Abstract:

Eucalypts are the common name for trees from the three genera Eucalyptus, Angophora and Corymbia within family Myrtaceae. They have been introduced into China for more than 130 years and are currently an important choice of trees for industrial plantations. In China, genetics and breeding studies of eucalypts began with seed orchard establishment in the 1960s, followed by provenance trials in the late 1970s. Since then, some important techniques have shown significant impacts on accelerating the genetics and breeding studies of eucalypts, mainly including: (1) seed orchard management, especially in the early years, which has promoted the sexual propagation of those eucalypt species with difficulty in vegetative propagation; (2) cutting and tissue culture developed in the 1990s that have enhanced the selection and cultivation of superior clones; (3) molecular markers arisen in the late 1990s that have started the new era of eucalypt molecular breeding; (4) genetic transformation initiated in the 2000s that has provided a novel approach for creating new varieties; and (5) genome editing that is under attempt and has casted great application potentials. As breeding strategy and germplasm are concerned, breeding strategies and breeding plans have formulated for several species, in which within-species recurrent selection and hybrid clone selection were taken into account on such economic traits as volume growth, wood density, pest and disease resistance and typhoon tolerance; and more than 3 000 families of about 200 species collected for germplasm conservation. Great progresses have been made in eucalypt genetics and breeding studies in China, mainly including: (1) recurrent selection over generations accomplished for major species, with only E. urophylla reaching the third generation; (2) hybrid breeding with achievements of such widely planted hybrid clones as DH32-29 and DH33-27; (3) clonal breeding plus vegetative propagation technique development for tremendous contribution to clonal forestry; (4) development of several types of molecular markers, including the next-generation sequencing based markers, and marker-based delineation of genomic loci linked/associated with growth, wood properties and/or stress response detected in E. urophylla and other five species; (5) genes cloned and expression analyzed for stress response, phytohormone and wood formation, including some with promising application potentials; and (6) optimization of genetic transformation system, successful production of transgenic plants and attempt of genome editing. Nevertheless, some challenges remain herein, including genotype × environment interaction complexity and high-quality genome and pan-genome sequence absence as well as germplasm erosion, new clone scarcity, few de novo cloned genes with breeding values, genomic selection uncertainty and further upgrading of genetic transformation technology. Eucalypt genetics and breeding studies have played a pivotal role in China’s forestry development, and breakthrough may be made in advanced generation improvement, long-term germplasm evaluation, heterosis mechanism exploration and utilization, genomic selection application and trans-genic and genome editing techniques.

Key words: eucalypts, genetics and breeding, advanced generation, hybrid clone, molecular breeding, genetic transformation