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Differential Tolerance of Rice (Oryza sativa) Varieties to ClomazoneAuthor(s): WEI ZHANG, ERIC P. WEBSTER, DAVID C. BLOUIN, and STEVE D. LINSCOMBESource: Weed Technology, 18(1):73-76. 2004.Published By: Weed Science Society of AmericaDOI: http://dx.doi.org/10.1614/WT-03-008URL: http://www.bioone.org/doi/full/10.1614/WT-03-008

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73

Weed Technology. 2004. Volume 18:73–76

Differential Tolerance of Rice (Oryza sativa) Varieties to Clomazone1

WEI ZHANG, ERIC P. WEBSTER, DAVID C. BLOUIN, and STEVE D. LINSCOMBE2

Abstract: Tolerance of nine rice varieties to clomazone at 1.12 kg ai/ha was evaluated from 2000to 2002. Rice injury was 27 to 51% at 14 d after treatment (DAT) and reduced to 5 to 30% at 42DAT with long-grain ‘Drew’ having less injury compared with all medium-grain varieties. Medium-grain ‘Earl’ and ‘LL-401’ were injured most compared with all other varieties at 42 DAT. Plantheight was reduced by clomazone with all varieties except Drew at 34 DAT. Clomazone also reducedplant population of Earl, LL-401, and ‘Wells’, but other varieties were not affected at 34 DAT.However, rice grain yield reduction was only observed with LL-401. These results indicate thatdifferential tolerance to clomazone exists among rice varieties.Nomenclature: Clomazone; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Earl’,‘CL-141’, ‘LL-401’, ‘LL-601’, ‘Wells’.Additional index words: Herbicide tolerance.Abbreviations: DAT, days after treatment; DPRE, delayed preemergence; PPI, preplant incorporated;PRE, preemergence.

INTRODUCTION

Clomazone has recently been labeled for weed controlin southern dry-seeded rice. Although rice has shownacceptable tolerance to clomazone (Mitchell and Gage1999; Mitchell and Hatfield 1996), substantial injury canoccur under various circumstances. Webster et al. (1999)reported 8 to 18% injury with soil-applied clomazone 7d after emergence. Up to 35% rice bleaching was ob-served by Jordan et al. (1998) 2 wk after rice was treatedwith clomazone at 0.56 kg ai/ha and rice maturity delayand yield reduction were found with clomazone at 1.7and 2.2 kg/ha. Bollich et al. (2000) reported 15% or lessrice bleaching when clomazone was applied at 0.28 or0.56 kg/ha with no maturity delay or yield reduction de-tected. Talbert et al. (1999) reported rice bleaching of 3,18, and 60% at 7 d after treatment (DAT) when cloma-zone was applied at 0.45 kg/ha preemergence (PRE), de-layed preemergence (DPRE), and preplant incorporated(PPI), respectively.

In susceptible species, clomazone reduces or preventsaccumulation of plastid pigments, producing plants witha bleached appearance (white, yellow, or pale-green col-ored) (Duke et al. 1991). Selectivity differences betweenclomazone-tolerant and clomazone-susceptible species

1 Received for publication January 6, 2003, and in revised form April 29,2003. Published with the approval of the Director of the Agricultural Exper-iment Station, Louisiana State University AgCenter, Baton Rouge, LA 70803.

2 Researcher and Associate Professor, Department of Agronomy, Professor,Department of Experimental Statistics, Louisiana State University AgCenter,Baton Rouge, LA 70803, and Professor, Rice Research Station, Louisiana StateUniversity AgCenter, Crowley, LA 70527. Corresponding author’s E-mail:ewebster@agctr.lsu.edu.

cannot be accounted for by differential absorption, trans-location, and metabolism (Norman et al. 1990; Vencillet al. 1990; Weston and Barrett 1990); thus differentialsensitivity at the enzymatic site of action may controlspecies selectivity (Scott and Weston 1992).

