Herbicide-tolerant Zoysia grass (Zoysia japonica Steud.) has been generated previously through Agrobacterium tumefaciens-mediated transformation. The genetically modified (GM) Zoysia grass survived Basta spraying and grew to maturity normally while the wild-type (WT) grass stopped growing and died. GM Zoysia grass will permit more efficient weed control for various turf grass plantings such as home lawns, golf courses, and parks. We examined the environmental/biodiversity risks of herbicide-tolerant GM Zoysia before applying to regulatory agencies for approval for commercial release. The GM and WT Zoysia grass' substantial trait equivalence, ability to cross-pollinate, and gene flow in confined and unconfined test fields were selectively analyzed for environmental/biodiversity effects. No difference between GM and WT Zoysia grass in substantial traits was found. To assess the potential for cross-pollination and gene flow, a non-selective herbicide, Basta, was used. Results showed that unintended cross-pollination with and gene flow from GM Zoysia grass were not detected in neighboring weed species examined, but were observed in WT Zoysia grass (on average, 6% at proximity, 1.2% at a distance of 0.5 m and 0.12% at a radius of 3 m, and 0% at distances over 3 m). On the basis of these initial studies, we conclude that the GM Zoysia grass generated in our laboratory and tested in the Nam Jeju County field does not appear to pose a significant risk when cultivated outside of test fields.

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We have developed a genetically engineered herbicide-tolerant Zoysia grass with potential commercial value. However, the possible flow of genes to wild-type or neighboring plant species raises ecological and commercial concerns, although herbicide-tolerant GM Zoysia grass does not appear to pose a significant risk. One efficient way to prevent transgene escape in GM plants is to control fertility. Thus, we attempted to generate GM Zoysia mutants with defects in the development of reproductive organs, but that can be vegetatively propagated. To induce mutation, a range of γ-rays from 10 to 50 Gy, initially determined to be the optimal dose for inducing mutation, was used to irradiate GM Zoysia during the pollination stage. Notably, nine (4%) lines displayed defects in the floral transition from the vegetative to reproductive phase, while all nonirradiated GM Zoysia grasses developed normally. Under greenhouse conditions (natural light and temperature), these GM Zoysia lines have been vegetatively propagated for four years without forming reproductive structures. This technology could also be applied in other GM plants being cultivated through vegetative propagation, such as creeping bent grass.