Since its release in 1951, Meyer zoysiagrass (Zoysia japonica) remains one of the most winter-hardy zoysiagrass cultivars, which is also why it is still the most widely used zoysiagrass cultivar on golf courses in the transition zone today (6, 10, 11).
Research-proven differences in winter hardiness among cultivars of zoysiagrass is one of the main reasons zoysiagrass cultivar selections vary by geographic location (9, 10). In the last two decades, breeding programs have made progress in the development
of zoysiagrass hybrids with comparable winter hardiness to Meyer, but with superior establishment rate, turf quality, shade tolerance, leaf texture or pest tolerance compared to Meyer. Some examples include Chisholm zoysiagrass (3, 8), Innovation
zoysiagrass (4) and Lobo zoysiagrass (1). However, breeding efforts continue because there are still many improved traits yet to be desired, such as improved disease tolerance.
Figure 1. The multiple phases of developing large patch-tolerant and winter-hardy zoysiagrass cultivars for the transition zone led by Texas A&M AgriLife Research, Texas A&M University in Dallas.
One of the advantages of zoysiagrass compared to other turfgrass species is the few diseases it encounters (11). The fungal disease Rhizoctonia large patch caused by Rhizoctonia solani Kühn (AG 2-2 LP) affects zoysiagrass, especially Meyer, throughout
the transition zone and can be extremely damaging (7). Large patch, which occurs in spring and autumn and typically leads to thinning of the turf and potential weed encroachment, is a limitation to increasing the use of zoysiagrass on U.S. golf courses (11), and fungicide costs associated to prevent/control this disease can be a large portion of a zoysiagrass golf course’s budget (5). Therefore, breeding for improved large patch tolerance (LPT) in new zoysiagrass cultivars to overcome this problem can help reduce fungicide requirements and increase sustainability for golf course superintendents.
Recently, a collaborative effort among three universities (Texas A&M AgriLife Research, Kansas State University and Purdue University), led by scientists at Texas A&M AgriLife Research, Texas A&M University in Dallas, developed experimental zoysiagrass hybrids with demonstrated improvements in turf quality, winter hardiness and tolerance to large patch in comparison to Meyer in the field (2). The research presented in this article was conducted over a 10-year period using a systematic multiple-phase approach with the objective to develop and thoroughly assess improved turf performance, LPT and winter hardiness of new, fine-textured zoysiagrasses for the transition zone (2) (Figure 1).
Figure 2. Zoysiagrass plots in West Lafayette, Ind., which was one of 10 replicated field sites to evaluate turfgrass performance and stress tolerance for multiple years in Phase 3. Photo by Aaron Patton
In Phase 1, the team led by Ambika Chandra, Ph.D., in Dallas crossed elite experimental zoysiagrass hybrids with germplasm accessions that were finer textured (i.e., narrower leaves) and demonstrated some LPT with winter-hardy zoysiagrass parental lines
(Meyer and Meyer derivatives) to produce 2,858 new interspecific hybrids of zoysiagrass between 2011 to 2012. In Phase 2 (2012-2014), these 2,858 zoysiagrass progeny were sent out to be evaluated for two years as spaced-plant nurseries across three
sites (Dallas; West Lafayette, Ind.; and Manhattan, Kan.). In addition to the progeny, one or more replications of commercially available cultivar checks of zoysiagrass, such as Meyer, Zorro, Chinese Common, Cavalier, Zeon, Chisholm, Cashmere, Zenith
and Diamond, were planted at each site for standard comparison. After two years of data collection, researchers at each site selected the 20 best entries (60 total, 2% of 2,858 progeny) that were consistently in the highest rankings for their site
to move on to Phase 3 for further evaluation in replicated field trials.
Table 1. Replicated field trials locations and cooperators in Phase 3 from 2015–2017. a: Average annual minimum winter temperature in parentheses; USDA map retrieved from https://planthardiness.ars.usda.gov. b: Ancillary locations for large patch incidence.
