Off-types in bermudagrass—genetically distinct patches differing in color, height, or texture—disrupt turf uniformity and performance on golf courses and sports fields. While sometimes called “mutations,” most off-types I’ve observed in 49 years of Florida turfgrass research are likely contaminations from other cultivars or wild bermudagrass—not true genetic mutations.
Scope
Most of the following is on turfgrass cultivars of bermudagrass (Cynodon species) used on golf course fairways and tees, and sports fields, not on greens.
The mutational hypothesis of origin of off-types in greens bermudagrasses such as ‘Tifgreen,’ ‘Tifdwarf,’ and related cultivars, is mentioned but not fully addressed because research is incomplete. Briefly, greens grasses such as Tifgreen, Tifdwarf, and ultradwarf cultivars (e.g., TifEagle, Miniverde, and Champion) have appreciable genetic instability. Mutation-like events may explain the initial appearance of off-types in greens bermudagrasses, which then expand and are replanted mechanically, becoming contaminants.
Bermudagrass species and complex genetics
Bermudagrass, the genus Cynodon, has a long and complex history. It includes about 8 to 10 species such as Cynodon dactylon (common bermudagrass), C. transvaalensis (African bermudagrass), along with their interspecific hybrids such as C. x magennisii (hybrid bermudagrass). Because of its worldwide importance as a turfgrass, forage, and weed, there is a vast and growing scientific literature on bermudagrass and the genetics of off-types. At this point, despite many published studies, the origin of greens off-types is mutation-like but their genetic nature is still not understood.
To understand off-types, we must first understand vegetative propagation.
Vegetative propagation and genetic uniformity
Most improved bermudagrass cultivars like Bimini, Celebration, Tifdwarf, TifTuf, and Tifway are vegetatively propagated—grown from stem cuttings of a single parent sprig selected by a turfgrass breeder. Every cell in every stolon and leaf blade is genetically identical. This uniformity results from asexual (mitotic) cell division, thus clonal descent from the original sprig.
This method helps ensure consistency in appearance and play. However, when contamination occurs during production, handling, or planting, that uniformity is disrupted. Off-types are highly noticeable due to differences in color, height, or texture.
Certification protecting the chain of custody
To prevent contamination, maintaining a strict chain of custody is essential. At each stage of propagation, plant material must be:
- documented as to where it came from, and
- isolated from other cultivars and potential off-types.
Across the U.S., this process is supported by AOSCA (the Association of Official Seed Certifying Agencies), which uses a four-tiered certification system. The tiers are Breeder, Foundation, Registered, and Certified Seed Classes. “Seed” in this context refers to vegetative cuttings, not seeds produced through sexual reproduction.
The Southern Seed Certification Association (SSCA), an AOSCA member and non-profit corporation, was authorized by the Florida Commissioner of Agriculture with responsibility for seed certification in Florida, beginning in 1996. The responsibility was then governed by Florida Seed Law, Statutes Chapter 575.02, with a purpose “. . . to make available to the public high quality seed of superior crop plant varieties so grown and distributed as to insure genetic identity and genetic purity.” The current statute definitions, Chapter 578.011, uses the expression, “genetic purity and identity.” The SSCA does not represent growers or consumers but acts as an independent, neutral third party.
Documentation
For certification to work, all stages and transfers must be diligently recorded: letters, release descriptions, signed inspection reports, and formal agreements are required. Sod farmers must apply for certification in conjunction with fumigating fields and sourcing planting material from other certified producers. A well-organized, trackable system allows for a clear pedigree of propagation. Ideally, this traces all the way back to the original sprig from the turfgrass breeder. This process ensures that the grass is delivered true-to-type to the golf course or sports field.
Field inspection procedures
As part of upholding certification standards, I inspected more than 200 Florida sod fields for SSCA over seven years—about 2000 acres inspected three times per year, totaling over 2 billion square feet. The vast majority of acreage in the program in Florida was bermudgrass cultivars for golf course fairways and sports turf fields.
Using wire flags, I marked and recorded over 55,000 vegetation contamination points that had invasive perennial plants, almost always grasses, that required killing using a nonselective herbicide applied as a spot treatment by sod farm staff. Each flag was accompanied by one geospatial waypoint that I recorded with a handheld GPS device. Each point was an area not more than 3 feet in diameter. Larger contamination spots received more than one flag and waypoint. The vast majority of spots were bermudagrass off-types. These included common bermudagrass, other cultivars of bermudagrass, and unidentified genotypes.
Visual accuracy in the field and transplant validation
To avoid misidentification (false negatives and false positives), the procedure that I established required at least three visible differences—such as color, height, width, seediness, or stolon orientation—for field determination of an off-type. Ideally, the off-type spot’s boundary also was sharply defined within the matrix of the dominant cultivar.
Some spots were other turf species and noxious weeds. My reports and maps of waypoints that I mailed to sod growers showed where off-types were present. Spots were generally clustered, not randomly distributed, and often along the edges and corners of fields and near truck access points. But many fields had off-type concentrations in the interiors. The tendency for off-types to occur in geospatial clusters is consistent with contamination spread, not spontaneous mutation.
To validate off-types as genetic variants, I created a potted transplant garden of sprigs from contaminant spots that I had collected from sod farms. This way I could compare off-types with samples of known cultivars in a common environment. This was helpful to control for environmental effects and for making careful measurements.
Environment effects
Bermudagrass has strong phenotypic plasticity in response to field environmental conditions. For example, color differences may reflect moisture variations caused by topography and distances from field ditches. Biotic factors were also observed and taken notice of, such as nutrient enrichment due to deer droppings or fire ant activity, and localized damage from the bermudagrass stunt mite.
