Developing Annual Bluegrass Cultivars for Putting Greenshigh shoot density that contributes to ......

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Developing Annual Bluegrass Cultivars for Putting Greens Work continues at Penn State University to tame this highly variable species. BY DAVID R. HUFF producing new shoots from the upper nodes of the decumbent shoots. In addition, the perennial form produces a high shoot density that contributes to the appearance of a rather tight turf. The perennial biotype of annual blue- grass also is more restricted in the timing of seed formation than the annual form, and it allocates more of its resources (photosynthates) into vegeta- tive growth rather than seed produc- tion. As a result, the perennial form is almost exclusively found growing in closely mowed turfS such as old, estab- lished golf greens. Thus, one's percep- tion of whether it is a weed (either lots of smaillime-green tufts on a golf green Tolerates close mowing heights low shoot density, course texture. tall stature UgIy,bad Table I Comparison of characteristics typically associated with either the annual or perennialJonns of Poa annua "Annual" Annual Bluegrass •• ~t Annuai ~ Favored by constant surface disruption r=avorect'by su~e st8b.iiq(lktJe d~)'oii<':: 'w!l' ~J}i Produces lots of seed Produces litde to no seed ' .o:~~ Dominates soil seed bank Scarce in the soU seed bank j 0" Quick to germinate, quick to flower Slower to flower Extremely sensitive to environmental Ukely more tolerant of environmental stresses (heat, cold, drought) stresses (heat, cold, drought) it t~'. [ .• ,'~<; ~ti.,r~;:1 , Easier to kill with chemicals, although More likely to tolerate herbicides,'~. r;;,'ft, numerous reportS of.,~ ~ce .. !!!. :;::~. A" j~.o. Individuals reprOduCeth~.a 0 ,'Individuals i"eproducedutmg ,a~' P:l '.growing season, during a season (typJcaI~ $I>ri~ only) ,,'W : Most individuals die within a.season Most individuals INe multiple seasonsan4, perhaps some.8re ,long-li\Ied 0 , '. Lots of~ variabIe-coIor patdies on a golf green Adapted to dose mowing heights I,' High shoot density. fine teXture. short statUre Beautiful. good variable species. It contains forms that behave as annuals and other forms that behave as long-lived perennials. Traits typically associated with either annual or perennial forms are listed in Table 1. Basically, the annual form has a bunch-type, upright growth habit of low shoot density and is found in open fields, orchards, and meadows. Plants of the annual form tend to behave more as annuals in that they are non-creepers and are prolific seed producers. The perennial form has either an upright growth habit of diminutive stature or a more prostrate, spreading growth habit capable of rooting and VARIABLE WITH A WORLDWIDE DISTRIBUTION Paa annua is one of the world's most widely distributed invasive weed species and, in all its forms, is found on every continent. The mechanisms that enable this grass species to disseminate its progeny so widely and enable it to survive, adapt, and persist in such a wide range of environmental conditions are currently not known. One thing we do know is that Paa annua is a higWy P aaannua L., the Latin name for annual bluegrass, has long been recognized for providing high quality turf of fine texture and high shoot density that is uniform and tolerant of close mowing. 1 In 1927, legendary USDA agronomists Piper and Oakley14 described the value and high quality of Paa annua for golf course putting greens. More recently, Warwick 16 observed that if grown in a mono culture, Paa annua provides an excellent putting surface. However, not everyone reached the same conclusion concerning the utility of Paa annua. While some turf grass agronomists have encouraged the use and cultivation of Paa annua as turf,7,15,17 others have focused on its eradication as a weed. 2 ,12In fact, most instances of Paa annua literature describe the grass as an invasive weed whose eradication should be pursued at all costs. This article focuses on the utility and genetic improvement of Paa annua for use as putting surfaces. 12 GREEN SECTION RECORD

Transcript of Developing Annual Bluegrass Cultivars for Putting Greenshigh shoot density that contributes to ......

