FOR RICHER, FOR POACultivar development of greens-type Paa annua.

by DR. DAVID R. HUFF

Genetic diversity abounds in the multiple selections of Poa annua One goal of thePenn State University breeding program is to provide golf course superintendentswith a commercially available seed source of greens-type Poa annua

POR RICHER, for poorer. Insickness and health .... " Thesesimple words underscore one of

life's greatest commitments. It also de-scribes the golf course superintendent'sdaily commitment to maintaining golfgreens that are comprised of Poaannua.

Poa annua has been part of the golfindustry for a long time, probably eversince the inception of the game. Some-time around the early 1900s, bentgrassbecame the chosen or preferred grass togrow and maintain on golf course putt-ing greens. Yet, Poa annua continuesto be a major component, and in manycases a dominant component of golfcourse putting greens.

By virtue of its prolific seed headproduction, occurring under even theclosest of mowing heights, Poa annuahas been able to evolve a competitiveedge against creeping bentgrass interms of shoot density, verdure bio-mass, and photosynthetic surface area.Moreover, under shady, moist, cooltemperature conditions, Poa annuathrives and continues to gain a com-petitive edge against bentgrass until itultimately dominates many golf greenputting surfaces.

Observations such as these haveplayed a key role in initiating PennState's breeding program for develop-ing commercial sources of Poa annuafor use on golf greens. Yet some peopleview this idea as ridiculous; Poa annuais, after all, the enemy, isn't it? Never-theless, an underlying truth is undeni-able: superintendents who have Poaannua greens simply do not have ahope of obtaining a seed source for thetypes of Poa annua that are adaptedto their golf green environments for usein routine oversee ding, repair work, ornew green construction. This industryneed is the motivation and spirit thatdrives our breeding program towardswhat we hope will produce commer-cially available seed sources of greens-type Poa annua. Only time will tell ifwe will be successful.

Natural SelectionNature, coupled with the intense

selection pressure provided by super-

intendents and golfers, has performeda tremendous amount of evolutionarychange in Poa annua during the past100 years - from the wild and weedyannual bluegrasses that first invade agreen, to the highly specialized, high-quality, greens-type Poa annua that wecan find today. Our breeding programutilizes this natural evolutionaryprocess by collecting and screening itsproducts. We regularly collect samplesfrom old, closely mowed greens fromseveral regions of the U.S. and Canada.

Due to the reproductive biology ofannual bluegrass, we believe this is afruitful approach. Poa annua has aself-pollinating type of breeding systemthat results in true breeding strainsthrough inbreeding. Eggs within theflowers (florets) are often fertilized be-fore the florets ever open (cleistogamy).Such an inbreeding system of sexualreproduction is unique among thegrasses we typically use for turf, and ismost similar to that of wheat or soy-beans. Poa annua also is a polyploidgrass species, meaning that each of itscells carries multiple copies of itsancestors' chromosomes. Polyploidy

is rare among animals and insects,but is common among plants. Amonggrasses, polyploidy is often the normalstate of being.

Poa annua is believed to have hadtwo ancestors, Poa supina and Poainfirma. Both of these species are con-sidered to be diploid organisms, andeach carries 14 chromosomes (denotedas 2n=2x=14 chromosomes). Becausethey are different species, the 14 chro-mosomes are very different betweenspecies and, upon hybridization, resultin sterile offspring. A similar eventhappens when a donkey is mated witha horse to obtain a mule, which also issterile. In plants, however, and prob-ably due to their modularity, eventsmay occur which restore fertility bydoubling all of a cell's chromosomes.This is the situation with Poa annua.The two species, Poa supina and Poainfirma, mated to produce a sterilehybrid plant (In=2x=14 chromosomes)whose chromosome number spon-taneously doubled to yield Poa annua(2n=4x=28 chromosomes).

Such hybridization and doublingevents generate extreme amounts of

JANUARY IFEBRUARY 1999 11

Challenges such as seedhead production, disease and insect resistance, and rootingpotential need to be resolved in the breeding program.

variability (i.e., 100%). The level of thisvariability is reduced by 50% within aparticular strain after every generationof self-pollination. Thus, after the firstgeneration of selfing, the amount ofvariability is reduced to 50%; thesecond reduces it to 25%; the third to12.5%, and so on. A similar reductionin variability is necessary after makinghybrids between distinct, true-breed-ing strains of greens-type Poa annua.Thus, after mating two different strainsof Poa annua, it takes a minimum ofsix to eight generations before we re-gain strains that are uniform, stable,

and true breeding. In producing onegeneration every two years, which in-cludes some limited trial evaluation, itis easy to see that artificially breedingimproved strains of Poa annua is along-term process. However, much ofthis work has already occurred on oldgolf greens because of natural hybridi-zations, close mowing heights, thetraffic provided by golfers, and the com-petition among all grasses for thelimited resources of a golf greenenvironment. With every generation,Poa annua has been evolving to toler-ate low cutting heights and increasedfoot traffic. This evolutionary processhas resulted in strains we call greens-type Poa annua.

