Knowledge about pollen viability is important when evaluating the risk of genetically modified (GM) plants. Here, staining via iodine potassium iodide (IKI) or triphenyl tetrazolium chloride (TTC) could not distinguish between live and dead pollen from Zoysia japonica. Therefore, to obtain a reliable assessment of such viability and longevity, we developed an optimum germination medium containing 20% sucrose and 50 ppm H 3 BO 3 . Pollen grains transferred to the germination medium at about 1000 hours had a germination rate of >90%. Pollen was most predominantly shed at approximately 1000 hours, with viability declining to nearly 0% at 1200 hours. All germinability was lost within 150 min when stored at 25°C. No significant difference was found between GM and non-GM plants in their pollen viability or longevity.

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.

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.

The 'Halla Green 7' cultivar is a hybrid of Zoysia matrella and Zoysia japonica. The inflorescences of Z. matrella lines were collected from Jeju Island near the border between Z. matrella and Z. japonica wild plants, respectively. After their harvest, the seeds were sown and various interspecific lines were obtained. In 2021, a line with greening period extending phenotype during the low temperatures of winter was registered under the cultivar name of 'Halla Green 7' (Registration No. 245). The main morphological characteristics of the 'Halla Green 7' variety are as follows: genetically short length of plant (12.2±0.58 cm), very wide angle of leaf (68.6°), short length of leaf blade (8.38±0.37 cm), medium-leaf (3.29±0.09 mm), and very low leaf sheath (2.18±0.19 cm). The short length of leaf sheath makes it easy to manage the turf grass with low height. A very wide leaf angle has a high photosynthetic efficiency. The 'Halla Green 7' cultivar is morphologically classified as Z. matrella × Z. japonica hybrid line by medium-width of leaf blade and the presence of trichomes on the leaf surface. The colors of the leaf blade, leaf sheath, and stolon are green, light green, and light purple, respectively. During the low temperature period of winter, chlorophyll content of the leaves of 'Halla Green 7' shows a 10.1-fold from that of the control Z. japonia 'Yaji' and about 4.2-fold from that of the control Z. matrella Zm-6. This greening period extending phenotype is expected to contribute to the industrialization of zoysiagrass (Registration No. 245).

Poa pratensis), 크리핑 벤트그라스(Agrostis stolonifera), 라이 그라스(Lolium perenne), 톨훼스큐(Festuca arundinacea) 등이 속하며, 난지형 잔디는 들잔디(Zoysia japonica), 금잔디(Zoysia matrella), 갯잔디(Zoysia sinica), 왕잔디(Zoysia macrostachya), 버뮤다그라스(Cynodon dactylon) 등이 있다(Kim & Lee 2010).