Abstract

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is less drought resistant than other C₄ grasses and frequently requires irrigation in lawns.  The objectives of this study were to search for St. Augustinegrass germplasm having little wilting and to determine if minimal wilting under drought is associated with reduced canopy loss.  St. Augustinegrass cultivars and breeding lines, representing polyploids (2n = 27 to 32) and diploids (2n = 18), were grown in sand soil and exposed to irrigation suspensions during seasonal droughts in three experiments.   In the first experiment, during brief (3 to 14 day) irrigation suspensions, wilted area over 3 years was significantly less for polyploids (6% of canopy) than diploids (23%).  In the second experiment, during a permanent irrigation suspension, frequency of wilt was highest for diploids (57%), least for African polyploids (27%), and intermediate (53%) for other polyploids.  When rain resumed after 41 days of drought, allowing refoliation, canopy loss was 51%, 4%, and 47% for diploids, African polyploids, and other polyploids, respectively.  In the third experiment, during a permanent irrigation suspension, wilted area was 33% for 'Jade,' a diploid, which was more (P < 0.05) than for the polyploid 'FX-10,' with a wilted area of 20%.  'Floratam' and 'Bitterblue' were intermediate in wilted area, 28% and 25%, respectively.  When rain resumed after 18 days of drought, canopy loss was 58% and 56% for 'Jade' and 'Bitterblue,' respectively, which were more than for 'Floratam' and 'FX-10,' 11% and 6%.  Following permanent irrigation suspensions, canopy loss was closely associated with wilting, r² = 0.88 and 0.94 by the Gompertz nonlinear model.  Because the sand soil had low water-holding capacity, the wet subsoil and shallow (1.35-m deep) water table may have been a source of water.  Wilt-avoidant St. Augustinegrass may help reduce turfgrass water use.