Such greens-type Poas probablywere not present back in the early1900s when bentgrass was chosen asthe grass to plant on golf course puttinggreens because it has taken the past 100years of evolution and competition to

12 USGA GREEN SECTION RECORD

produce them. In fact, the selectionpressures of the green environment areso intense that we believe we are start-ing to observe a "reverse" evolutionaryprocess that is resulting in the appear-ance of the original interspecific hybrid(In=2x=14 chromosomes). Theseunique specimens have only half theamount of DNA of Poa annua andrepresent some of the densest, finest,highest quality strains we've observedto date. Like the mule, however, theseunique strains are sterile, and ourbreeding program is investigating re-search avenues that may enable us to

restore fertility while retaining theirfavorable attributes. Thus, in additionto simply collecting samples of Poaannua that have evolved naturally ongolf greens, we also have begun thelong-term process of actively breedinggreens-type Poa annuas using tradi-tional methods and some of the newermolecular genetic technologies.

Growing Limitations

Just as the farmer who decided togrow dandelions for the natural foodmarket discovered, when a weed isgrown as a crop you find out yourindestructible weed has a list of prob-lems all its own that need to be over-come. One of the major limitations ofgrowing Poa annua is its limited rangeof favorable growing temperatures. Poaannua tends to grow poorly whentemperatures are either too hot or toocold. As part of our breeding program,

we are actively investigating the varia-bility within the species for toleranceto extreme temperatures. Working ontemperature tolerance in plants is notas straightforward as it might seem.To simply plunge a grass plant into anextreme temperature does not allow theplant's natural defense mechanisms toincrementally adjust. In order to gaininsight into Poa annua's tolerancemechanisms, we first need to acclima-tize the plants before exposing them toextreme temperatures. To evaluate forcold tolerance, the Poa annuas arepre-hardened at 2°C for one to twoweeks, followed by -2°C for anothertwo weeks. Temperatures are thenlowered down to critically cold levels.

This cold-tolerance research is beingperformed as a collaborative researchproject with the Canadian TurfgrassResearch Foundation (CTRF), LavalUniversity at Quebec, and AgriculturalCanada at 8t. Foy. At Laval University,co-investigator Julie Dionne's prelimi-nary findings suggest that there aredifferences among greens-type Poaannuas in their ability to toleratecritically cold temperatures. The leastcold-tolerant Poa annua showed a50% survival rate at 1.4of, while themost cold-tolerant Poa annua showeda 50% survival rate down to -8.3°F.These tolerances are far less thancreeping bentgrass, which is capable ofdemonstrating 50% survival down to-18.4oF.Only by discovering differencesamong Poa annuas will we be able todiscover the underlying genetic andphysiological mechanisms responsiblefor these differences, which might en-able us to improve Poa annua's in-herent cold-tolerance mechanisms.

Throughout our work, it has beenhelpful to look at other systems of coldtolerance. Fortunately, one of the onlytwo plants known to grow in Antarc-tica happens to be a grass - Antarctichairgrass (Deschampsia antarctica).Antarctic hairgrass has quite literallyonly a few hours each day during themiddle of summer in which tempera-tures get above freezing, enablingphotosynthesis to occur. The remark-able finding is that there seems to be no"silver bullet" cold-tolerance mecha-nism at work inside Antarctic hairgrass.Rather, cold tolerance is ascribed toa substantial ability to store naturallyoccurring carbohydrates called fructans.

We also have begun to observe dif-ferences in fructan levels among thePoa annuas and are currently corre-lating this information with our cold-tolerance studies. If it's discovered that

fructan storage is a major component ofcold tolerance in Paa annua, as itappears to be in Antarctic hairgrass,then we may be able to breed for theability to store fructans and therebybegin to realize improved tolerance tocold temperatures in Paa annua.

Tolerance to IceAnother important area of our cold-

tolerance research is to determine Paaannua's tolerance to ice coverage.Many factors may be related to Paa'sability to tolerate ice coverage. Crownhydration, lack of oxygen, release andbuildup of toxic gases, the frequencyand modulation of freeze-thaw cycles,duration of coverage, and carbohydratereserves are all potential factors thatmay work independently or may inter-act to yield the observation that, ingeneral, ice coverage often kills Paaannua.

Our research to date has been in-conclusive. During some experimentsthe Paa annua dies, in others it doesnot. Could other factors be responsibleor interacting with those previouslymentioned? What are the hydro-dynamics at the interface between thesoil and ice? Is it just ice or is it acombination of ice over a saturatedsoil that kills Paa? Are native soilsmore susceptible to ice damage thanare sand-based greens?