The objective of Phase 3 (2015-2017) was to select the top 10 of 60 experimental hybrids that have comparable or superior winter hardiness to Meyer, but with finer leaf texture, improved turf performance and LPT across replicated multiyear field trials of 10 sites (Table 1; Figure 2). There was a wide range of variability in turf characteristics, including turf quality, turf cover and winterkill within and across sites. The top 10 DALZ hybrids selected from Phase 3 had turf cover exceeding that of Meyer across all sites. Most of the entries displayed lower large patch incidence compared to cultivar checks, especially Meyer, in Arkansas in April and May in 2017, and in Kansas in October and November in 2016, indicating increased tolerance (Table 2). Overall, among the group of 60 experimental hybrids in Phase 3, there were promising progeny that consistently exhibited good winter hardiness, LPT and improved turf quality characteristics compared to cultivar checks across all locations in the transition zone, indicated by their turf performance index scores, which is the number of times a treatment occurred in the top statistical group across all parameters (a higher number is desirable). After Phase 3, the top 10 promising progeny (assigned DALZ numbers) required further intensive field and laboratory testing in Phase 4.
Table 2. Turf performance index (based on three-year observation ratings from 10 locations) and large patch infection (observed in Arkansas and Kansas) of the 10 zoysiagrass progeny (bolded) selected for further research compared to cultivars checks.
a: TPI is the turf performance index representing the number of times an entry occurred in the top statistical group (a higher number is desirable). It is based across the 10 sites (Arkansas, Illinois, Indiana, Kansas, Missouri, North Carolina, Oklahoma, Tennessee, Texas, Virginia).
b: Large patch was rated visually on a 0% to 100% scale on the entire plot in Arkansas and on the R. solani-inoculated half of each plot in Kansas.
c: 2016 TPI is based upon one winterkill rating in Indiana; spring green-up ratings at six sites; large patch tolerance in two months at Kansas; percent turf cover at eight sites; fall color ratings at six sites; genetic color ratings at six sites; leaf texture ratings at six sites; and turf quality ratings in seven months (Missouri), six months (Arkansas, Oklahoma, Texas), four months (North Carolina), three months (Indiana), two months (Kansas, Virginia), and one month (Illinois) (max 72).
d: 2017 TPI is based upon winterkill ratings at five sites; spring green-up ratings at six sites; large patch tolerance in two months (Arkansas) and four months (Kansas); fall color ratings at seven sites; genetic color ratings at six sites; leaf texture ratings at eight sites; and turf quality ratings in seven months (Kansas, Oklahoma), six months (North Carolina, Texas), five months (Indiana, Missouri), three months (Arkansas), and one month (Illinois) (max 78).
e: Texas Agricultural Experiment Station (TAES) entry code.
f: LSD, least significant difference between large patch cover (0%–100%) means within a column at P = 0.05.
The objective of Phase 4 (2018-2022) was to evaluate the top 10 elite experimental zoysiagrass hybrids selected from Phase 3 compared to commercially available zoysiagrass cultivars, including recently released Innovation, at five golf courses and three research farm environments in the transition zone (Figure 3). Additional objectives included freeze tolerance testing, leaf width measurements, drought resistance, golf ball lie performance, dark green color index (DGCI) and other intensive measurements
(Figures 4 and 5). Phase 4 revealed differences in establishment rate among genotypes, with DALZ 1703, 1808, 1811 and 1812 often exhibiting faster turf establishment across multiple sites compared to the other genotypes and cultivar checks. Overall, the majority of these DALZ genotypes exhibited a faster or similar establishment compared to Innovation or Meyer. Turf performance index scores from Phase 4 indicated DALZ 1701, 1702, 1707 and 1810 had moderate-to-good turf performance across seven
sites, while DALZ 1808 had similar or slightly lower performance (Figure 6). Meyer consistently performed poorly, and Innovation had poor-to-moderate performance in comparison to the experimental genotypes, which highlights the improvements achieved in zoysiagrass breeding in the last 10 years through this process.
