Improvement of turfgrass quality by gamma ray irradiation in Stenotaphrum secundatum (Walt.) Kuntze

St. Augustinegrass, (Stenotaphrum secundatum (Walt.) Kuntze, a warm-season turfgrass, is commonly used for home lawns and public gardens where trees are dominant, in the United States due to superior shade tolerance and relatively low maintenance requirements. However, its coarse-leaf texture restricts wider use of this species. Therefore, there is a need for improved St. Augustinegrass cultivars that posses dwarf growth habits with finer leaf texture. Gamma ray irradiation has been used to induce variations in turfgrass breeding. Dwarfism is the most common mutant character obtained by induced mutation in plants. The objective of this study was to obtain mutant St. Augustine lines with finer texture and dwarf growth habit from a coarse ('G') and a very coarse textured ('M') germplasm introduced to Turkey many years ago with unknown origin. The stolon pieces of 'G' and 'M' genotypes were irradiated from 60 Co source with 20, 40, 80 or 120 and 50, 100, 150 or 300 Gy, respectively. Dosages of 102.54 and 94.96 Gy were determined to be LD 50 for the cuttings of 'G' and 'M' genotypes, respectively. Survival rate decreased linearly with increasing gamma rays. The 15 mutants (0.35 % of the irradiated plants) with altered morphological traits were identified among 4301 node cuttings by phenotypic selections. These mutant lines exhibited up to 65 % fewer stolon, 36 % shorter stolon, 29 % shorter leaf blade, 33 % shorter internode and 25 % shorter canopy height than parental genotypes. As a result, various morphological variations were obtained in both genotypes through mutagenesis. Results indicated the possibilty of developing improved St. Augustinegrass cultivars which are needed by greenkeepers/landscape arthitects to be used in shaded turf areas in warm season regions of Turkey through mutation breeding. Field performance of the elite mutant lines along with commercial St. Augustinegrass cultivars should be studied in a furher study. In the event that the mutant lines would have similar/superior turfgrass quality to commercial ones, use of St. Augustinegrass in target regions, especially in landscape areas under shade, is expected to increase significiantly.