Page 1: Developing Annual Bluegrass Cultivars for Putting Greenshigh shoot density that contributes to ... tion of whether it is a weed (either lots of smaillime-green tufts on a golf green

Developing Annual BluegrassCultivars for Putting GreensWork continues at Penn State Universityto tame this highly variable species.BY DAVID R. HUFF

producing new shoots from the uppernodes of the decumbent shoots. Inaddition, the perennial form produces ahigh shoot density that contributes tothe appearance of a rather tight turf.The perennial biotype of annual blue-grass also is more restricted in thetiming of seed formation than theannual form, and it allocates more of itsresources (photosynthates) into vegeta-tive growth rather than seed produc-tion. As a result, the perennial form isalmost exclusively found growing inclosely mowed turfS such as old, estab-lished golf greens. Thus, one's percep-tion of whether it is a weed (either

lots of smaillime-green tufts on a golf green

Tolerates close mowing heightslow shoot density, course texture. tall statureUgIy,bad

Table IComparison of characteristics typically associated

with either the annual or perennialJonns of Poa annua"Annual" Annual Bluegrass ••~t Annuai ~Favored by constant surface disruption r=avorect'by su~e st8b.iiq(lktJe d~)'oii<'::

'w!l' ~J}iProduces lots of seed Produces litde to no seed ' .o:~~Dominates soil seed bank Scarce in the soU seed bank j 0"

Quick to germinate, quick to flower Slower to flowerExtremely sensitive to environmental Ukely more tolerant of environmentalstresses (heat, cold, drought) stresses (heat, cold, drought) it t~'. [

.• ,'~<;~ti.,r~;:1,Easier to kill with chemicals, although More likely to tolerate herbicides,'~. r;;,'ft,numerous reportS of.,~ ~ce .. !!!. :;::~. A"

j~.o.

Individuals reprOduCeth~.a 0 ,'Individuals i"eproducedutmg ,a~' P:l'.growing season, during a season (typJcaI~ $I>ri~ only) ,,'W :

Most individuals die within a.season Most individuals INe multiple seasonsan4,perhaps some.8re ,long-li\Ied 0 , '.

Lots of~ variabIe-coIor patdieson a golf greenAdapted to dose mowing heights I,'

High shoot density. fine teXture. short statUre

Beautiful. good

variable species. It contains forms thatbehave as annuals and other forms thatbehave as long-lived perennials.

Traits typically associated with eitherannual or perennial forms are listed inTable 1.Basically, the annual form has abunch-type, upright growth habit oflow shoot density and is found in openfields, orchards, and meadows. Plants ofthe annual form tend to behave more asannuals in that they are non-creepersand are prolific seed producers.

The perennial form has either anupright growth habit of diminutivestature or a more prostrate, spreadinggrowth habit capable of rooting and

VARIABLE WITH AWORLDWIDE DISTRIBUTIONPaa annua is one of the world's mostwidely distributed invasive weed speciesand, in all its forms, is found on everycontinent. The mechanisms that enablethis grass species to disseminate itsprogeny so widely and enable it tosurvive, adapt, and persist in such a widerange of environmental conditions arecurrently not known. One thing we doknow is that Paa annua is a higWy

Paaannua L., the Latin name forannual bluegrass, has long beenrecognized for providing high

quality turf of fine texture and highshoot density that is uniform andtolerant of close mowing.1 In 1927,legendary USDA agronomists Piperand Oakley14 described the value andhigh quality of Paa annua for golfcourse putting greens. More recently,Warwick16 observed that if grown in amono culture, Paa annua provides anexcellent putting surface.

However, not everyone reached thesame conclusion concerning the utilityof Paa annua. While some turf grassagronomists have encouraged the useand cultivation of Paa annua as turf,7,15,17others have focused on its eradicationas a weed.2,12In fact, most instances ofPaa annua literature describe the grassas an invasive weed whose eradicationshould be pursued at all costs. Thisarticle focuses on the utility and geneticimprovement of Paa annua for use asputting surfaces.

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PENN STATE'SBREEDING PROGRAMWhen the annual bluegrass breedingprogram was initiated in July 1994 thou-sands of Paa annua samples were col-lected from existing golf course greens.To date, the project has collected andevaluated tens of thousands of Paa annuaplants. These early selections exhibited awide range of genetic variation innearly every imaginable trait, includingtiller density, color, seedhead produc-tion, disease resistance, and environ-mental stress tolerance. Subsequent col-lectio"ns have yielded similar variability.

