Development and Characterization of Colchicine-Induced Tetraploid Lines of St. Augustinegrass.

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] (2n = 2x = 18) is characterized by rapid stolon production which makes it well suited for sod production, home lawns and commercial landscapes. While many genotypes are cross-fertile, all St. Augustinegrass cultivars are propagated vegetatively in sod production. As a means of ensuring varietal purity, the development of sterile triploid hybrids by crossing tetraploid and diploid genotypes has been successfully used in other warm-season turfgrasses. Applying this model in St. Augustinegrass would be beneficial to sod producers and turf managers who require purity for certification and uniformity for performance, respectively. Therefore, the present study was conducted to develop colchicine-induced tetraploid lines of St. Augustinegrass. Seeds of cultivar ‘Raleigh’ were treated with four colchicine concentrations at four exposure times. Seedlings recovered after treatment, were screened for genome size changes using flow cytometry. A set of putative tetraploid lines was initially identified and evaluated for stomatal density, stomatal length and pollen stainability. Further analysis of putative tetraploids indicated all lines had found to be diploid with the exception of one, DSA 13005. Pollen stainability of this line was high and it produced 33 progenies through selfing, two of which were identified as putative tetraploids via flow cytometry. Average stomata lengths for DSA 13005 and its two progeny lines, DSA 16001 and DSA 16016, were found to significantly (P<0.05) larger than that of diploid control Raleigh. All three lines were corroborated as tetraploids (2n = 4x = 36) through chromosome counts. These lines will be used in future breeding efforts in an attempt to develop sterile triploid cultivars.