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Title: Selection for freezing tolerance in St. Augustine grass under controlled conditions

item LI, RUYU
item Livingston, David

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2009
Publication Date: 8/8/2010
Citation: Li, R., Qu, R., Bruneau, A., Livingston, D.P. 2010. Selection for freezing tolerance in St. Augustine grass under controlled conditions. Crop Science. 129:417-421.

Interpretive Summary: St Augustinegrass is a widely used grass for lawns in southernmost states in the US. It ability to tolerate shade and low moisture make it a good option for home owners. However, its susceptibility to freezing temperatures in the winter make its cultivation north of about the middle of the state of North Carolina a tenuous prospect. A protocol was developed that would identify more freezing tolerant germplasm. Acclimating conditions that were best suited to determining freezing tolerance were one week at 13°C followed by a second week at 3°C and then freezing from -3 to -5°C. In this project we used 2 sources of germplasm: 1) existing collections and 2) natural variation that arises from tissue. These tests found that one line (Elm4) was more freezing tolerant than the existing winter hardy cultivar Raleigh. In addition, a single genotype out of 7800 plants that was derived through natural variation during tissue culture was discovered. This line is also more freezing tolerant that Raleigh. Both genotypes are under field evaluation to observe other desirable characteristics before releasing them to growers.

Technical Abstract: The release of a freezing tolerant St Augustinegrass cultivar would greatly benefit home owners in many southern states because of the grass’s ability to tolerate shade and low moisture conditions. In an attempt to isolate genotypes more tolerant to freezing than the existing freezing-tolerant cultivar Raleigh, a two-pronged approach was employed. Germplasm was solicited in the areas near the north boundary of St Augustinegrass distribution, and tissue culture was utilized to induce somaclonal variations. Cold-acclimation increased freezing survival so a protocol was developed to apply acclimation under controlled conditions. Among the conditions tested, one week at 13°C followed by another week at 3°C, then freezing at –3 to -5°C, was optimal to distinguish genotypes in freezing tests. The experiments revealed that germplasm line Elm4 was significantly more freezing tolerant than Raleigh. In addition, out of 7800 regenerated plants through tissue culture, somaclonal variant SVC3 was significantly more tolerant to freezing than Raleigh.