These most obvious environmental factors affecting plant appearance were discerned in the field, lessening the risk of marking false positives. So the off-type transplant garden was thus a backup and reference for measurements, not a primary method of off-type recognition.
Cytogenetics of an off-type
Within 3 weeks, bermudagrass transplants produced new growth responsive to the transplant environment. True genotypic differences became more strongly visible in the new growth.
I rarely got pushback from growers about my removing their fields from certification. Most welcomed the opportunity to protect themselves and their customers. But when I did get pushback, having a transplant nursery gave me backup assurance that my field eyes were not lying.
Working with Kevin Kenworthy, Ken Quesenberry, and Jamie Buhlman, we performed flow cytometry to characterize a Lanky Yellow-green (LYG) off-type that occurred frequently in Celebration bermudagrass. Based on carefully prepared pairs of LYG bermudagrass vs. Celebration bermudagrass, we determined that the LYG off-type was in 8 out of 11 instances a chromosomal variant with 2n=27 chromosomes, compared with Celebration which had 2n=36 chromosomes. Whatever its origin, the LYG off-type in Celebration was a widespread contaminant.
How off-types were distributed and spread across farms
No turfgrass producer was immune from off-types. By the end of the first year of inspection, I had rejected 46% of the Tifway acreage that had been applied for. Even previously clean fields developed off-types over time and had to be rejected. A single inspection wasn’t always conclusive due to lighting or weather, but I always documented decisions thoroughly—so growers could take corrective action and request reinspection.
Off-type frequency was reduced over seven years of inspection. There might have been a trend, that was not analyzed, in off-type frequency being positively related to the total age of fields at the time of inspection. But summarizing trends across reports would risk obscuring key case-specific details—such as planting sources, field history before fumigation, type of fumigant used, and failures of fumigation.
Some off-types found in Certified fields traced back to Registered fields, sometimes from different producers. In one case, a previously clean Foundation field developed contamination and had to be rejected. Since bermudagrass spreads quickly, small contaminations can expand and create widespread off-type outbreaks.
Off-types reappear as survivors from renovation
I’ve also observed off-types in golf courses that had been replanted with supposedly clean turf. In most cases, the off-types likely originated as regrowth from earlier planted cultivars that were not fully eradicated from the golf course before replanting. These contaminants can lie dormant underground and reappear later.
Methyl bromide is the most effective fumigant. However, it is no longer available for golf course use. The one fumigant labeled for golf course renovation was, at the time of this writing, basamidT (active ingredient Dazomet). It is very expensive. Nonselective herbicides like glyphosate require months of repeat applications to be marginally effective. Tight renovation timelines make full eradication extremely difficult.
A case of renovation survival on a sod farm
In one case, a sod farm, in which methyl bromide was used to eliminate Latitude 36 bermudagrass, and which was replanted with Celebration, Latitude 36 reemerged in a major breakout.
All of the off-types were phenotypically identical to the original Latitude 36 grass. So, even fumigation may fail. In subsequent interview of the grower, I learned that plastic tarps had indeed been torn by wind soon after the fumigation.
Off-types may arise through on-site mutation
The third possible source of off-types is sudden mutational change in DNA caused by radiation or replication errors. Most mutations are harmful (so they don’t usually prevail) and are random in effect.
In separate gamma-ray research with St. Augustinegrass, I observed a vast array of unique mutations—no two were the same. In contrast, off-types in bermudagrass fields often appeared in repetitions of the same characteristics, pointing to off-type contamination, not mutation.
While some greens cultivars like Tifgreen and Tifdwarf are considered genetically unstable, their off-types often cannot be distinguished genetically. Still, they are phenotypically different, and once present, may be propagated and spread.
Tifway, by contrast, is genetically stable but frequently contaminated by recognizable variants such as “Yellow dog,” Ormond, and common bermudagrass.
Off-types may arise as seed through sexual reproduction
A fourth possible source of variation in bermudagrass is viable seeds produced through sexual reproduction involving pollination. Cultivar descriptions and patents of bermudagrass often do not say whether viable seed is or is not produced. Vegetatively propagated turfgrasses are generally considered sterile when it comes to sexual reproduction. This is partly because most are triploids with 2n = 27 chromosomes.
Odd-numbered chromosomes do not pair nicely in meiosis and when the daughter cells try to separate it is a biological mess. Vegetatively propagated tetraploid cultivars, with 2n=36 chromosomes, which are few, are potentially more likely to reproduce sexually and produce seeds from inflorescences. They include Celebration, MS-Choice, Premiere, and Vamont. But chromosome number is predictive of seed fertility, not determinative.
Mutation often blamed, but contamination likelier
In a notable case, three golf courses planted with Tifway (T-119) from the same sod farm all showed the same blue-green Ormond-like off-type—pointing clearly to a contaminated planting source.
While it’s hypothetically possible that all three golf courses had residual ‘Ormond’ from past plantings, it is unlikely they would all mutate into the exact same off-type. True mutations would produce a wider variety of changes.
There are many greens and turf plots that have remained uniform and clean for decades. This doesn’t prove mutations never happen—but suggests they are not frequent. If they were, pure stands would not persist over long periods.
Saying “the green has mutations” implies that the grass changed spontaneously, when the real issue is more likely contamination or human error. This kind of language places blame on the plant and distracts from human practices like certification, inspection, and quality control—key components of turfgrass purity.