 5 to 0.247 2, and that the growth traits of Eucalyptus hybrid combinations were controlled by both additive and non-additive genes, and that in the case of additive genes, the influence of the male was stronger than that of the female parent. The fitness analysis showed that in the Eucalyptus hybrid combinations of the two years, the general combining ability (GCA) of the female W was the largest, followed by the female P, and the GCA of the parents U, C, T, and G was positive.

Different hybrids have different degrees of parental line effects at different growth stages, and the final selection of good hybrid combinations were W×C, P×U, W×T.