Evaluation of Off-Type Grasses in Interspecific Hybrid Bermudagrass [<i>Cynodon dactylon</i> (L.) Pers. x <i>C. transvaalensis</i> Burtt-Davy] Putting Greens

The economic impact of the golf industry in the United States (U.S.) in 2011 was estimated to be $176.8 billion. Interspecific hybrid bermudagrasses [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] are some of the most widely utilized grasses on golf courses throughout tropical, subtropical, and temperate climates. In 2007, bermudagrass was grown on 80% of putting green acreage in the southern U.S. ‘Tifgreen’ and ‘Tifdwarf’ were two of the first widely established cultivars on putting greens, but their genetic instability led to the occurrence of phenotypically different off-type (OT) grasses. Several OT grasses were selected and released as cultivars such as ‘Champion’, ‘MiniVerde’, and ‘TifEagle’. These cultivars can also be genetically unstable and OT grasses can occur in putting greens. The objectives of this research were to genetically and phenotypically characterize OT grasses and evaluate their responses to nitrogen (N) and trinexapac-ethyl (TE) applications. Off-type and desirable bermudagrass samples were collected from Champion, MiniVerde, and TifEagle golf course putting greens in 2013 and 2014. Grasses were genetically evaluated using genotyping-by-sequencing (GBS), which determined that 11% were genetically divergent from standard cultivars. Off-types were phenotypically characterized using morphology and samples clustered into three distinct morphological groups that varied in internode length and leaf length. The response of OT grasses and cultivars to six N and eight TE treatments was evaluated by measuring clippings 7, 14, 21, and 28 days after initial treatment (DAIT). The least three N rates decreased weekly clipping production 18 to 29% [percent], whereas the greatest three rates sustained growth. We observed that peak growth regulation occurred 21 DAIT for the majority of TE rates tested where clipping weights decreased 18 to 35% from 7 to 21 DAIT. We also observed a period of increased clipping production 18 to 47% from 21 to 28 DAIT for all grasses tested. It is important to maintain consistent growth among phenotypically different grasses in order to minimize any competitive growth advantage an OT grass may possess over a desirable cultivar in a golf course putting green.