This study was carried out to develop new zoysiagrass (Zoysia japonica Steud.) cultivar ‘Halla Green 2’ (Grant number: No. 118). To develop a zoysiagrass cultivar with dwarfism by using the mutation breeding method, the wild type control "Gosan" plants were irradiated using a 30 Gy gamma ray source in 2010. Dwarf mutants were selected from the mutated grasses in successive generations. Dwarf mutant lines were identified and a new zoysiagrass variety Halla Green 2 was developed. The plant height of Halla Green 2 was 3.4 and 1.8 times lower than that of Gosan and Zenith, respectively. This cultivar has dwarf characteristics such as shorter sheath, shorter leaf blade, shorter flag leaf, and shorter third internode of stolon compared to those of Gosan and Zenith. Additionally, the sheaths and leaf blades color of Gosan, Zenith and Halla Green 2 were all light green, whereas their stolons were purple, yellow-green and yellow green, respectively. Trichomes(hairs) were visible on both adaxial and abaxial surfaces of the Gosan leaves, whereas only on the adaxial side of the Zenith and Halla Green 2 leaves. The Halla Green 2 grass showed distinguishable morphological traits compared to those of wild type Gosan and Zenith.

To develop a dwarf turfgrass (Zoysia japonica) cultivar with artificial mutation-induced breeding method, the wild type control "Gosan" plants were exposed to a 30 Gy gamma ray source in 2010. The mutant lines showing short height were selected from successive generations. One of the resulting dwarf lines obtained was registered under the cultivar name of “Halla Green 1” (2016). The dwarf phenotype of the Halla Green 1 includes a reduction of the height by 4.5-fold, an increase in leaf and third internode lengths by about 6- and 2.3-fold, respectively, compared to the Gosan, and approximately 2.4-, 3.8-, and 1.5-fold relative to the Zenith, respectively. In addition, the Halla Green 1 had a sheath of darker green coloring compared to the light green Gosan and Zenith. The leaf blades of Gosan, Zenith and Halla Green 1 were all light green, whereas their stolons were purple, yellow-green and light purple, respectively. Trichomes presented on both adaxial and abaxial surfaces of the Gosan’s leaves, and only on the adaxial side of the Zenith’s leaves, but none on the Halla Green 1 leaves. The Halla Green 1 exhibited sufficiently distinct morphological traits when compared with the wild type Gosan and Zenith that the dwarf phenotype enhances its commercial viability.

Daily shedding pattern and longevity of pollen are important consideration for the evaluation of gene flow of transgenic plants. During the day, the pollen shedding pattern of zoysiagrass was determined in the lawn by using a device to collect airborne pollen on a glass slide, resulting that the pollen grains were released predominantly between 7:00 and 9:00. The result was also supported by in vitro pollen germination test, which was performed with pollens collected from 1:00 through 24:00 at 1h interval. Influence of temperature and humidity on pollen longevity was determined by germinating pollen at 25°C after incubating them for 10, 30, 60, and 180 min under different temperatures and humidity with pollen of zoysiagrass that opened freshly at about 9:00. The result showed that pollen longevity of zoysiagrass was sensitive to change of temperature and humidity and longest under the temperture and humidity of 15-20°C and 80-99%, respectively. Under natural conditions with the same method as upper controlled conditions, was determined pollen longevity. Under sunny atmospheric conditions, pollen longevity decreased to 20% in 60 min, with a complete extinction in 120 min. Under cloudy atmospheric conditions, pollen remained viable up to 450 min, with about 20% longevity after 360 min. No significant difference was found between GM and non-GM plants in their pollen longevity.