Figure 3. Zoysiagrass plots in West Lafayette, Ind., during Phase 4, which consisted of additional field evaluations for turfgrass
performance, golf ball lie percentage, billbug resistance, dark green color index and more. Photo by Aaron Patton
A finer leaf texture (i.e., smaller leaf width) was measured in all DALZ genotypes compared to Meyer. Freeze tolerance (LT50, lethal temperature killing 50% of the plants) ranged from 14.4 F (-9.8 C) (Diamond Z. matrella) to 6.6 F (-14.1 C) (DALZ 1812) with a mean of 9.5 F (-12.5 C). All DALZ genotypes with Z. japonica lineage exhibited similar freeze tolerance to Meyer, which illustrates similar winter hardiness and potential for use in northern transition climates. Evidence of large patch in the top 10 DALZ genotypes was 15% to 40% lower than Meyer on several dates, which indicates potential opportunities for reduced fungicide use. Overall, results from this 10-year systematic breeding process indicate there are multiple genotypes for potential zoysiagrass release in the future that will have improved turf performance, drought tolerance, large patch tolerance, darker green turf color, finer leaf texture and good winter hardiness and freeze tolerance for a variety of climates across northern and southern areas of the transition zone.
Figure 4. Example of an image of a golf ball lie in zoysiagrass that measures the percentage of the golf ball exposed
above the turf canopy utilizing image analysis software. Photo by Ross Braun
DALZ 1701 is one of these top-performing DALZ genotypes that is planned to be released in 2023. Some characteristics of DALZ 1701 are: 1) similar freezing tolerance compared to Meyer; 2) superior heat tolerance than Meyer, Emerald and Zeon zoysiagrass; 3) improved drought tolerance compared to Meyer and similar to Empire; 4) darker green genetic color and improved fall color retention compared to Meyer; 5) superior tolerance to take-all patch, mites and hunting billbug compared to Meyer; and 6) acceptable turf performance across USDA plant hardiness zones 5b to 8a (Chandra et al., 2023). DALZ 1701 is adapted to multiple environments across the northern, transition and southern regions of the United States where zoysiagrass is grown and is suitable for home lawns, golf course fairways and tees.
Figure 5. Freeze tolerance survival of zoysiagrasses in Phase 4 in West Lafayette, Ind., during Phase 4 of a 10-year, four-phase collaborative effort among three universities to develop new hybrid zoysiagrasses. Zoysiagrass plugs in conetainers were subjected to freezing temperatures from check (nonfreezing) (far right side, 19.4 F (−7 C) (right side) to 3.2 F (−16 C) (far left side). Photo by Ross Braun
The authors wish to acknowledge the funding support by the United States Golf Association, USGA ID# 2012-24-458. We also thank collaborators listed in Table 1 for their efforts in Phase 3 of this research. In addition, we thank Mingying Xiang, Ph.D.;
Manoj Chhetri, Ph.D.; Dani McFadden; Pawel Petelewicz, Ph.D.; and other personnel at the research centers for their efforts in this research; and Scott Johnson, Brad Pugh, Randy Brehmer, Thomas Slevin, Sean Tully and Doug Wiggers for hosting and managing
a zoysiagrass expansion site at their golf course in Phase 4. The full manuscript on this experiment is available in Crop Science (https://doi.org/10.1002/csc2.20834).
Figure 6. Cumulative turf performance index score at each location, which is the number of times a treatment occurred in the top statistical group across all parameters except establishment rate. Across all sites, treatments are sorted numerically by DALZ code with the two cultivar checks at the bottom. The site code abbreviation and maximum possible turf performance index number are the following: Shadow Glen Golf Club, Olathe, Kan. (KS1, 13); Rocky Ford Turfgrass Research Center, Manhattan, Kan. (KS2, 32); The Fort Golf Course, Indianapolis (IN1, 15); The Country Club of Terre Haute, Terre Haute, Ind. (IN2, 8); W.H. Daniel Turfgrass Research and Diagnostic Center, West Lafayette, Ind. (IN3, 29); Napa Golf Course, Napa, Calif. (CA, 26); and Texas A&M AgriLife Research and Extension Center, Dallas, (TX, 31). The blank cell with “×” indicates Meyer was not planted at the location.
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Ross C. Braun (email@example.com) is an assistant professor and director of Rocky Ford Turfgrass Research Center in the Department of Horticulture and Natural Resources, Kansas State University, Manhattan; Ambika Chandra is a professor in the Department of Soil and Crop Sciences, Texas A&M AgriLife Research, Dallas; Aaron J. Patton is a professor in the Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Ind.; and Jack D. Fry is a professor of research and Extension specialist for Commercial Turf at Kansas State University, Manhattan.