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Differential Kochia (Kochia scoparia) Populations Response to GlyphosateAuthor(s): Jason Waite, Curtis R. Thompson, Dallas E. Peterson, Randall S. Currie, Brian L. S. Olson,Phillip W. Stahlman, and Kassim Al-KhatibSource: Weed Science, 61(2):193-200. 2013.Published By: Weed Science Society of AmericaDOI: http://dx.doi.org/10.1614/WS-D-12-00101.1URL: http://www.bioone.org/doi/full/10.1614/WS-D-12-00101.1

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Differential Kochia (Kochia scoparia) Populations Response to Glyphosate

Jason Waite, Curtis R. Thompson, Dallas E. Peterson, Randall S. Currie, Brian L. S. Olson, Phillip W. Stahlman, andKassim Al-Khatib*

Kochia is a troublesome weed throughout the western United States. Although glyphosate effectively controls kochia, poorcontrol was observed in several no-till fields in Kansas. The objectives of this research were to evaluate kochia populationsresponse to glyphosate and examine the mechanism that causes differential response to glyphosate. Glyphosate was appliedat 0, 54, 109, 218, 435, 870, 1305, 1740, 3480, and 5220 g ae ha21 on 10 kochia populations. In general, kochiapopulations differed in their response to glyphosate. At 21 d after treatment, injury from glyphosate applied at 870 g ha21

range from 4 to 91%. In addition, glyphosate rate required to cause 50% visible injury (GR50) ranged from 470 to2149 g ha21. Differences in glyphosate absorption and translocation and kochia mineral content were not sufficient toexplain differential kochia response to glyphosate.Nomenclature: Glyphosate; kochia, Kochia scoparia (L.) Schrad.Key words: Herbicide absorption, herbicide resistant crop, herbicide translocation.

Kochia is an invasive broadleaf weed infesting millions ofhectares of cropland and natural areas in the United States andCanada. It is an aggressive warm season annual dicot thatexhibits protogynous flowering and facultative open pollina-tion (Eberlin and Fore 1984); the aggressive growth habit andprolific seed production enable kochia to spread and competewell for light, moisture and nutrients (Milchunas et. al. 1992).At plant maturity an abscission zone develops at the base ofthe stem causing plant disengagement (Zeroni et al. 1978).Thus, these plants tumble driven by the wind and may travellong distances, spreading seeds across the landscape.

Kochia is ranked as one of the most problematic weeds incultivated fields including corn (Zea mays L.), sorghum[Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.),and soybean [Glycine max (L.) Merr]. Kochia presence canlower grain yield and quality as well as hinder mechanicalharvest (Manthey et al. 1996). For example, kochiacompetition from 6 plants m21 reduced sunflower (He-lianthus annus L.) yield by 27% (Durgan et al. 1990), andcompetition from 70 plants m21 of row decreased wheat yieldby 58% and grain sorghum by 38% (Wicks et al. 1994). Corngrain yields decreased 0.33 kg ha21 for each kg ha21 of kochiabiomass produced (Wicks et al. 1993). In addition, whenkochia was allowed to compete with sugarbeet (Beta vulgarisL.) for the full season, yield was reduced to 225 kg ha21

compared to 49,177 kg ha21 when kochia was removed4 weeks after sugarbeet emergence (Weatherspoon andSchweizer 1969).

Tillage is an effective practice to control kochia. With rapidadoption of no-till systems, chemical control has become thepreferable method to control weeds. Kochia emergence,however, was found to increase almost fourfold under no-till compared to tilled systems (Anderson and Nielsen 1996).In addition, in many parts of the western United States,kochia may emerge over an extended period of time from

early spring through late July during which most crops emerge(Weatherspoon and Schweizer 1969).

Several soil-applied herbicides introduced before or atplanting may effectively control kochia (Thompson et al.2010). Under dry soil conditions, however, most soil-appliedherbicides have low efficacy because of lack of moisture toactivate herbicides (Moyer 1987). In many cropping systems,it is common to control kochia before planting by usingPOST nonselective herbicides such as glyphosate (Donald andPrato 1991). It is critical, however, to apply glyphosate earlyin the spring before plants become too large and difficult tokill (Schwinghamer 2008). A previous report showed thattimely glyphosate application provided up to 99% kochiacontrol (Donald and Prato 1991). Because of high efficacyand the decline in glyphosate cost in recent years, growers areextensively using glyphosate to control kochia prior to cropplanting. In addition, repeated glyphosate use in crops hasincreased because of the widespread adoption of glyphosateresistant crops. In many instances, glyphosate was sprayedmore than once during the growing season. However, relianceon herbicides with the same mode of action for extendedperiods can contribute to weed shifts and the selection ofbiotypes with resistance to herbicides (Holt 1992, Wilsonet al. 2007).