Rice varieties have displayed differential sensitivitiesto various herbicides. Pantone and Baker (1992) reportedthat long-grain ‘Lemont’ rice was less tolerant to triclo-pyr than medium-grain ‘Mars’ rice or long-grain ‘Te-bonnet’ rice. A study conducted by Zhang and Webster(2002) indicated that long-grain variety ‘Cocodrie’ wasmore tolerant to V-10029 (sodium 2,6-bis[(4,6-dime-thoxypyrimidin-two-yl)oxy]benzoate), an acetolactatesynthase inhibitor (E.C.4.1.3.18), than medium-grain va-riety ‘Bengal’. Currently, there is little published infor-mation available on varietal tolerance of rice to cloma-zone. Such information is important to rice growers andresearchers in terms of making effective use of this her-bicide and reducing potential crop damage and yieldloss. Therefore, the objective of this study was to eval-uate the tolerance of selected rice varieties to clomazone.

MATERIALS AND METHODS

A study was conducted in 2000, 2001, and 2002 atthe Louisiana State University AgCenter Rice ResearchStation near Crowley, LA. Soil was a Crowley silt loam(fine montmorillonitic, thermic Typic Albaqualfs) with apH of 5.5 and 1.2% organic matter. Field preparationeach year consisted of fall disking and two passes in

ZHANG ET AL.: TOLERANCE OF RICE TO CLOMAZONE

74 Volume 18, Issue 1 (January–March) 2004

Table 1. Agronomic characteristics and genetic background of the rice varieties evaluated.a

Variety Grain type Height Tillering

Days to50%

heading100-Seed

weight Pedigreeb

cm d g

BengalEarlLL-401LL-601CocodrieCypressDrewCL-141Wells

MediumMediumMediumMediumLongLongLongLongLong

9710786869491

112112104

MediumLowMediumMediumHighHighLowMediumLow

81717981807680807778

2.782.702.792.772.482.472.162.312.51

Mars//M201/MarsMercury/Rico 1//BengalBengal derivedBengal derivedCypress/L202/TebonnetL202/LemontNewbonnet/KatyMaybelle/93A83510Newbonnet/3/Lebonnet/9902/Labelle

a The data and information were obtained from Steve Linscombe and Xueyan Sha, Louisiana State University AgCenter Rice Research Station, Crowley, LA.b Pedigrees are represented by the parent lines with the orders of crosses indicated by slashes: ‘‘/’’, first cross; ‘‘//’’, second cross; and ‘‘/3/’’, third cross.

opposite directions with a two-way bed conditionerequipped with rolling baskets and S-tine harrows set tooperate at 6-cm depth. The study area was laser-leveledin the winter each year to a slope gradient of 0.2% afterinitial disking. Each rice variety was drill-seeded on May14, 2000, April 17, 2001, and April 15, 2002 at a seedingrate of 112 kg/ha. The plot size was eight 18-cm rowswide and 5 m long.

The experimental design was a randomized completeblock with a two-factor factorial arrangement of treat-ments with four replications. Factor A consisted of ricevarieties, including four medium-grains, Bengal, ‘Earl’,‘LL-401’, and ‘LL-601’ (LL represents glufosinate-re-sistant varieties), and five long-grains, Cocodrie, ‘Cy-press’, ‘Drew’, ‘CL-141’ (imidazolinone-tolerant), and‘Wells’. Agronomic characteristics and genetic back-ground information of the rice varieties are included inTable 1. Factor B consisted of clomazone treatments:clomazone at 1.12 kg ai/ha and no clomazone. Micro-encapsulated clomazone was applied PRE with a CO2-pressurized backpack sprayer calibrated to deliver 143L/ha at 165 kPa.

The entire study was surface irrigated three times be-fore permanent flood establishment; these included: im-mediately after seeding, at the two- to three-leaf ricestage, and at the three- to four-leaf rice stage. The plotarea was treated with propanil at 3.4 kg ai/ha plus mol-inate at 3.4 kg ai/ha plus halosulfuron at 53 g ai/ha 3 dbefore permanent flood establishment to maintain weed-free plots. The permanent flood was established whenrice was at the four- to five-leaf stage. Soil fertility man-agement consisted of 280 kg/ha of 7:21:21 (N–P–K) fer-tilizer preplant and 280 kg/ha of 46:0:0 urea nitrogenimmediately before permanent flood establishment. Stan-dard agronomic and pest management practices were im-

plemented throughout the growing season to maximizeyield.

