Are Ultradwarf BermudagrassCultivars Mutating?Do the industry rumors that ultradwarf cultivars mutatemean that your putting greens will deteriorate?BY J. EARL ELSNER

Inthe late 1990s, ultradwarf• •bermudagrass cultivars challenged

the dominance of Tifdwarf onwarm-season golf courses. In 2008,they are the cultivars of choice on amajority of southern golf courses.Their green speed, smoothness, andfirmness delight golfers. The apparent

absence of mutations encourages super-intendents. Ultradwarf cultivars areplanted on more than 14,000 greens,and it does not appear that the puttinggreens are developing off-type patchesor deteriorating surface quality likeTifdwarf. There are examples of collarencroachment by Tifway and other

cultivars. There are a few situationswhere plants from previous puttinggreens have survived and very fewsituations where contaminants wereintroduced from production fields ornurseries. Ten years and 14,000 greenswith very few contamination issues is aremarkable accomplishment.

Mutations disrupt surface putting quality due to the ensuing contamination.

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However, it has not been uncommonto find apparent mutant off-type plantsin ultradwarf production fields. Usually,but not always, these are individualpatches that are tennis ball to basket-ball size. The morphology varies andis similar to typical off-type plants inTifgreen and Tifdwarf putting greensand production fields. So the questionbecomes - why do ultradwarfmutations survive in production fields,but not in putting greens?

This article considers several ques-tions about mutations in bermudagrassputting green cultivars. Hopefully, itwill relieve superintendent concernsthat ultradwarf green surfaces willdeteriorate like Tifgreen and TifdwarfAn important point is to encouragecontinued diligence by growers andcertification agencies.

All DNA-based organisms havemutations, some more than others.Germ line nuclear DNA mutations arean important source of heritable char-acteristics used to develop superiorcultivars. Mitochondrial DNAmutations are the basis of Darwinianevolutionary models, which suggestthat modern humans have a commonfemale African ancestor and supporttheories about human migration routesout of Africa. Somatic DNA mutationsare the source of nectarines, naveloranges, novel ornamental plants, aswell as Tifdwarf (Burton, 1965) andthe ultradwarfs.

Discussions about mutations inputting greens cause fear and dread,but with the absence of somatic muta-tions, Tifdwarf and the ultradwarfswould not exist. None of the many

A stoloniferousor above-ground stemmutation isobserved at anultradwarfproduction field.These mutationscan occur invariousmorphologicalforms, butcertificationagencies andproducers workhard to ensurethese rarelyappear onputting greens.

thousand C. dactylon x C. transvaalensisseedlings in Drs. Glen Burton (1971),Wayne Hanna, and Charles Taliaferro'sprograms has equaled Tifdwarf or theultradwarfs' close mowing tolerance.Therefore, mutation breeding andselection of naturally occurringmutants in the Tifgreen complex hasbeen necessary for the development ofcultivars capable of providing fastgreen speeds and surface qualityrequired by golfers.

In the grand scheme of vegetativeturf grass propagation, the number ofnaturally occurring somatic mutationevents resulting in different plantmorphology is variable, but quitesmall. Caetano-anolles described theTifgreen genome as unstable andcalculated somatic mutation eventsin the Tifgreen complex to be less

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than 1 per 108 nucleotide generations(Caetano-anolles, 2002). On the otherhand, the Tifway genome was describedas being stable. Caetano-anolles' dataconfirm the extensive experience withFoundation and other Tifway nurserieswhere mutation occurrences havenever been documented. Thus far, alloff-types that have been investigated inTifway plantings have been contami-nants introduced from outside sources.

One mutation event in 108 nucleo-tide generations seems to be an almostnegligible number. However, if theassumption is made that each bermuda-grass stolon node (a node has thepotential of at least two lateral budsand each lateral bud equals one nucleo-tide generation) represents one nucleo-tide generation, then considering thenumber of nodes in a production fieldor putting green, it should not be sur-prising that mutations may be an issuein Tifgreen and its derivative ecotypes.This simple correlation also emphasizesthat freqently harvested sprig fields havea higher risk of mutations as comparedto the relatively stable putting greenenvironment. In a production field,massive numbers of vegetative buds areproduced after each harvest. Each timea new vegetative bud forms, chromo-somes are at risk to have changed,which can give rise to a new plantwith different morphology and growthcharacteristics. Fortunately, a majorityof mutations are not competitive anddo not persist in the population, butthose that do persist can causeconsiderable havoc.

This author has seen examples ofmany of the morphological typesdescribed by Burton and Powell (1971)in turf farms and putting greens aroundthe globe. They vary from growthrates like Tifgreen to more dwarf thanthe ultradwarfs, leaf color from canaryyellow to intense dark green, prolificseedhead production to almost anabsence of seedheads, long narrow toshort broad leaf blades, along withdifferent responses to herbicides, hightemperatures, and cool nights. It

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appears that an almost infinite numberof morphological types can occur inthe Tifgreen complex.

There is a great deal of evidence thatthe mutation potential of the Tifgreencomplex is maintained in othermembers of the family, whether it isTifdwarf, an ultradwarf, or otherselections. Also, research in severallaboratories utilizing various DNAfingerprint techniques has consistentlyshown that each of the current ultra-dwarf cultivars is closely related toTifgreen and Tifdwarf and distantlyrelated to the more genetically stableTifway (Goatley et al., 2005; Williams,2003). Therefore, it should not beunexpected that mutations occur inultradwarf production fields. Fieldinspections support these conclusions.

