FiElD SCIENCE

• _

he United States is a land ofimmigrants and so is our mostpopular sports turfgrass,Kentucky bluegrass (Poa praun-sis L.). Kentucky bluegrass is

native to Eurasia and was brought [0 NorthAmerica by the first European settlers as feed

and bedding for their livestock In this warmerclimate, Kentucky bluegrass became natural-ized and like the nation's immigrants,Kentucky bluegrass developed and prosperedin its use as lawns and sports field surfaces.

American-born sports like baseball andfootball began using Kentucky bluegrass for its

beauty and durability under intensive use.Unlike any of our other immigrant cool-seasonrurfgrasses (e.g., perennial ryegrass, tall fescueor bentgrass], Kentucky bluegrass is sod-form-ing and provides superior stability and tractiondue to its production of underground rhizomestems. These rhizomes intertwine and hold the

16 September 2007 www.greenmediaonline.com

FIELD SCIENCEsod together against shearing forces. They also con-tain growing points called nodes where new plantscan begin to develop. Normally new plants form atthe tips of rhizomes as they reach the soil surface.However, a deep vertical mowing can cut rhizomesand stimulate the production of new daughter plantsall along each rhizome. Turf manager RobertHudzik uses this feature at Penn State's BeaverStadium each spring to increase shoot density with-out additional overseedmg.

The aesthetic beauty of Kentucky bluegrass isbeyond compare due to its combination of richgreen color, medium fine texture, and high shootdensity. Its disadvantages include susceptibility todisease and insect pests and a tendency to becomethatchy. Just as the rhizomatous growth habit ofKentucky bluegrass creates a strong sad and stableplaying surface,these same rhizomes also contributeto the addition of organic matter, underneath thegreen leaves, called thatch, If the thatch layerbecomes too thick (>1/2 inch) then playability maybe hindered H.S the sports field becomes too soft.

In addition, the field will lose some of its abilityto grow and recover from damage due to a shal-lower than nonnal root system. However, if there is

too little thatch «1/4 inch), then the field mil lose its ability to absorbthe impact of participants, increasing the risk of injury and/or reducingtraction and the predictability of ball bounce. Properly managing theheight of cut and thatch thickness of Kentucky bluegrass creates someof the highest quality sports field in any venue.

In Europe and Australia, perennial ryegrass is favored overKentucky bluegrass (known in these countries as smooth-meadowgrass) for sports fields. Here in America, Kentucky bluegrass has his-torically been the first choice for sport fields and today is often mixedwith either perennial ryegrass or tall fescue.

During the 1980sand 90s, the component percentage of Kentuckybluegrass seed in high maintenance mixtures began to decrease as sig-nificant genetic improvements were bred into the turf-type perennialryegrasses. In other words, genetic advances in traits like higher shootdensities, darker green color, and shorter stature began to give peren-nial ryegrass a quality that rivaled that of Kentucky bluegrass, and sub-sequently perennial ryegrass use increased in the sports turf market.

During the same time, similar genetic gains were also being realizedin tall fescue. Genetic improvements in Kentucky bluegrass havelagged behind those of either perennial ryegrass or tall fescue for thesimple fact that Kentucky bluegrass does not normally reproduce seedthrough a sexual process. The breeding system of Kentucky bluegrassis known as apomixis, which results in the asexual (without sex) pro-duction of seed. This means that every seed produced is geneticallyidentical to the plant that produced it, or in other words, a genetic car-bon copy of the seed-bearing parent. As such, attempting to bringtogether traits from different parents or improving a trait through arti-ficial selection is nearly impossible. Thus, new types of Kentucky blue-grass only occur when the apomixis system malfunctions and produces

Fill in 135 on reader service form or visit http,/loner<.holim •. com/13973-135

18 September 2007 www.greenmediaonline.com

FIELD SCIENCEan off-type, or an aberrant, progeny.

