我国桉树遗传育种研究进展

桃金娘科(Myrtaceae)桉属(Eucalyptus)、杯果木属(Angophora)和伞房属(Corymbia)树种统称桉树,引入我国已有130余年的历史,是重要的工业用材林树种。我国桉树遗传育种研究始于20世纪60年代的种子园建设和70年代后期的种源试验,一些技术显著促进了其进程,主要有:①早期的种子园技术促进了无性繁殖困难树种的有性扩繁;②20世纪90年代兴起的扦插和组织培养技术推动了优良无性系选育与应用;③20世纪90年代末分子标记技术开启了我国桉树分子育种研究的新纪元;④21世纪初转基因技术为品种创制提供了崭新的手段;⑤刚尝试的基因组编辑技术展现了巨大的应用潜力。桉树育种策略和种质资源是其遗传育种研究的基础,已对一些树种制定了育种策略和育种计划,兼顾纯种内轮回选择和杂种无性系的选育,主要经济性状包括材积生长、木材密度、抗病虫和抗风等;累计已收集了近200个树种3 000余个家系的种质资源。我国桉树遗传育种研究已取得显著进展,主要包括:①几个主要树种的轮回选择和世代改良,仅尾叶桉(E. urophylla)进入了第3个世代;②杂交育种的成效显著,培育了目前仍主栽的DH32-29和DH33-27等优良杂种无性系;③无性系育种结合无性繁殖技术(尤其是组织培养)的研发,极大地推动了无性系林业的发展;④开发了多种分子标记,包括基于新一代测序技术的标记,并基于分子标记利用连锁作图和关联分析的方法,在尾叶桉等6个树种中检测了与生长、材性和/或抗逆等性状相关的基因组位点;⑤已对逆境响应、激素和木材形成等相关的功能基因进行了克隆和表达分析,一些功能基因显示了较好的育种应用潜力;⑥已优化遗传转化体系,获得了转基因植株,并尝试了基因组编辑的可行性。但是,我国桉树遗传育种研究仍面临诸多挑战,如基因型×环境互作的复杂性和高质量基因组/泛基因组的缺乏,种质资源流失,新无性系缺乏,尚待从头克隆和鉴定具有育种价值的优异基因,基因组选择实用性有待探索,遗传转化率需进一步提高等。桉树遗传育种研究对促进我国林业生产的意义是显著的,将有望在高世代改良、种质资源的长期评价、杂种优势的机制与利用、基因组选择的有效应用和转基因与基因组编辑技术等方面取得突破。

Progresses of eucalypt genetics and breeding studies in China

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.