Comparing Water Requirements of Diploid and Interploid St. Augustinegrass.

Compared to diploid St. Augustinegrasses (Stenotaphrum secundatum Walt. Kuntze) polyploids are more resistant to biotic and abiotic stresses such as drought. The development of interploid hybrids between diploid and polyploid St. Augustinegrass using embryo rescue offers to improve drought tolerance while maintaining visual quality. This study is aimed to compare the water requirements of seven diploid and nineteen interploid hybrids to four commercial checks, namely, Palmetto and Raleigh (diploids), TamStar (interploid), and Floratam (anueploid) under short-term drought conditions. The study was planted as a randomized complete block with three replications on 22 Aug. 2014. Dry-down was initiated on 30 June 2015 under a rainout shelter for 86 days in year 1 and on 6 July 2016 in year 2. Digital image analysis was used to determine average green cover (%) weekly beginning 16 July 2015 in year 1 and 13 July 2016 in year 2. Entries with green cover ≤ 50 ± 1 % were supplied with 2.54 cm of water. Quality was rated from 1 to 9 (1 = poor; 9 = excellent; 5 = minimum acceptable). The mean green cover and quality in year 1 were highest for interploids (77.4%, 5.2), followed by Floratam (65.7%, 4.4), and then diploids (64.3%, 4.1). Two diploids required water after 51 d of dry-down. Two interploids and Floratam were watered at 72 d, and the remaining eighteen interploids, including TamStar, did not require water. In total, six diploids, including Palmetto and Raleigh, received between 5.08 cm and 12.7 cm of water, whereas Floratam and two interploids received 5.08 cm and 2.54 cm, respectively. Green cover (50%) was correlated to an average quality rating of 3.6 (R² = 0.81), but to retain acceptable quality (5.0) the suggested percent green cover was 76.2%. Preliminary results suggest interploid St. Augustinegrasses outperform Floratam and diploids for drought tolerance. Additionally, a higher threshold of at least 75% green cover may need to be considered for future drought studies in St. Augustinegrass. Data for year 2 will also be presented.