Salts Influence Nematodesin Seashore PaspalumAre seashore paspalum roots affected by plant-parasiticnematodes under high-salinity irrigation?BY ADAM C. HIXSON, TODD LOWE, AND WILLIAM T. CROW

Figure IEffects of sting nematode (Belonolaimus longicaudatus) on total root lengths

of Sealsle I seashore paspalum compared to Tifdwari bermudagrass.Total root lengths are the combined lengths of all roots present

in a soil core taken from experimental pots, not actual root depth.

2002 2003Seashore Paspalum

todes. Sting nematodes are ecto-para-sites that live outside plant roots anddamage lateral roots as soon as they areformed. Lance nematodes are migratoryendo-parasites that enter turfgrass rootsand cause damage by feeding as well asphysically tunneling through cell walls.Ultimately, plant-parasitic nematodesdecrease root growth and the plant's

Year

100• Inoculated

90• Uninoculated

80..-.en 70G).s:us::~ 60.s:~t).()s:: 50G)..J~00 40a::ra~ 30~

20

10

02002 2003

Bermudagrass

A major limitation of growingturf grass in sandy soils throughout thesoutheastern U.S. is the destruction ofroots by plant-parasitic nematodes.There are several types of plant-para-sitic nematodes, but the most injuriousnematodes throughout the southeasternU.S. are sting (Belonolaimus longicaudatus)and lance (Hoplolaimus galeatus) nema-

Seashore paspalum can quickly spread in salineconditions as long as proper nutrients and soilconditions are present.

Water quality is an ever-increasing issue on golfcourses as the demand for

potable water increases and alternativewater sources are utilized for golfcourse irrigation. In fact, recycled wateras the primary source of irrigation hasincreased for Florida golf courses from8% in 1974 to nearly 50% in 2000.3

As a result, salt-tolerant turf grasses arebecoming necessary in many areas be-cause of groundwater use restrictions,salt accumulation in soil, and saltwaterintrusion into groundwater. Seashorepaspalum (Paspalum vaginatum) is awarm-season turf grass adapted for salineconditions and has been utilized onsalt-affected sites for the past 30 years.Breeding efforts over the past decadehave provided several varieties withimproved leaf texture, color, and overallquality, and its use on golf coursesthroughout Florida and the coastalsoutheastern U.S. is increasing.

JANUARY-FEBRUARY 2005 9

Figure 2Effects of lance nematode (Hoplolaimus galeatus) on total root lengthsof Sealsle I seashore paspalum compared to Tifdwarf bermudagrass.

Total root lengths are the combined lengths of all roots presentin a soil core taken from experimental pots, not actual root depth.

ability to take up water and nutrients.Aboveground symptoms of plant para-sitic nematode damage become evidentin the form of sporadic turf thinningand chlorosis.

Sting and lance nematodes aredestructive pests on a variety of turf-grasses, but little is known about theirdamage to seashore paspalum. Seashorepaspalum has only recently been deter-mined to be susceptible to sting nema-todes, while the effects of lance nema-todes on seashore paspalum root healthremain unclear (Figures 1 and 2). Main-taining acceptable turfgrass quality isincreasingly difficult when the manageris forced to reduce water consumptionor switch to alternative water sources .An additional unknown aspect is theeffect of salinity levels on sting andlance nematode populations in seashorepaspalum. Plant-parasitic nematodes areprimarily aquatic animals residing infIlms of water surrounding soil particles.The premise of this research is toinvestigate if disruptions in this habitat,such as saline irrigation, can affect bio-logical processes and possibly decreasenematode populations.2002 2003

Seashore PaspalumYear

2002 2003Bermudagrass

100• Inoculated

90• Uninoculated

80.-.en 70Q).cucC 60.c~1)0c SOQ)...I~00 40~"i~ 30~

20

10

0

1,-/

Lance nematodes are able to enter seashore paspalum roots,causing damage to the root cortex.

