WILT AVOIDANCE IN ST-AUGUSTINEGRASS GERMPLASM

St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is less dr ought-resistant than other C-4 grasses and frequently requires irrigat ion in lawns. The objectives of this study were to search for St. Augu stinegrass germplasm having little wilting and to determine if minimal wilting under drought is associated with reduced canopy loss. St. Aug ustinegrass cultivars and breeding lines, representing polyploids (2n = 27 to 32) and diploids (2n = 18), were grown in sand soil and expose d to irrigation suspensions during seasonal droughts in three experime nts. In the first experiment, during brief (3 to 14 day) irrigation su spensions, wilted area over 3 years was significantly less for polyplo ids (6% of canopy) than for diploids (23%). In the second experiment, during a permanent irrigation suspension, frequency of wilt was highes t for diploids (57%), least for African polyploids (27%), and intermed iate (53%) for other polyploids. When rain resumed after 41 days of dr ought, allowing refoliation, canopy loss was 51%, 4%, and 47% for dipl oids, African polyploids, and other polyploids, respectively. In the t hird experiment, during a permanent irrigation suspension, wilted area was 33% for 'Jade,' a diploid, which was more (P less than or equal t o 0.05) than for the polyploid 'FX-10,' with a wilted area of 20%. 'Fl oratam' and 'Bitterblue' were intermediate in wilted area, 28% and 25% , respectively. When rain resumed after 18 days of drought, canopy los s was 58% and 56% for 'Jade' and 'Bitterblue,' respectively, which was more than for 'Floratan' adn 'FX-10,' 11% and 6%. Following permanent irrigation suspensions, canopy loss was closely associated with wilti ng, r(2) = 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-avoida nt St. Augustinegrass may help reduce turfgrass water use.