Visual rice injury (bleaching) was evaluated at 14 and42 d after treatment (DAT) based on a scale of 0 to 100with 0 5 no bleaching and 100 5 complete bleachingor plant death. Plant height was taken at 34 DAT bymeasuring the distance from the ground to the verticallystretched tip of the longest leaf of three plants per plot.Plant population was taken at 34 DAT by counting themain stem numbers in a randomly selected area of 900cm2, which was then converted to plants/m2 for data pre-sentation. Rice was harvested with a small-plot combinefrom the four center rows of each plot to determine grainyield, and rice yield was adjusted to 12% moisture con-tent.

All data were subjected to the Mixed Procedure ofSAS (1999) with year used as a random factor. Type IIIStatistics was used to test all possible effects of fixedfactors (rice variety, clomazone treatment, and rice va-riety by clomazone treatment), and least square meansat 5% probability level (P 5 0.05) were used for meanseparation. Because variety by clomazone treatment in-teraction occurred for rice injury at 14 and 42 DAT, plantheight, and population at 34 DAT, and rice grain yield,tables were made to reflect these interactions, and mean-ingful comparisons were made based on the P values.

RESULTS AND DISCUSSION

Rice Injury. Because visual injury ratings were basedon the nontreated plant of each variety, only injury datawith clomazone were included in the tables (Tables 2and 3). At 14 DAT, injury of LL-401 was 51%, whichwas greater than that of Cocodrie, Drew, CL-141, andWells with P values ranging from 0.0013 to 0.0497 (Ta-

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Volume 18, Issue 1 (January–March) 2004 75

Table 2. Injury of rice varieties by clomazone at 14 d after treatment and P values to compare injury differences between varieties.a,b

Variety Grain type

Varietyc

Earl LL-401 LL-601 Cocodrie Cypress Drew CL-141 Wells Injury

%

BengalEarlLL-401LL-601Cocodrie

MediumMediumMediumMediumLong

NSd NSNS

NSNSNS

NSNS

0.0497NS

NSNSNSNSNS

0.03810.00150.00130.0026

NS

NS0.04970.0436

NSNS

NS0.02180.01880.0333

NS

4350515037

CypressDrewCL-141Wells

LongLongLongLong

0.0381 NSNS

NSNSNS

43273634

a Clomazone was applied at 1.12 kg ai/ha preemergence.b Compare injury means using the P values in the table.c P . ztz.d NS, not significant according to the t test on differences of least square means at P 5 0.05.

Table 3. Injury of rice varieties by clomazone at 42 d after treatment and P values to compare injury differences between varieties.a,b

Variety Grain type

Varietyc

Earl LL-401 LL-601 Cocodrie Cypress Drew CL-141 Wells Injury

%

BengalEarlLL-401LL-601Cocodrie

MediumMediumMediumMediumLong

0.0001 0.0008NS

NSd

0.00080.0043

NS,0.0001,0.0001

0.0242

NS,0.0001

0.0004NSNS

0.0185,0.0001,0.0001

0.0043NS

NS,0.0001,0.0001

NSNS

NS,0.0001,0.0001

NSNS

153028178

CypressDrewCL-141Wells

LongLongLongLong

0.0313 NSNS

NSNSNS

1459

10

a Clomazone was applied at 1.12 kg ai/ha preemergence.b Compare injury means using the P values in the table.c P . ztz.d NS, not significant according to the t test on differences of least square means at P 5 0.05.

ble 2). No injury differences were found between LL-401 and LL-601, Earl, Bengal, or Cypress at P 5 0.05.The long-grain variety Drew was injured 27% with nodifference from Cocodrie, CL-141, or Wells, but the in-jury was less than that of other varieties at P 5 0.05.

At 42 DAT, rice injury with all the varieties declinedcompared with that observed at 14 DAT (Table 3), in-dicating that all varieties were recovering from the initialinjury caused by clomazone. At 42 DAT, Earl and LL-401 were injured 30 and 28%, respectively, which weregreater than any of the other varieties. Drew was injured5%, which was lower than Bengal, Earl, LL-401, LL-601, and Cypress. Based on the injury data, long-grainDrew displayed greater tolerance to clomazone com-pared with Bengal, Earl, LL-401, and LL-601, and Cy-press.