While excellent kochia control has been achieved withglyphosate in many fields across Kansas, poor control ofkochia at recommended use rate was observed in several fieldsin western Kansas. The objectives of this research were tostudy kochia population response to glyphosate and toexamine the possible mechanism that causes differentialresponse to glyphosate.

Materials and Methods

Plant Materials. Kochia seed was collected from 10 sites fromdifferent geographical areas across the western United Statesto ensure adequate kochia genetic variability. These popula-tions include: Eden (EDID ), Jerome County (JCID), andMinidoka County (MCID), Idaho; Hays (HAKS), Ingalls(INKS), Norton (NTKS), Moscow (MOKS), and Syracuse(SYKS), Kansas; Irrigated Agriculture Research and ExtensionCenter, WA (IAREC), and Prosser (PRWA), Washington.INKS, NTKS and MOKS plants were suspected to be lesssusceptible to glyphosate because these sites have a history of

DOI: 10.1614/WS-D-12-00101.1* First, second, and third authors: Graduate Research Assistant, Professor, and

Professor, Department of Agronomy, Kansas State University, Manhattan KS66506; fourth author: Associate Professor, Southwest Research Extension Center,Garden City, KS 67846, fifth author: Associate Professor, Northwest AreaExtension Office, Colby KS 67701; sixth author: Professor, Agricultural ResearchCenter, Hays, KS 67601; seventh author: Professor, Plant Sciences Department,University of California, Davis, CA 95616. Corresponding Author E-mail:[email protected]

Weed Science 2013 61:193–200

Waite et al.: Differential kochia response to glyphosate N 193

repeated glyphosate use. In addition, these sites are 300 kmapart and under different cropping systems. The field inIngalls was irrigated and in a soybean/corn/wheat rotationwhereas the field near Moscow was irrigated corn/cotton(Gossypium hirsutum L.)/wheat rotation; the field in Nortonwas in a soybean/wheat rotation under rainfed conditions.The response of remaining kochia populations to glyphosatewas unknown prior to the study.

Kochia seeds were planted in 50 by 35 by 10 cm flats filledwith 11 kg of a soil mix. The soil was sterilized mixture of 1 : 1by volume blend of sand and Morrill loam (fine-loamy, mesicTypic Arguidolls). The soil had 1.0% organic matter and apH of 7.5. Single kochia seedlings were transplanted into0.9 L containers contain the same sterilized soil mixture as thegermination trays. Plants were grown under greenhouseconditions at 28/25 6 2 C day/night temperatures and 16/8 hday/night periods. The supplemental photosynthetic photonflux was 80 mmol m22 s21. Plants were fertilized (Miracle-Growater soluble fertilizer, Scotts Miracle-Gro Products Inc.,Consumer Products Division, Port Washington, NY 11050)weekly with a solution containing 0.40 mg L21 nitrogen,0.34 mg L21 phosphorus, and 0.33 mg L21 potassium.

Dose Response Study. Kochia plants were treated withglyphosate when the plants were 15 to 20 cm in height.Glyphosate was applied at 0, 54, 109, 218, 435, 870, 1305,1740, 3480, and 5220 g ae ha21. All treatments included0.25% (v/v) non-ionic surfactant (Activate Plus, WinfieldSolution, LLC) and 2.0% (w/v) ammonium sulfate. Treatmentswere applied with a bench-type sprayer (Research Track Sprayer,De Vries Manufacturing, RR 1 Box 184, Hollandale, MN56045) calibrated to deliver 190 L ha21 at 138 kPa. Visibleinjury symptoms were monitored daily and injury ratings weredetermined at 21 d after treatment (DAT), based on 0 5 noinjury and 100 5 mortality. Plant heights were measured at21 DAT, then plants were harvested and dry wt determined.

Stage of Growth Study. Kochia populations from INKS,NTKS, EDID, and IAREC sites were selected for this studybecause INKS and NTKS biotypes expressed the leastglyphosate injury whereas EDID and IAREC were the mostsusceptible populations from the dose response study.

