Induction and characterization of tetraploids in Chinese Privet (Ligustrum sinense Lour.)

Abstract

Invasive plant species are a global issue impacting many local ecosystems and economies in the world. A large number of invasive plants were originally introduced as ornamentals. Developing genetic tools to reduce or eliminate invasiveness has become an important objective of ornamental plant breeding. This study intended to develop an effective technique to induce tetraploids, the critical and much needed genetic material for producing typically infertile triploids, thereby reducing the invasiveness of Ligustrum sinense, a species commonly used in the landscape in many parts of the world. Pure L. sinense tetraploid plants were inducted by applying colchicine to the shoot tips of emerging seedlings before true leaves emerged. Treatments with 0.1% or 0.2% colchicine resulted in higher frequencies of pure tetraploids (30.8%) and lower seedling mortality compared to higher concentrations (0.3% and 0.4%). Flow cytometry analysis showed that L. sinense tetraploids contained 4.67 pg/2C nuclear DNA content, 94.6% higher than that of its diploids. Compared to diploids, L. sinense tetraploids showed significant changes in morphology. Tetraploid plants were more compact and 25.4% shorter and had 20.1% fewer branches; their leaves were 48.0% larger and had 71.8% higher fresh and dry weight. Stomata on tetraploid leaves were 45.7% lower in density and 32.2% larger in size than those on diploid leaves. This study represents the first report of an effective technique for induction of pure tetraploids in this invasive species and characterization of nuclear DNA content and morphological changes from chromosome doubling. The availability of these puretetraploids in L. sinense will enable interploidy hybridization for production of infertile triploids for this common and highly desirable yet invasive ornamental species. Additionally, these tetraploids can facilitate investigation into tetraploidy-induced morphological changes and how they will impact L. sinense plant physiology and tolerance to abiotic stresses such as droughts.