GREENHOUSE TRIALSExperiments were performed to estab-lish relationships between increasingirrigation salinity levels and populationlevels of sting nematodes and lancenematodes. Greenhouse experimentswere conducted in 2002 from April toSeptember and repeated in the springand summer of 2003 at the Universityof Florida Turfgrass Envirotron researchfacility in Gainesville, Florida.

Nematode-free plugs of Sealsle 1seashore paspalum were planted into6-inch clay pots filled with 100%USGA specifIcation sand in a climate-controlled greenhouse. Sting and lancenematodes were then inoculated intothe clay pots and exposed to salinityirrigation levels ranging from 3,200 to35,200 total dissolved salts (TDS) anddeionized water (0 TDS) to serve as acontrol. Nematode population densities

10 GREEN SECTION RECORD

Plant parasiticnematodes significantlyreduce bermudagrassroot growth. reducingthe turf's ability to takeup nutrients and water.

Figure 3Relationship between log transformation of final population densities (PI)

of lance nematodes (Hoplolaimus galeatus) (nematodes 100 cm-3 of soil) (Y)and salinity treatment (x) in 2002 and 2003 greenhouse experiments.

4

5,000 10,000 15,000

Total Dissolved Salts (ppm)

were evaluated 120 days after salinityirrigation treatments began.

In 2003, root length analysis was per-formed in addition to the nematodepopulation measurements. Stained rootsamples were placed into a glass-bottomtray and scanned using a desktop scan-ner to create a black-and-white bitmapimage of the roots. The GSRoot(Louisiana State University, BatonRouge, Louisiana) software programwas used to analyze the bitmap images.This program measures root lengths andsurface areas from scanned images. Rootlength data were recorded for sevenroot diameter ranges, and the resultingvalues were summed to determine thetotal root length of each root sample.

RESULTSANDDISCUSSIONIn both years of the study, reproductionof sting and lance nematodes wasaffected by increasing salinity levels(Figures 3 and 4). Lance nematodepopulations decreased linearly withincreasing salinity irrigation treatments(Figure 3). Lower salinity treatments, 0

~Q. 3

o

DOoCoco.,p.!:J 2c.f.-;cu:t).()o.J

oo

~2002Y = -0.07x + 2.34

r2 = 0.92

-<>- 2003Y = -0.05x + 2.82

r2 = 0.83

20,000

JANUARY-FEBRUARY 2005 II

20,000

at higher salinity treatments probablyoccurred early in the experiment,before the salinity was able to build upin the soil. These results indicate thatthe ability of sting nematodes to stuntroot growth decreased as salinity levels

increased above 9,600 TDS.Moderate- to high- In 2002, repeated

salinity irrigation had applications of high-an impact on sting salinity irrigation (25,600

and lance nematode and 35,200 TDS) caused. nearly complete mortality

reproduction. for both nematodes, but theshoot growth of the grass was stunted

and yellowed. Even though sting andlance nematodes were effectively con-trolled, the turf grass was visually un-acceptable. Seashore paspalum can beirrigated with seawater (34,560 TDS)in the field when soil conditions andincreased irrigation allow for sufficientleaching to occur and turfgrass man-agers fertilize, amend, and cultivate thesoil properly. 1 In the greenhouse, wewere unable to provide sufficient leach-ing, proper amendments, and cultivationof soil necessary for seashore paspalumsurvival at salinity levels near that ofseawater, which may account for thepoor turf grass quality that occurred.

Results from greenhouse experimentsare difficult to extrapolate to field con-ditions, but we can conclude thatmoderate- to high-salinity irrigationhad an impact on sting and lancenematode reproduction. The treatmentsalinity levels were routinely appliedthroughout the experiment; therefore,nematodes did not recover from salinitystress. A discontinuous high-salinityirrigation regime would be moresimilar to irrigation of poor quality ongolf courses where rainfall can leach saltfrom the soil profile.4 Our data suggestthat irrigation with pure seawater orwith seawater as a high percentage ofthe blended irrigation water may havepotential as an effective option forsuppression of sting and lance nema-todes. This information may be vital toturfgrass managers currendy maintainingseashore paspalum known to have anematode problem. Further investigation