Seedlings were treated with glyphosate 21, 28, and 35 d aftertransplanting when plants were 6, 13, and 25 cm tall.Glyphosate was applied at 0, 54, 109, 218, 435, 870, 1305,1740, 3480, and 5220 g ha21 as described in the doseresponse study. Visible injury symptoms were monitored dailyand injury ratings were determined at 21 DAT and were basedon 0 5 no injury and 100 5 mortality.

Calcium and Magnesium Content Study. Plants containingelevated levels of calcium and magnesium could be lesssusceptible to glyphosate because of reduced herbicide activityfrom glyphosate being bound by the divalent cations Ca2+ andMg2+. A study was designed to determine if glyphosatesusceptibility related to calcium or magnesium levels assuggested by Schuster et al. (2007). Kochia seedlings grownfrom seed collected from INKS, JCID, IAREC, and NTKSsites were grown as described in the growth stage study. Plantswere harvested at 6, 13, and 25 cm growth stages as describedby Schuster et al. (2007). Plants were dried at 65 C for 96 h,then ground to a fine powder, and the tissues digested usingperchloric acid (Gieseking et al. 1935). Calcium andmagnesium contents were determined with an inductivelycoupled plasma spectrometer (Plasma Spectrometer, Agilent7500 series ICP-MS, Agilent Technologies, 9780 SouthMeridian Boulevard, Englewood, CO 80112).

Glyphosate Absorption and Translocation Study. INKS,EDID, IAREC and NTKS kochia populations were selectedfor the glyphosate absorption and translocation study becauseof their wide-range response to glyphosate. Uniform 22-cmtall kochia plants were treated with an 870 g ha21 glyphosaterate as described in the dose response study, and immediatelyafter, plants were treated with 14C-glyphosate ([phosphono-methyl-14C]-glyphosate, specific activity 1094 MBq g21)(PerkinElmer Inc, 940 Winter Street, Waltham, Massachu-setts 02451, USA). Two 1-ml droplets containing a total of1333 Bq 14C-glyphosate were applied to the upper surface ofthe middle of the leaf at the eighth node from the bottom ofthe plant. Glyphosate mixture included 0.5% (v/v) crop oilconcentrate (Crop oil concentrate, Crop Oil Plus, a mixtureof paraffinic oil plus emulsifiers, Land O’ Lakes, P.O. Box

Table 1. Glyphosate rate required to cause 50% visible injury (GR50) and 50%dry wt reduction (GD50) for ten kochia populations as affected by glyphosate 21 dafter treatment.

Population

Glyphosate rate

GRa50 GD50

------------------------------------- g ae ha21 ------------------------------------

Ingalls, KS, INKS 2149 2358Norton, KS, NTKS 1566 1696Moscow, KS, MOKS 1322 1818Syracuse, KS, SYKS 687 774Hays, KS, HAKS 678 583Minidoka County, ID, MCID 652 409Prosser, WA, PRWA 600 940Eden, ID, EDID 583 974Prosser, WA, IAREC 583 687Jerome County, ID, JCID 470 548

a GR50 (glyphosate rate required to cause 50% visible injury) and GD50

(glyphosate rate required to cause 50% dry wt reduction) values were calculatedfrom dose response study where glyphosate was applied at 0, 54, 109, 218, 435,870, 1305, 1740, 3480, and 5220 g ae ha21.

Table 2. Glyphosate rate required to cause 50% visible injury (GR50) and 50%dry wt reduction (GD50) 21 d after treatment for most and least glyphosatesusceptible kochia populations at three plant heights.

Population Plant height

Glyphosate rate

GRa50 GD50

cm ------------------------ g ae ha21 ------------------------

Norton, KS, NTKS 6 679 635Ingalls, KS, INKS 6 818 531Eden, ID, EDID 6 348 157Prosser, WA, IAREC 6 218 218Norton, KS, NTKS 15 1288 1583Ingalls, KS, INKS 15 1575 2010Eden, ID, EDID 15 670 774Prosser, WA, IAREC 15 365 748Norton, KS, NTKS 25 1566 2349Ingalls, KS, INKS 25 2279 2445Eden, ID, EDID 25 713 957Prosser, WA, IAREC 25 905 1131

a GR50 (glyphosate rate required to cause 50% visible injury) and GD50

(glyphosate rate required to cause 50% dry wt reduction) values were calculatedfrom dose response study where glyphosate was applied at 0, 54, 109, 218, 435,870, 1305, 1740, 3480, and 5220 g ae/ha21.

194 N Weed Science 61, April–June 2013

64089, St. Paul, MN 55164) to help facilitate droplet contactto the leaf surface (Schuster et al. 2007).