Improvements to these initial collec-tions have been achieved by successfullyapplying several fundamental principlesof plant breeding. Primarily, the breed-ing process has improved turf qualityregarding not only shoot density, color,and uniformity of appearance, but alsoin increased tolerance to several biotic(disease) and abiotic (environmental)stresses.

Number of DaughterTIliers1-3

.4-8

>9

i ,

After an effluent water line broke at one of the trial sites and the plots went unwatered for ten days,plot differences were evident. The Penn State annual bluegrass (back right) was better able to handlethe lack of water when compared to the local, native annual bluegrass plot (back left).

(anthesis) of the parent tiller. The resultsare presented in Table 2 and indicatethat Paa annua plants evolve an increas-ingly perennial nature as the level ofturfgrass management increases. Thisprocess continues on the golf greenuntil eventually plants become entirelyperennial and lose the ability to setviable seed altogether. It is these laterclasses of evolutionary products, thosethat still set viable seed and are higWyperennial and those that do not setviable seed and are entirely vegetative,that have served as the raw material forcultivar development in the Penn StatePaa annua breeding program.

Tabie 2Number of daughter tillers produced at the

time of flowering (anttlesis) of the parent tiller

RoughFairwayGreens

Source of POD annua

~:l\~:l,

annual or perennial forms) or a valuableputting surface (a higWy evolved peren-nial form) depends on which form ispresent in the turf

ANNUAL OR PERENNIAL?The problem in designating an annualbluegrass plant as either an annual ora perennial is that there is a range orspectrum of variability of what ecolo-gists call "life-history characteristics"that exists within the species. One wayto measure the perennial nature of aparticular Paa annua plant is to deter-mine if it grows faster than it dies. Inother words, one needs to consider if agrowing shoot (also known as a tiller,the basic unit of a grass plant) replacesitself before it flowers, because once atiller flowers, it dies. And if it does, howmany replacements does it produce?

If a tiller replaces itself with just asingle daughter tiller before it flowers(i.e., a one-to-one replacement), thatwould seem to be a precarious positionfor a perennial to be in because anynumber of mishaps or events couldeasily eliminate the one vegetative off-spring. In addition, most of the tiller'senergy would be invested in seed versusa single vegetative tiller offipring, andso the parent tiller would likely be sur-vived by its seed progeny and not by itsonly vegetative tiller. This tiller wouldbe behaving as an annual plant. How-ever, if a tiller were to produce manytillers before it flowered (i.e., many-to-one replacement), it would be behavingas a perennial plant.

In experiments conducted at PennState University, we measured a rangeof annual bluegrasses for this trait bycounting the number of daughter tillers

.produced at the first sign of flowering

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Currently, the breeding programhas designated a set of the "top-12"cultivars. These cultivars currently arebeing evaluated on various golf coursesand university research facilities aroundthe world. The encouraging news frompreliminary reports is that these cultivarsare performing well, even better thanexpected. For instance, at a trial estab-lished at Barwon Heads G.C., locatedon the southern coast of Victoria,Australia, half the plots were irrigatedwith potable (drinkable) water, whilethe other half were irrigated with high-salinity effiuent water. Planted alongwith the Penn State annual bluegrasseswere plots of the local, native Foa annuaand several cultivars of creeping bent-grass, including Penn A-4, Seaside II,Mariner, and Penncross. Foa annua isknown for its inability to tolerate highsaline conditions, whereas bentgrassesare known for their ability to toleratehigh saline conditions.

The first year's data from this mul-tiple-year study (courtesy of]. Neylan,Australian Golf Course SuperintendentsAssociation) indicates that the PennState annual bluegrasses are not onlysurviving the high salinity of the effiu-ent water source, but they are demon-strating higher turf quality than bent-grasses in many instances. Moreover,during the late summer of 2004(February-March), the effiuent waterline broke and the plots were unwateredfor 10 days. The Penn State annualbluegrasses fully recovered, while thelocal native annual bluegrasses died,demonstrating improved drought resis-tance in some strains of this highlyvariable species.