-<>- 2003Y = -0.006x2 + O.IOx + 2.38

r2 = 0.78

population in the 9,600 and 12,800TDS treatments, and an abundance ofJ2 at moderate salinity levels resulted inelevated total population numbers(Figure 4). Usually,J2 can be easilyseparated from other lifestages by their darkcolor and stoutbody shape, butJ2 in our studyhad a clear bodycavity, indicatingthey were probablyunable to feed. Root lengthdata in 2003 support this hypothesis,with normal root growth at salinitylevels between 9,600 and 16,000 TDSas opposed to nematode feeding thatoccurred on roots in lower salinitytreatment levels (Figure 5). Reproduc-tion and maturation of the nematodes

5,000 10,000 15,000

Total Dissolved Salts (ppm)

~ 2002Y = -0.007x2 + 0.12x + 1.8

r2 = 0.72

oo

2

3

4

Figure 4Relationship between log transformation of final population densities (Pr)

of sting nematodes (Be/onolaimus longicaudatus) (nematodes 100 em-3 of soil) (Y)and salinity treatment (x) in 2002 and 2003 greenhouse experiments.

to 6,400 TDS, resulted in higher lancenematode reproduction than the highersalinity irrigation treatments (Figure 3).The ability of lance nematodes to enterroots as migratory endoparasites alsodecreased as salinity levels increased.The nematodes were probably not ableto escape the effects of the salinity byentering the roots because the rootcortex tissue does not exclude theelevated ion concentrations associatedwith saline water. Their ability to enterthe roots typically gives them the capa-bility to escape the effects of mostnematicides2; therefore, irrigating withhigh-salinity irrigation may increasenematicide efficacy.

In 2003, second-stage juveniles orJ2 (the life stage of the nematode thathatches from the egg) of sting nema-todes comprised a majority of the

12 GR.EEN SECTION R.ECOR.D

is necessary to determine if frequencyand timing of high-salinity irrigation,in addition to salinity concentration,reduces nematode reproduction andfeeding.

LITERATURE CITED1. Carrow, R. N., and R. R. Duncan. 1998. Salt-affected turf grass sites: assessment and manage-ment. Ann Arbor Press, Chelsea, Michigan.

2. Giblin-Davis, R. M., P. Busey, and B.]. Center.1995. Parasitism of Hoplolaimus galeatus ondiploid and polyploid St. Augustinegrasses .Journal ifNematology 27:472-477.3. Haydu,].]., and A. W Hodges. 2002 .Economic impacts of the Florida golf courseindustry. Institute of Food and AgriculturalSciences, Gainesville, Florida: University ofFlorida.

4. Mashela, P., L. W Duncan,]. H. Graham,and R. McSorley. 1992. Leaching soluble saltsincreases population densities of Fylenchulussemipenetrans.Journal of Nematology 24: 103-108.

ADAM HIXSON is a Ph.D. candidate atNorth Carolina State University in Raleigh(and former Florida Region Green Sectionintern); TODD LOWE is an agronomist forthe Green Sectioni Florida Region; andDR. BILLY CROW is an assistant professorof nematology at the University of Florida inGainesville.

Figure 5Effects of sting nematodes (Be/onolaimus longicaudatus) and salinity levelon root length of Sealsle I seashore paspalum (Paspalum vaginatum).Total root lengths are the combined lengths of all roots present in a

soil core taken from experimental pots, not actual root depth.

140

• Inoculated

**120 • Uninoculated

**.-.(I)

CU 100..c:::uc'=-'.c 80~t).OCCU

.oJ~ 6000a::fa 40~~

20

00 3,200 6,400 9,600 12,800 16,000

Total Dissolved Salts (ppm)* * Indicates a statistical difference from inoculated

Plant-parasiticnematodes feed onbermudagrass roots,

. causing irregularchlorotic anddrought-likepatches.

JANUARY-FEBRUARY 2005 13