Plants were harvested at 1, 3, and 7 DAT and separatedinto treated leaf, above treated leaf, below treated leaf, androots. Treated leaves were rinsed with 15 ml of deionizedwater for 60 s to remove any unabsorbed glyphosate. Thetreated leaf was then cut into basal, central and distal thirds.Plant sections were oven dried and oxidized (R. J. HarveyBiological Oxidizer, Model OX-600, R. J. Harvey InstrumentCo., 123 Patterson St., Hillsdale, NJ 07642) as described byAl-Khatib et al. (1992). The trapped 14CO2 and radioactivityin the leaf rinsate were quantified by liquid scintillationspectrometry (Tricarb 2100TR Liquid Scintillation Analyzer,Packard Instrument Co., 800 Research Parkway, Meriden,CT 06450). Absorption was calculated by comparing theradioactivity recovered in the entire plant with the totalamount applied. Herbicide translocation was computed as theamount of radioactivity recovered in a given plant part as apercentage of the total radioactivity in the plant.

Experimental Design and Data Analysis. Dose response andstage of growth experiments were conducted as randomizedcomplete block designs. In the dose response, stage of growth

study, calcium and magnesium content, and absorption andtranslocation studies, treatments were replicated 14, 4, 6, and6 times, respectively, and all experiments were conductedtwice. All data were tested for homogeneity of variance,subjected to ANOVA, and pooled when interactions did notoccur. Means were separated by Fischer’s Protected LSD at, 0.05. For the dose response and stage of growth studies,nonlinear regression analysis was used to determine glyphosaterate required to cause 50% visible injury (GR50) and 50% drywt reduction (GD50) as described by Seefeldt et al. (1995).

Results and Discussion

Dose Response Study. In general, glyphosate injurysymptoms were evident in all kochia populations. In addition,kochia injury increased as the rate of glyphosate increased.Glyphosate injury symptoms were general chlorosis, necrosis,and stunting. Symptoms were more severe in JCID, IAREC,MCID, PRWA, EDID, HAKS and SYKS populations wheresymptoms appeared 3 DAT and peaked at 7 to 10 DAT.However, similar but less intense symptoms were evident inINKS, NTKS, and MOKS populations. At rates greater than870 g ha21, glyphosate injury symptoms appeared 5 DAT in

Figure 1. Visible injury ratings 21 d after treatment with glyphosate applied on 6-cm tall plants of four kochia populations. Glyphosate was applied at 0, 54, 109,218, 435, 870, 1305, 1740, 3480, and 5220 g ae ha21. Ingalls, KS (INKS) and Norton, KS (NTKS) populations were the least whereas Eden, ID (EDID) and Prosser,WA (IAREC) were the most glyphosate susceptible populations in the dose response study.


INKS, NTKS, and MOKS populations and slowly progressedthrough the duration of the study. Rates less than 870 g ha21

caused little to no injury on INKS, NTKS, and MOKSpopulations but severe injury to other populations. At 21DAT, glyphosate applied at 870 g ha21 caused 4, 10, 12, 68,69, 77, 78, 79, 82, and 91% injury at NTKS, INKS, MOKS,HAKS, MCID, SYKS, EDID, PRWA, IAREC, and JCIDpopulations, respectively. When glyphosate was applied at2.61 kg ha21, all populations except NTKS and INKS werekilled, these two populations exhibited 82 and 62% injury,respectively (data not shown).

The INKS, NTKS, and MOKS populations had GR50

values of 2149, 1566 and 1322 g ha21, respectively (Table 1).PRWA, EDID, IAREC, and JCID populations exhibitedgreater susceptibility to glyphosate with GR50 values of600, 583, 583, and 470 g ha21, respectively. Three otherpopulations showed an intermediate response. GR50 of dry wt(Table 1) and plant heights (data not shown) of different

kochia populations showed a similar pattern to visible injury.These results are in agreement with the observation in thefields where kochia control was poor at INKS, NTKS, andMOKS. Response of INKS, NTKS, and MOKS populationsto glyphosate is not surprising because these populations werefrom fields that had a previous history of repeated glyphosateuse and producer complaints of poor glyphosate control.Glyphosate was used for a burndown as well as POSTtreatment in glyphosate resistant crops at the INKS, NTKS,and MOKS, while little glyphosate was used on theWashington and Idaho populations.