Currently, we have more questionsthan answers. Even so, we know thatvisual differences in ice may appear. Forexample, warm water freezes slowlyand is generally free of trapped air,making it appear clear or transparent(i.e., black ice); cold water freezesmore quickly and often has pocketsof trapped air which make it appearcloudy or white. Perhaps it is notwhether ice is black or white that isimportant, but rather how quicklywater freezes and what the potential isfor soil drainage to occur before icedevelops. We are only beginning toestablish those conditions in which weare capable of killing Paa annua re-peatedly with ice coverage at slightlyfreezing temperatures (approximately27°P). Once these conditions areestablished, we will begin to screen thePaa annua collection for differentialtolerances. After tolerant and suscep-tible strains are identified, we will beginto examine physiological differences toexplore ways in which to enhance Paaannua's tolerance to ice coverage.Heat Tolerance

On one of my collection trips alongcoastal Virginia, a superintendent re-

marked that "Paa annua is the greatestgrass ... for nine months of the year."Heat tolerance and Paa annua mayseem like contradictory terms, but thesuperintendent who made that state-ment had greens consisting of 80% Paaannua. Many northern regions wherePaa annua dominates also experiencesome measure of summer heat stressduring July and August. Thus, anyimprovement that might be madetowards enhancing the heat toleranceof greens-type Paa annua wouldbenefit those superintendents andgolfers who have Paa annua greens.

Generation after generation, Poa annuahas continuously evolved to gain acompetitive edge and improved shootdensity.

Like the above two projects, screen-ing for differences in heat toleranceamong the collections is our startingpoint. Heat benches containing sandroot zones and adjustable heating unitsserve as our coliseum where Paaannua is forced to wage battle againsthigh temperatures (approximately113°P). Will Paa annua with deeperroots win out, being able to transpireand thus cool off more effectively, ordo some Paas have root/crown pro-teins that function slightly better atelevated temperatures? Only time willtell.

Other Complicating FactorsGreens-type Paa annua has many

additional problems that ultimatelyneed to be resolved: seed head pro-duction, disease and insect resistance,rooting potential, and determining best

management practices. Each of theseareas, as well as extreme temperaturetolerances, are beginning to be ad-dressed in our breeding program. Byscreening the increasing number of col-lected strains, and through the eventualscreening of new genetic combinationsresulting from our hybridization breed-ing program, we hope to develop largeenough supplies to offer turfgrass sci-ence colleagues around the country achance to test and evaluate the elitestrains of greens-type Paa annua. Theultimate goal of developing commer-cially available sources of greens-typePaa annua is not to replace bentgrassas a preferred grass for putting surfaces,but rather to offer an additional toolfor superintendents to have at theirready, especially in regions and climateswhere Paa annua is simply a betterchoice of grass for use as a puttingsurface. Por many, there is no otherchoice than to commit to "Por richer,for Paa."

ReferencesBeard, J. B. 1964. Effects of ice, snow, andwater covers on Kentucky bluegrass, annualbluegrass, and creeping bentgrass. Crop Sci.4:638-640.Beard, J. B. 1970. An ecological study ofannual bluegrass. USGA Green SectionRecord, March, pp. 13-18.Beard, J. B. 1996. Low-temperature kill andice sheets. Golf Course Management, May,pp.60-64.Beard, J. B., P. E. Rieke, A. J. Turgeon, andJ. M. Vargas. 1978. Annual bluegrass (Poaannua L.) description, adaptation, culture,and control. Res. Rep. 352. Michigan StateUniversity, East Lansing. 31 p.Bittenbender, H. C., and G. C. Howell, Jr.1974. Adaptation of the Spearman-Kiibermethod for estimating Tso of cold-stressedflower buds. J. Amer. Soc. Amer. Sci.99:187-190.Bjorkman, 0., M. R. Badger, and P. A.Armond. 1980. Response and adaptation ofphotosynthesis to high temperatures. p.233-249. In Adaptation of plants to waterand high-temperature stress. John Wileyand Sons Publishers, Toronto.Castonguay, Y, S. Laberge, and P'-Nadeau.1993. Freezing tolerance and alteration oftranslatable mRNAs in alfalfa hardened atsubzero temperatures. Plant Cell Physiol.34:31-38.Cordukes, W E. 1977. Growth habit andheat tolerance of a collection of Poa annuaplants in Canada. Can. J. Plant Sci. 51:1201-03.

Dionne, J., and Y Desjardins. 1996. What'shappening under the blanket. Greenmaster,November.

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Edwards. J. A., and R.I.L. Smith. 1988.Photosynthesis and respiration of Colo-ban thus quitensis and Deschampsia ant-arctica from the Antarctic. British AntarcticSurvey Bulletin 81:43-63.

