2013 ASHS Annual Conference

Exotic woody ornamental plants are widely sold by the nursery industry and are considered to be a major source of invasive plants in the U.S. We have been utilizing induced or existing polyploids to create sterile types of nandina (Nandina domestica) and lantana (Lantana camara) for invasiveness reduction or elimination. All existing nandina cultivars were found to be diploids. Two chemicals were used to treat three types of nandina plant materials. When applied to growing shoots or germinating seeds, colchicine induced tetraploids. More than a dozen of solid tetraploid nandina plants have been obtained. Tetraploid nandina plants exhibited slight reduction in pollen stainability but much reduction in fruit production and seed germination. Some of the nandina tetraploids showed potential to be released as sterile cultivars. Polyploids (triploids to hexaploids) were found to be common in existing lantana cultivars. Many lantana polyploids, including some triploids and petaploids, were rather fertile and prolific in fruit and seed production. Extensive ploidy and molecular marker analysis of polyploids’ offspring revealed that the fertility of these polyploids resulted from the production of unreduced female gametes and/or apomictic seeds. With these two traits in lantana, even triploids and pentaploids can be highly fertile and produce large numbers of seeds. In order to obtain highly sterile triploid lantana, it was imperative to use tetraploids and diploids without the ability to produce unreduced female gametes and apomictic seeds. Hundreds of new lantana triploids have been generated and evaluated, and two new sterile, triploid lantana cultivars have been released. The male and female sterility of these triploid cultivars was high and stable when tested at multiple sites in Florida and grown side by side with fertile native lantana (Lantana depressa). More triploid lantana cultivars are expected to be released in the coming years. Our results indicate that polyploid induction or production followed by vigorous screening and evaluation is an effective approach to sterilizing some of the exotic invasive woody ornamental plants and developing sterile, non-invasive cultivars.