STRESS TOLERANCEStress tolerance is an important factorthat contributes to perenniality. Afterall, does it really matter how muchbetter turf quality specific selectionsmay have if the plants have little or noinherent ability to tolerate environ-mental and biological stress? In order tobe perennial, turf grasses must be able tosurvive and persist month after month,

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season after season, year after year,through all kinds of heat, cold, disease,and traffic stresses, whereas plants withannual life cycles can simply die andsurvive these stressful periods as seed.

Most of what we know about Foaannua is based on the annual or less-evolved perennial types. For example,both high and low temperatures repre-sent the major environmentallimita-tions to distribution and growth of Foaannua. It is generally believed that thislack of tolerance to extreme tempera-tures makes Foa annua a weak turf for atleast some part of the year in most loca-tions. Despite this general observation,strains of Foa annua have been observedto perform well in irrigated turf areassubjected to the desert heat of Arizona(D. Kopec, 1998, pers. com.). DufP alsoreported significant differences amongstrains for heat tolerance. At the othertemperature extreme, Dionne et al.3

reported finding significant differencesamong strains for tolerance to freezingtemperatures.

Foa annua also is widely known forits susceptibility to many turfgrass dis-eases, including dollar spot (Sclerotiniahomoeocarpa),anthracnose (Colletotrichumgraminicola), and pink snow mold(Monographella nivalis). However, the Foaannua breeding program at Penn Statehas identified strains exhibiting excel-lent field resistance to anthracnose anddollar spot.6,8 Thus, while most scientificefforts regarding Foa annua have beendirected towards its eradication, control,or lack of stress tolerance, those researchefforts aimed at determining and identi-fying strains possessing improved stresstolerances have generally beensuccessful.

INVADE AND ADAPTThe evolution of Foa annua from wild,weedy, annual forms to the perennialforms adapted to golf, lawn, and athleticfield turf has been documented byplant ecologists and plant evolutionistsas a classic example of rapid micro-evolution.to,lJ,13 When Foa annua firstinvades a turf area, it typically does so as

P~Q QnnUQ exhibits a range of perenniality as shownby the number of daughter tillers produced at thetime of first flowering of the parent tiller. Early inthe breeding program the initial collections of P~QQnnUQ exhibited a wide range of genetic variation innearly every imaginable trait.

seed of the annual form. The seedlingsbecome established in damaged orweakened open areas of turf, andthrough phenotypic plasticity theyadapt to the given management condi-tions of that particular turf (i.e., mow-ing height, moisture availability, andfertility) .

Foa annua has a unique ability toadjust the height of its flowering culmsso that it is capable of flowering andsetting seed under nearly any mowingheight (i.e., as low as 0.10 inch). Cross-pollination events among annual blue-grass parents produce a range of geneti-cally based morphological variation.Turf management programs act aspowerful selection forces. Over time,subsequent generations of Foa annuabegin to take on the characteristics of aperennial form and ultimately adapt tothe particular turf grass managementprogram. Thus, with every generation,Foa annua evolves and adapts in responseto the specific cultivation and manage-ment practices of a given turf.

On old golf course putting greensthis evolutionary process results instrains of highly evolved perennialannual bluegrasses that are becomingknown as greens-type Foa annua.3,6These greens-type Foa annua strains areperennials that possess a short statureand extremely high shoot densities, andare vegetatively aggressive. Seedheadproduction may be a fact of life in any

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future commercial cultivar of greens-type Poa annua. The main problem, cur-rently, is not the production of seed-heads, but rather the lack of any seedsupply of an improved Poa annua forgolf green use.

Greens-type Poa annua may begin toappear on golf greens as young as 10years old. Such a rapid evolutionaryevent is an indication of the extremeselection forces existing on golf greens(primarily mowing height and wear).The selection pressures of the greenenvironment are so intense that ongreens as young as 60 years old, it iscommon to observe a special type ofPoa annua known as dihaploids. Dihap-loids occasionally produce a flowerstalk, but they are absolutely seed sterileand thus exist entirely as vegetativeperennials. Such dihaploids representsome of the densest, finest, and highest-quality turf strains yet observed. 8

REALIZING THE POTENTIALOver the years and throughout theworld, turf grass scientists and geneticistshave described the potential to breedimproved strains of Poa annua for thegolf industry.4,10This is due to the highturf quality and the enormous amountof morphological variation present inthe perennial forms of Poa annua. How-ever, the main obstacles that need to beovercome for the successful cultivationof Poa annua seed for the commercial

market are 1) low seed yield, 2) theindeterminacy of seed maturity, and 3)the control of undesirable forms of Poaannua within seed production fields.