Fehr, W R 1991. Principles of CultivarDevelopment. Vol. 1. Theory and Tech-nique. Iowa State University. Macmillan. p.536.

Gibeault, V. A. 1970. Perenniality in Poaannua L. Ph.n Dissertation. Oregon StateUniversity, p. 124.

Hetherington, P.R, B. n McKersie, and A.Borochov. 1987. Ice encasement injury tomicrosomal membranes from winter wheatcrowns. Plant Physiol. 85:1068-1072.

Huff, n R 1996a. Poa annua for golfcourse greens. Grounds Maintenance,January, pp. G2-G 10.

Krause, G. H., and E. Weis. 1984. Chloro-phyll fluorescence as a tool in plant physi-ology. II. Interpretation of fluorescencesignals. Photosynth. Res. 5:139-157.

Krause, G. H., and S. Somersalo. 1989.Fluorescence as a tool in photosynthesisresearch: application in studies of photo-inhibition, cold acclimation, and freezingstress. Phil. Trans. R Soc. Lond. B 323:281-293.

Li, P. H. 1984. Subzero temperature stressphysiology of herbaceous plants. Hort. Rev.6:373-416.Lush, W. M. 1988. Biology of Poa annuain a temperate zone golf putting green(Agrostis stolonifera/Poa annua). II. Theseed bank. Journal of Applied Ecology25:989-995.McKersie, B. n, and Y. Y Leshem. 1994.Anaerobic stress-flooding and ice-encase-ment. p. 15-54. In Stress and stress copingin cultivated plants. Kluwer AcademicPublishers, Boston.Meyer, W A., J. A. Murphy, D. A. Smith.Response of cool-season turfgrass to anovel traffic simulator. 89th ASA-CSSA-SSSA. Anaheim, California. AgronomyAbstracts.Minner, D. D., P. H. Dernoeden, D. J.Wehner, and M. S. McIntosh. 1983. Heattolerance screening of field -grown cultivarsof Kentucky bluegrass and perennial rye-grass. Agron. J. 75:772-775.Mowforth, M. A., J. P. Grime. 1989. Intra-population variation in nuclear DNAamount, cell size, and growth rate in Poaannua L. Functional Ecology 3:289-294.Osteryoung, K. W, and E. Vierling. 1994.Dynamics of small heat shock proteindistribution within the chloroplasts ofhigher plants. Journal of BiologicalChemistry 269:28676-28682.

Smillie, R M., and S. E. Hetherington.1983. Stress tolerance and stress-inducedinjury in crop plants measured by chloro-phyll fluorescence in vivo. Plant Physiol.72:1043-1050.Tompkins, D., C. Bubar, E. Toews, and J.Ross. 1995. Physiology of low temperatureinjury with emphasis on crown hydration inPoa annua L. In Prairie turfgrass researchcentre annual report 1995.Wallner, S. J., M. R Becwar, andJ. D. Butler.1982. Measurement of turfgrass heat toler-ance in vitro. J. Hortic. Sci. 107:608-613.Warwick, S. 1. 1979. The biology ofCanadian weeds. Poa annua L. Can. J.Plant Sci. 59:1053-1066.

Principal Project InvestigatorsDr. Yves Desjardins, Laval UniversityMs. Julie Dionne, Laval UniversityDr. Yves Castonguay, Agriculture Canada

Research Center, Ste-FoyDr. Daniel Knievel, Penn StateMr. George Hamilton, Penn StateMr. Eric Lyons, Penn StateMr. Roy Knupp, Penn StateMr. Jim Ross, Prairie Turfgrass Research

CentreMany thanks to the numerous golf coursesuperintendents who have allowed collec-tions of Poa annua from their greens andto the USGA Green Section agronomistswho assisted with the collection trips.

Dr. David Huff has collected thousands of Poa annua samples throughout the UnitedStates. A pile of Poa annua this large will make any plant breeder smile.

14 USGA GREEN SECfION RECORD

Donating Poa annuaIfyou or someone you know has greens-type Poa annua and would like to haveits merits examined, the PSU Poa annuabreeding program would like to receiveyour samples. Begin by collecting one ortwo aerification tine cores from each"patch" you wish to sample (no limithere), wrap in a moist paper towel,enclose in a zip-lock bag, and label eachbag with your course name and holelocation (example: Oakmont 18G). Sendby overnight mail to:David R HuffAssistant ProfessorTurfgrass Breeding and GeneticsDept. of Agronomy, 116ASI Bldg.Pennsylvania State UniversityUniversity Park, PA 16802Phone: 814-863-9805Fax: 814-863-7043E-Mail: drhI5@psu.edu

Poa annua is a reality on most cool-seasongolf courses in America. DR DAVIDHUFF, assistant professor in turfgrassbreeding and genetics at PennsylvaniaState University, hopes to improve onwhat's available.