Theoretically, the survival of amutant depends on its selective advan-tage or disadvantage relative to themanagement of the matrix populationwhere it occurs. Experience has shownthe following relationships:• When an ultradwarf type plantdevelops from a mutation event in aTifdwarf putting green, the moredwarf plant should have a selectiveadvantage for mowing height. If otherphysiological characteristics are at leastequal, the mutant produces an expand-ing, dense, thatchy, and grainy circularpatch. It also may contaminate otherputting green areas via mechanicaloperations (vertical mowing, aeration,and cup placement).• If contaminant sprigs with growthcharacteristics similar to Tifgreen orTifdwarf are planted in a newlysprigged ultra dwarf putting green, thecontaminant will grow very rapidlyand out-compete the ultradwarfWhen mowing height is lowered, thecompetitive relationship shifts in favorof the ultradwarf Ultimately, the non-ultradwarf plants will be suppressed bymowing and may disappear entirely,but in the interim, putting surfacequality may be compromised.

The preponderance of evidencesupports the premise that successful

mutations occur in ultradwarf produc-tion fields, but mutants have not beenan issue when the event occurs inultradwarf putting greens. The reasonfor the ultradwarf mutants' apparentlack of competitiveness in puttinggreens is not known. It may be thatthey have physiological or other dis-advantages, preventing the establish-ment of a distinct population in theputting green. It may be that themutants' colors and leaf morphologyunder greens management is similar tothe ultradwarf cultivar such that theyblend in and do not disrupt the uni-form putting green surface. Or, it maybe a combination of these factors andothers, depending on the characteristicsof specific mutations.

Ultradwarf mutations in sprig fields,however, are and should be a cause forconcern.• If a mutant plant with growthcharacteristics similar to Tifgreen orTifdwarf becomes established in anultradwarf production field, each timethe sprig field is harvested, the moreaggressive plant will expand faster thanthe ultradwarf After multiple harvestsby traditional sprig digging equipment,the aggressive plant will likely becomethe dominant type.• If a mutant plant with growthcharacteristics similar to or more dwarfthan an ultradwarf occurs in a sprigfield, the mutant may persist, butshould not expand. However, if thismutant has significantly different leafcolor and contaminates harvestedsprigs, it may be noticeable in the newultradwarf green.

Meticulous roguing is required tomaintain genetic and morphologicaluniformity in ultradwarf productionfields. One of the keys to the lowfrequency of contamination in ultra-dwarf putting greens is the attentionthat producers and certification agencieshave placed on morphological uni-formity as compared to the emphasisduring most of Tifdwarf's tenure. It isimportant for turf growers and certifi-cation agencies to be even more atten-

tive as the ultradwarf cultivars becomeolder. The mutation potential shouldnot change, but each new successfulmutant adds to the potential cumula-tive off-type load that may be presentin a production field. Each must beidentified and removed, or else theremay be a disaster waiting to happen.

The final question: When is avariant plant considered to be an off-type? Observant superintendents manytimes see plant variation in their ber-mudagrass putting greens and want aDNA fingerprint. The rule of thumbin the Georgia Certification program,almost a paradigm, is that DNA finger-prints are tools but not necessarily thefinal answer. if a plant looks different,grows differently, or reacts differently, it is aniff-type. In certain situations the micro-environment will cause confusionsuch that a normal plant may take oncharacteristics of an off-type. Underthese conditions, a uniform pot grow-out is used to confirm whether it is anoff-type by comparison to a knownstandard of the cultivar.

A recent situation with seashorepaspalum illustrates the reason thatmorphology and growth characteristicsmay be more effective than DNAfingerprints for labeling a plant an off-type. A putting green had off-colorpatches of suspect off-types. Threesamples were obtained from areas withdifferent color or growth characteristics.The DNA fingerprints indicated thatone was different from the matrixcultivar, one was slightly different, andone was indistinguishable. However,all three plants met the off-type defini-tion because they had different mor-phological and/or growth character-istics. The opposite also occurs when aDNA fingerprint may falsely label aplant as an off-type because the finger-print utilized polymorphorisms thatdo not influence plant growthcharacteristics.

In conclusion, ultradwarf puttinggreens have a good track record ofproviding excellent putting surfaceswith no indication of deterioration due

to putting green mutations. Ultradwarfsod and sprig producers have been dili-gent in maintaining genetic, morpho-logical, and physiological uniformity.Diligence will have to be increased ifthe next ten years are to be as success-ful as the first ten years of ultradwarfsprig and sod production.

REFERENCESGlenn W. Burton, J. Earl Elsner. 1965.Tifdwarf - A new bermudagrass for golfgreens. USGA Green Section Record. 2:8-9.

Glenn W. Burton, Jerrel B. Powell. 1971.Better bermudagrasses to meet golf's demands.USGA Green Section Record. November.9(6):9-11.

G. Caetano-anolles. 2002. High genome-widemutation rates in vegetatively propagatedbermudagrass. Molecular Ecology. 8:1211-1221.J. M. Goatley, Jr., H. W. Philley, J. v. Krans,E. A. Van Santen, L. Capo-chichi, andD. Davis. 2005. The genetic stability of sixbermudagrasses as affected by chronicexposure to dinitroaniline herbicides. CropScience. 45:1504-1510.Neil Ray Williams. 2003. PCR-based poly-morphisms in bermudagrass (Cynodon spp.).M.S. thesis. University of Florida.

DR. EARL ELSNER is retired director if theGeorgia Foundation Seed and TuJjgrassprogram. He currently advises tuJjgrassproducers, superintendents, and Universityif Georgia cultivar licensing authorities onmatters of tuJjgrassproduction and genetics.

Tifway bermudagrass encroachment into an ultradwarf putting green surface occasionally happens, butit is very rare. Ultradwarfs usually have a significant advantage over bordering turfgrasses at lowmowing heights on putting greens.

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