Overcoming the first two obstacleshas heen among the goals of the PennState breeding program, with limitedsuccess to date. Overcoming the thirdobstacle through reliance on chemicalcontrol may only delay the problem, asseveral herbicide-resistant strains havebeen reported among plants of theannual form?,9 We have thus beenresearching production practices (i.e.,rotating seed production fields on anannual cycle) that will reduce thisobstacle to an acceptable level.

Without doubt, the cultivars ofperennial greens-type Poa annua willhave their share of unforeseen problems,and our breeding program will continueits search for genetic solutions. Ourfocus is to develop commercial seedsupplies for golf courses that have orwould like to have annual bluegrassgreens. Currently, golf courses that haveannual bluegrass greens do not have anadequate seed source for use in routinemaintenance, renovations, or new con-struction. The ulimate goal of PennState's greens-type Poa annua breedingprogram is not to replace creepingbentgrass as a golf green putting grass,but rather to offer an alternative forsituations where annual bluegrass issimply a better choice.

Editor's Note: More about this researchand other USGA-funded researchprojects can be found on the USGA'sTurfgrass and Environmental ResearchOnline at: http://usgatero.msu.edu.

REFERENCES1. Beard,]. B. 1970. An ecological study ofannual bluegrass. USGA Green Section Record8(2):13-18.

2. Breuninger,]. 1993. Poa annua control in bent-grass greens. Golf Course Management 61 (8):68-73.

3. Dionne,].,Y Castonguay, P. Nadeau, and YDesjardins. 2001. Freezing tolerance and carbo-hydrate changes during cold acclimation ofgreen-type annual bluegrass (Poa annua 1.)ecotypes. Crop Science 41:443-451.4. Duff, 0. T. 1978. Disagreement arises overvariant of annual bluegrass. University ifRhodeIsland Tuifgrass Research Review 3:1-3.5. Hanson, B. D., and C.A. Smith. 2000. Diuron-resistant Poa annua is resistant to norflurazon.VVCedSci. 48:666-668.6. Huff, 0. 1996. Poa annua for golf coursegreens. Gounds Maintenance January, pp. G2-G 10.

7. Huff, 0. 1998. The case for Poa annua ongolf course greens. Golf Course Management66(10) :54-56.

8. Huff, 0. 1999. For richer, for Poa. USGAGreen Section Record 37(1):11-14.9. Kelly, St. T., G. E. Coats, and D. S. Luthe. 1999.Mode of resistance of triazine-resistant annualbluegrass (Poa annua). VVCedTechnology13:747-752.10. Law, R. 1977. The turf grass potential of Poaannua ecotypes.Journal ifSports Tuif ResearchInstitute 53:117.11. Law, R.,A. 0. Bradshaw, and P. 0. Putwain.1977. Life-history variation of Poa annua.Evolution 31:233-246.12. McCarty, B. 1999. Controlling Poa annuain bentgrass greens. Grounds Maintenance34(5):17-20.

13. McNeilly, T. 1981. Ecotypic differentiationin Poa annua: interpopulation differences inresponse to competition and cutting. NewPhytologist 88:539-547.

14. Piper, C.V, and R.A. Oakley. 1927. Annualbluegrass (Poa annua). Bulletin if the USGA GreenSection 7 (7): 128-129.

15.Vermeulen, P. 1989. Consider Poa annua foryour new green. USGA Green Section Record27(5):17.

16. Warwick, S. 1. 1979. The biology of Canadianweeds. 37. Poa annua 1. Canadian Journal ifPlantScience 59: 1053-1066.

17.Zontek, S.]. 1973.A positive approach to Poaannua management. USGA Green Section Record11(2):1-5.

DAVIDR. HUFF,PH.D., is an associateprqftssor if tuifgrass breeding and genetics atthe Pennsylvania State University.

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