Plant Height, Population, and Grain Yield. At 34DAT, clomazone reduced plant height of all varieties ex-

cept Drew when compared with the nontreated plant (Ta-ble 4). The growth inhibition as reflected by plant heightreduction was probably caused by the interference ofclomazone with chloroplast development and carotenoidand chlorophyll synthesis (Duke et al. 1985). Clomazonealso reduced plant population of Earl, LL-401, and Wellswhen compared with the nontreated plant (Table 5). Be-cause the evaluation of plant population in this studyinvolved only main stem plants, which originated fromseedlings, a reduction in plant population indicated thata portion of the plants died as a result of clomazonetreatment. Even though rice grain yield was numericallyreduced by clomazone with all varieties except Drew,significant yield reduction only occurred with LL-401 atP 5 0.05 when compared with the nontreated plant.

These results indicate that clomazone may injure ricevarieties and result in plant height reduction and standloss, but most varieties have the ability to recover from

ZHANG ET AL.: TOLERANCE OF RICE TO CLOMAZONE

76 Volume 18, Issue 1 (January–March) 2004

Table 4. Rice heights 34 d after clomazone treatment and P values to comparethe height differences between the treated and the nontreated within a varie-ty.a,b

Variety Grain type

Plant height

Treated Nontreated Difference P valuec

cm

BengalEarlLL-401LL-601Cocodrie

MediumMediumMediumMediumLong

2724242324

3232332929

2528292625

,0.0001,0.0001,0.0001,0.0001

0.0017CypressDrewCL-141Wells

LongLongLongLong

22292727

28313232

26232525

,0.0001NSd

,0.0001,0.0001

a Clomazone was applied at 1.12 kg ai/ha preemergence.b Compare height differences between the treated and the nontreated within

a variety using the P values beside them.c P . ztz.dNS, not significant according to the t test on differences of least square

means at P 5 0.05.

Table 5. Rice populations 34 d after clomazone treatment and P values tocompare the height differences between the treated and the nontreated withina variety.a,b

Variety Grain type

Plant population

Treated Nontreated Difference P valuec

main stems/m2

BengalEarlLL-401LL-601Cocodrie

MediumMediumMediumMediumLong

182134158255207

243267292304267

26121332134249260

NSd

0.00010.0001

NSNS

CypressDrewCL-141Wells

LongLongLongLong

255255279231

267279316316

212224237285

NSNSNS

0.028

a Clomazone was applied at 1.12 kg ai/ha preemergence.b Compare height differences between the treated and the nontreated within

a variety using the P values beside them.c P . ztz.d NS, not significant according to the t test on differences of least square

means at P 5 0.05.

the initial injury and maintain their grain yield potentials.However, the results also indicate the existence of dif-ferential tolerance of rice varieties to clomazone. Amongthe rice varieties evaluated, long-grain Drew displayedgreater overall tolerance to clomazone than two medium-grain varieties, Earl and LL-401. The varietal differencein clomazone tolerance is probably not caused by dif-ferential absorption, translocation, and metabolism (Nor-man et al. 1990; Vencill et al. 1990; Weston and Barrett1989). Seed size, which may be related to the survivingability of rice seedlings through nutrient and energy sup-ply, is not a factor caused by the fact that the mediumgrains actually have greater 100-seed weight than thelong grains (Table 1). Because all medium-grain varietiesin this study are Bengal, Bengal-derived, or having Ben-gal as one of the parent lines (Table 1), they probablyinherit the genetic traits that are responsible for theirsensitivity to clomazone from ‘Mars’ or ‘M201’, twoparent lines of Bengal.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Steve Linscombefor providing the rice varieties. Louisiana Rice ResearchBoard provided partial funding for this project.

LITERATURE CITED

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Duke, S. O., R. N. Paul, J. M. Becerril, and J. H. Schmidt. 1991. Clomazonecauses accumulation of sesquiterpenoids in cotton (Gossypium hirsutumL.). Weed Sci. 39:339–346.

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