Histological Analysis of Pre- and Post-Freezing Nodal Structure of St. Augustinegrass (Stenotaphrum secondatum (Walt.) Kuntze).

St. Augustinegrass has good shade tolerance, its relatively resistant to weed infestation, performs well under a wide range of soils, and has relatively low input requirements. All these characteristics make it a very desirable turfgrass for the Southeastern US. However, it is the least freezing-tolerant of the warm-season grasses and severe freezing injury may occur during some winters in USDA hardiness zones 8 and 9. Despite the identification of cold tolerant germplasm, limited progress has been made in breeding for cold tolerance in this species. A better understanding of the structure of St. Augustinegrass nodes and their relationship to freezing survival might aid in the development of better screening methods for freezing tolerance and ultimately improve selection efficiency of freeze-tolerant materials. This study was conducted to histologically analyze frozen and unfrozen nodes from cultivars ‘Raleigh’ and ‘Seville’. Histology results showed that node death is linked to plugged vessels after freezing. Moreover, plugged vessels and disrupted tissues occur at higher frequencies in the main stem than in new shoots. This would explain why re-growth was observed to begin in new shoots, which act independently from the main stem. Survival seems to be linked to reduction in water content and cell size as observed when comparing cross sections of main stems vs. new-shoot stems. Additionally, lignin content seems to play a role in freezing survival as regions of the node that stained a darker red had less structural damage. This is the first report on the nodal structure of St. Augustinegrass. Data generated from this study make a significant addition to the understanding of freezing survival in St. Augustinegrass.