Most aberrant plants arc quite unaccept-able for turf, however, and so tens of thou-sands of seedling bluegrcsses need to begrown in order that just a few aberrant plantscan be detected that might exhibit potentialimprovements. Once a superior plant hasbeen identified, then the rest of the breedingprocess is comparatively easy becauseapomixis is a great way to preserve the genet-ic makeup of the superior plant and to pro-duce genetically uniform seed. But finding anaberrant plant that exceeds the performanceof any of today's top cultivars is no ea.sy chal-lenge. Nonetheless, the need for improvedcultivars of Kentucky bluegrass remainsstrong because as Dr. C. Reed Funk, RutgersUniversity, would say, ","Vehave a lot of goodculrivars of Kentucky bluegrass, but we don'thave any great ones"

Because of this need for improved blue-grasses, breeders refocused their energiesover the past 15 years and have developed a

Fill in 120 on re~der service form or vi,it http://oners.hotims.com'13973-120

20 September 2007 www.greenmediaonline.com

FIELD SCIENCE

22 September 2007

wide range of new Kentucky bluegrass culti-vars (go to www.ntep.org for the latest list ofculnvers along with their performance ratingsfrom across the country). As a result of theseimprovements and perhaps a regainedappreciation for Kentucky bluegrass's sodforming ability, the percentage component ofKentucky bluegrass in mixtures with perenni-al ryegrass has slowly been increasing overthe past 7-8 years. Sustaining our focus onbreeding improved bluegrasses, we shouldexpect genetics improvements to continue inthe coming years.

No easy taskWhen the time comes, choosing the right

cultivar of Kentucky bluegrass for a specific useis not necessarily an easy task for the scientistor the turf managlOf. Basically, there are typesof Kentucky bluegrasses that perform best dur-ing the spring and fall seasons and other typesthat perform best in the summer months.There are Midwestern common types, mid-Atlantic common types, and then there arethose that nobody has quite figured out whattype they are (the Miscellaneous types).

The types typically preferable for sportsfields are the aggressive types and the com-pact types; however, these types also possessparticular management requirements andmay not be the right choice for everyone.Thus, the selection of which Kentucky blue-grass cultivars to blend together for a sportsfield depends on your application and turf-grass management resources. Since any sin-gle cultivar is only a single individual (geno-type), it is best to blend several cultivarstogether to create some genetic diversity inorder to better combat disease and otherunpredictable stresses.

One of the beautiful features of Kentuckybluegrass as a whole is that. there are a lot ofdifferent types of cultivars to choose from tobest match your needs. Do your research andchoose your cultivars wisely!

Some of the newest breeding efforts withKentucky bluegrass have involved itshybridization with Texas bluegrass (native toNorth America) which has deeper roots,deeper rhizomes, and better heat tolerance,Normally, when two different species arecrossed, the resulting progeny are reproduc-tively sterile. For example, a mule is sterilebecause it is a cross between a donkey and a

horse and the only way to get a mule is tomake the cross. However, the Kentucky/Texas bluegrass hybrids are selected for theirapomitic form of seed reproduction andtherefore entirely avoid this genetic sterilitybarrier. The newest Kentucky/Texas blue-grass hybrids still lack the high turf quality ofpure Kentucky bluegrass culrivars but theyare beginning to make an impressive impactin turf areas reserved for low maintenanceand will only improve in quality as the breed-ing efforts continue.

Maintenance of Kentucky bluegrass canbe much different than the maintenance ofpure tall fescue or perennial ryegrass but nei-ther tall fescue nor perennial ryeb'Tass havethe rhizomatous feature of Kentucky blue-grass (including the so-called "rhizomatoustall fescues"). As budgets allow, the mostimportant management practices to institutefor any sports field are regular mowing, fol-lowed by a nutrition program (fertilization),and finally an irrigation system. When allthree are combined, a very suitable field canbe created. Supplementing these practiceswith core cultivation to alleviate com-paction, vertical mowing to manage thatch,and topdressing and overseeding will onlyenhance the quality, safety, and durability ofmulti-use sports fields,

Kentucky bluegrass management is asmuch an art as a science. For example,Kentucky bluegrass seed is notoriously slowto germinate (10-21 days). Researchers havefound that soaking bluegrass seed overnight(allowing it to drain during the day and repeatthe next night) in their original woven seedbags, using a water-filled garbage can, fol-lowed by air-drying enough to flow through aseed spreader, starts the germination processand greatly enhances its establishment rate.So the next time you need to resurface orbuild a sports field, put Kentucky bluegrasson your list of choices. Although Kentuckybluegrass is an immigrant, its use on sportsfields is as American as apple pie .•

AUTHORS:Dr. David R. Huff is associate professor of tur-

!grass breeding and genetics, at Penn State. Dr.Amhika Chandra is assistant professor of turfgrassbreeding and molecular genetics, Texas A&MUniversity, Dallas. Jeff Borger is an instructor oftuifgrass and weed management at Penn State.

www.greenmediaonline.com