Brian M. Schwartz

The genetic and phenotypic variability of interspecific hybrid bermudagrasses (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) used on golf course putting greens

AbstractMain conclusionSome interspecific hybrid bermudagrass cultivars used on golf course putting greens are genetically unstable, which has caused phenotypically different off-type grasses to occur in production nurseries and putting surfaces. Management practices to reduce the occurrence of off-type grasses in putting green surfaces and the effect they can have on putting quality and performance need to be researched until genetically stable cultivars are developed. Golf course putting green surfaces in subtropical and tropical climates are typically planted with an interspecific hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy), because of the superior putting quality and performance of these cultivars. ‘Tifgreen’ was one of the first interspecific hybrids developed for putting green use in lieu of common bermudagrass. However, off-type grasses began appearing in established Tifgreen stands soon after commercial release. Off-type grasses are those with different morphology and performance when compared to the surrounding, desirable cultivar. Off-types have the potential to decrease surface uniformity, which negatively affects putting surface quality. However, several unique off-types from Tifgreen have been selected as commercial cultivars, the first being ‘Tifdwarf’; then ‘Floradwarf’, ‘MS-Supreme’, ‘Pee Dee-102’, and ‘TL-2’, identified later. The cultivars ‘Champion Dwarf’, ‘P-18’, ‘RJT’, and ‘Emerald Dwarf’ were subsequently selected as off-types in Tifdwarf. The naturally occurring off-types and cultivars that have been identified within the Tifgreen family have widely differing phenotypes; however, they are reported to be genetically similar, supporting the hypothesis that their occurrence is a result of somatic mutations. Genetic instability in currently available commercial cultivars is likely to lead to the continued presence of off-types in production nurseries and putting greens. Additional research is needed to understand the nature of genetic instability in Tifgreen-derived cultivars and how to manage its consequences to develop new cultivars, but also strategies for eradication of off-types in pedigree nursery production and end-site putting greens.

Cross-taxon application of sugarcane EST-SSR to genetic diversity analysis of bermudagrass (Cynodon spp.)

Bermudagrass lags in genomic and molecular breeding resources, particularly regarding a critical mass of robust, reproducible, and highly polymorphic molecular markers like simple sequence repeats (SSR). Here, 2017 sugarcane EST-SSR primer pairs (PPs) were screened for transferability and polymorphisms against commercial triploid hybrids and representatives of their parental species, tetraploid Cynodon dactylon and diploid C. transvaalensis. Fifty-four percent of PPs amplified target SSR in at least one of the two species, while 62% of these ‘transferable’ SSR were polymorphic. A subset of 228 polymorphic markers was utilized for genotyping 24 samples that included: 10 ‘Tif’ series cultivars (i.e., released from Tifton, GA), their parental species, 10 F1 hybrids between the two species, and two diverse Sorghum spp. A total of 90 and 144 PPs produced reproducible bands in the bermudagrass samples and the sorghum species, respectively. While 63 (70%) PPs were polymorphic among members of the ‘Tif’ diversity panel, 79 (54.8%) were polymorphic between the sorghum species. Further, 57 PPs polymorphic in the ‘Tif’ diversity panel were genotyped against 3 experimental lines and 7 commercial hybrids including ‘TifTuf’, a recent addition to the ‘Tif’ series. Joint analysis of 24 genotypes grouped bermudagrass accessions into two main clusters, one including C. dactylon and the other including C. transvaalensis. A small set of informative SSR readily differentiated the cultivar groups and identified potentially mischaracterized cultivars, but did not differentiate among mutants within cultivar groups. Heterologous EST-SSR from sugarcane are useful sources of polymorphic markers for cultivar identification in bermudagrass, and build on existing marker resources to facilitate genetic mapping, QTL analysis, and marker assisted selection.

Preemergence Herbicides Influence Sprig Establishment of ‘TifEagle’ Bermudagrass

Abstract The presence of weeds during bermudagrass putting green establishment can reduce growth and turf quality. Three field experiments were conducted in Georgia to investigate efficacy of dimethenamid, S-metolachlor, and oxadiazon on the establishment of ‘TifEagle’ bermudagrass from sprigs. Dimethenamid at 0.85 and 1.7 kg ai ha−1, S-metolachlor at 1.1 and 2.2 kg ai ha−1, and oxadiazon at 1.1, 2.2, and 4.4 kg ai ha−1 did not reduce bermudagrass cover from the untreated after 8 wk. S-metolachlor at 4.4 kg ha−1 was the only treatment that reduced sprig cover from the untreated after 12 wk. All S-metolachlor and oxadiazon treatments provided excellent (≥ 90%) green kyllinga control by 8 wk after treatment (WAT) while dimethenamid at 0.85, 1.7, and 3.4 kg ha−1 provided 78, 85, and 92% control, respectively. Dimethenamid treatments provided poor control (< 70%) of spotted spurge but fair control (70 to 79%) was achieved from S-metolachlor at 4.4 kg ha−1 and oxadiazon at 2.2 and 4.4 kg ha−1 by 8 WAT. Overall, low to middle rates of the herbicides tested appear to temporarily inhibit TifEagle bermudagrass sprig establishment but high rates of dimethenamid and S-metolachlor may reduce cover from the untreated. Nomenclature: Hybrid bermudagrass, Cynodon dactylon × C. transvaalensis Burtt-Davy; green kyllinga, Kyllinga brevifolia Rottb.; spotted spurge, Euphorbia maculata L.

