Development of Colchicine-Induced Tretraploid St. Augustinegrass.

The base chromosome number of Stenotaphrum secundatum (Walt.) Kuntze,  is x=9, with diploids (2n=2x=18), triploids (2n=3x=27), and tetraploids (2n=4x=36) reported. Polyploid lines of St. Augustinegrass have been found to be more resistant than diploids against several biotic stresses including chinch bugs and sting nematodes. Polyploids were also reported to exhibit increased water-use efficiency as compared to diploids. The exploitation of the variation found among polyploids has been hindered due to sterility issues related to unbalanced chromosome compliments, however. The present study was conducted to develop tetraploid St. Augustinegrass lines of cultivar 'Raleigh' in order to investigate if they can be more readily crossed with polyploid genoytpes of interest. Seeds of Raleigh were treated with four colchicine treatments. Seedlings recovered after treatment were screened for genome size changes using flow cytometry. A set of putative tetraploids was identified and corroborated through chromosome counts. Further evaluation of these lines for fertility levels is needed before evaluating their potential for crosses.