Genotype and Sting Nematode Effects On Root Parameters of St. Augustinegrass.

Sting nematodes can be significant pests of St. Augustinegrasses on light textured soils in the southeastern USA.  We investigated the effects of three levels of sting nematode infestation (0, 50, and 300 nematodes added per 600 cm³ cylindrical tube) and three cultivars of St. Augustinegrass (‘Captiva’, ‘Floratam’ and ‘Palmetto’) on various root parameters.  Two three node cuttings were initially inserted into tubes filled with medium grade greens sand and allowed to root for three weeks under mist irrigation.  After rooting, sting nematodes were added in a water solution to two holes made ca. 5 cm deep in the surface of the sand in each tube.  Plants were then grown for 90 days in a greenhouse.  The plants were fertilized prior to inoculation with nematodes and at 30 and 60 days with a rate 30 mg N per cone from a soluble 20-20-20 (N-P₂O₅-K₂O) fertilizer.  The experiment was terminated by removing the soil-root mass from the tubes, extracting the nematodes from the soil using a sucrose flotation method, and then washing the roots free of the sand.  Nematodes were counted in the University of Florida Landscape Nematology Laboratory, and roots were scanned using Root-Rhizo scanning software on roots floated in a water Plexiglas tray.  Cultivars did not differ in numbers of sting nematodes per tube.  Numbers of nematodes increased to ca. 100 in the 50 inoculation level tubes and decreased to ca. 170 in the 300 inoculation level tubes. Root diameters and volume were higher for Floratam, intermediate for Palmetto, and lowest for Captiva.  Root dry weights generally were highest at the 0 nematode level, intermediate at the 50 level and lowest at the 300 nematode level.