Genotypic and phenotypic evaluation of off-type grasses in hybrid Bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] putting greens using genotyping-by-sequencing and morphological characterization

BackgroundInterspecific hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] is one of the most widely used grasses on golf courses, with cultivars derived from ‘Tifgreen’ or ‘Tifdwarf’ particularly used for putting greens. Many bermudagrass cultivars established for putting greens can be genetically unstable and lead to the occurrence of undesirable off-type grasses that vary in phenotype. The objective of this research was to genetically and phenotypically differentiate off-type grasses and hybrid cultivars. Beginning in 2013, off-type and desirable hybrid bermudagrass samples were collected from golf course putting greens in the southeastern United States and genetically and phenotypically characterized using genotyping-by-sequencing and morphology.ResultsGenotyping-by-sequencing determined that 11% (5) of off-type and desirable samples from putting greens were genetically divergent from standard cultivars such as Champion, MiniVerde, Tifdwarf, TifEagle, and Tifgreen. In addition, genotyping-by-sequencing was unable to genetically distinguish all standard cultivars from one another due to their similar origin and clonal propagation; however, over 90,000 potentially informative nucleotide variants were identified among the triploid hybrid cultivars.ConclusionsAlthough few genetic differences were found in this research, samples harvested from golf course putting greens had variable morphology and were clustered into three distinct phenotypic groups. The majority of off-type grasses in hybrid bermudagrass putting greens were genetically similar with variable morphological traits. Off-type grasses within golf course putting greens have the potential to compromise putting surface functionality and aesthetics.

Evaluating Hybrid Bermudagrass Using Spectral Reflectance under Different Mowing Heights and Trinexapac-ethyl Applications

Quantitative spectral reflectance data have the potential to improve the evaluation of turfgrasses in variety trials when management practices are factors in the testing of turf aesthetics and functionality. However, the practical application of this methodology has not been well developed. The objectives of this research were 1) to establish a relationship between spectral reflectance and turfgrass quality (TQ) and percent green cover (PGC) using selected reference plots; 2) to compare aesthetic performance (TQ, PGC, and vegetation indices) and functional performance (surface firmness); and 3) to evaluate lignin content as an alternate means to predict surface firmness in turfgrass variety trials of hybrid bermudagrass [Cynodon dactylon ·C. transvaalensis]. A field study was conducted on mature stands of three varieties (‘TifTuf’, ‘TifSport’, and ‘Tifway’) and two experimental lines (04-47 and 04-76) at two mowing heights (0.5 and 1.5 inch) and trinexapac-ethyl application (0.15 kg ha and nontreated control) treatments. Aesthetic performance was estimated by vegetation indices, spectral reflectance, visual TQ, and PGC. The functional performance of each variety/line was measured through surface firmness and fiber analysis. Regression analyses were similar when using only reference plots or all the plots to determine the relationship between individual aesthetic characteristics. Experimental line 04-47 had lower density in Apr. 2010, whereas varieties ‘TifTuf’, ‘TifSport’, and ‘Tifway’ were in the top statistical group for aesthetic performance when differences were found. ‘TifSport’ and ‘Tifway’ produced the firmest surfaces, followed by ‘TifTuf’, and finally 04-76 and 04-47,which provided the least firm surface. Results of leaf fiber analysis were not correlated with turf surface firmness. This study indicates that incorporating quantitative measures of spectral reflectance could reduce time and improve precision of data collection as long as reference plots with adequate range of green cover are present in the trials.

Evaluation of Chinese Centipedegrasses and other Turfgrass Taxa for Potential Resistance to Twolined Spittlebug, Prosapia bicincta (Say)

Abstract Warm season turf taxa of centipedegrass [Eremochloa ophiuroides (Munro) Hack], bermudagrass [Cynodon L.C. Rich, spp.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and zoysiagrass [Zoysia Willd. spp.] were evaluated for tolerance to adult twolined spittlebug (Prosapia bicincta Say) feeding in choice and no-choice experiments, and for their ability to support nymphal development (antibiosis potential). Among 133 selections evaluated, few showed evidence of potential antibiosis and/or improved tolerance over commercially available cultivars. Most of the centipedegrass taxa evaluated were susceptible to the spittlebug. However, some potential antibiosis among Chinese centipedegrass taxa was identified, and there was a gradient in the ability to tolerate spittlebug feeding. Among centipedegrasses, TC 358 and TC 362 showed moderate tolerance and recovery in no-choice and choice trials. The most tolerant bermudagrasses in no-choice trials were 00 - 23, 03 - 14, and 03 - 15. Centipedegrasses overall were the best hosts for nymph development, but TC 379, TC 422 and E. ciliaris did not support nymph development, and TC 341 and TC 399 showed very low numbers of nymphs. The bermudagrasses 00 - 23 and 00 - 28 and the St. Augustinegrasses T638 and Mercedes failed to support nymph development.