Stage of Growth Study. Glyphosate injury symptoms weresimilar to the dose response study. In general, glyphosateinjury was more severe in younger plants. Kochia was moretolerant to glyphosate when treated at 25 cm comparedwith either 15 or 6 cm (Table 2). GR50 of EDID andIAREC were 348 and 218 g ha21 at 6 cm growth stage;



670 and 365 g ha21 at 15-cm growth stage; and 713 and905 g ha21 4 at 25-cm growth stage, respectively. INKSpopulation was the least susceptible population toglyphosate at 6-, 15-, and 25-cm growth stages 21 DATwith GR50 values of 818, 1575 and 2279 g ha21, andGD50 values of 531, 2010 and 2445 g ha21, respectively.At the 870 g ha21 rate, however, significant glyphosateinjury was observed at 6-cm growth stage (Figure 1). Ingeneral, IAREC was the most glyphosate susceptiblepopulation at the 6- and 15-cm growth stages, respectively(Figure 1 vs. Figure 2), whereas EDID was the mostglyphosate susceptible population at the 25-cm height(Figure 3). The increased in glyphosate injury in youngerplants is in agreement with the work of others who haveshown that younger common lambsquaters (Chenopodiumalbum L.) plants are more susceptible to glyphosate(Schuster et al. 2007). The decrease in glyphosate injuryat higher rates can be attributed to the ability of moremature plants to tolerate higher glyphosate rates because ofmorphological and anatomical properties such as a thickercuticle, resulting in less herbicide absorption and injury(Wanamarta and Penner 1989).

Higher rates of glyphosate applied at 6 cm growth stagemay provide adequate control of the less glyphosate

susceptible kochia. At the 870 g ha21 glyphosate rate,kochia injury ratings ranged between 60 to 80% in INKS,NTKS, and MOKS populations, whereas at 1305 g ha21

rate all kochia plants were killed (Figure 1). Application ofhigher glyphosate rates on younger kochia may result instronger selection pressure that may result in thedevelopment a higher level of glyphosate resistance (Holt1992).

Calcium and Magnesium Content Study. Calcium andmagnesium contents were similar in all populations withineach growth stage. However, slight differences wereobserved at the 6- and 12-cm growth stages (Figure 4).In addition, calcium and magnesium contents were lowerat the 25-cm growth stage, when plants were leastsusceptible to glyphosate, compared to 6 cm growth stagewhere plants were most susceptible to glyphosate. Further-more, similar calcium and magnesium contents wereobserved in all populations tested. These results differfrom that reported by Schuster et al. (2007) showinghigher calcium content in more developed commonlambsquarters plants that were relatively more tolerant toglyphosate treatment.



Glyphosate Absorption and Translocation Study. Glypho-sate absorption was similar in all populations tested includingthe two most and least glyphosate susceptible population (datanot shown). At 7 DAT, glyphosate absorption was 62%, 70%,65%, and 70% in INKS, IAREC, NTKS, and EDID,respectively. These results disagree with previous researchconducted on other species which showed lower glyphosateabsorption in glyphosate resistant Italian ryegrass that wasattributed to leaf cuticle composition (Nandula et al. 2008).These differences in glyphosate absorption may be attributedto 14C-glyphaste application method. In our study, immedi-ately prior to 14C-glyphosate application plant was treatedwith commercial glyphosate to mimic normal glyphosatetreatment. Nandula et al. (2008), however, applied only 14C-glyphosate without commercial glyphosate treatment prior to14C-glyphosate application to minimize stress during theexposure.

Glyphosate translocation within the leaf (data not shown)and to other plant parts was similar in all kochiapopulations tested (Figure 5). Again, these results do notagree with previous research that showed lower glyphosatetranslocation in resistant horseweed (Conyza canadensis (L.)

Cronq.) (Feng et al. 2004) and rigid ryegrass (Loliumrigidum Gaudin) (Lorraine-Colwill et al. 2001), wherealtered cellular distribution impaired phloem loading andplastid import of glyphosate resulting in reduced overalltranslocation as well as inhibition of 5-enolpyruvylshiki-mate-3-phosphate synthase (EPSPS). However, lack ofdifference in glyphosate absorption and translocation inresistant and susceptible was observed in Palmer amaranth(Culpepper et al. 2006).

This research clearly showed that kochia populations fromIngalls, Norton, and Moscow in Kansas are less susceptible toglyphosate compared to other populations tested. Thisresearch also showed that differences in tolerance toglyphosate among kochia populations do not appear to bethe result of differences in absorption or translocation of theherbicide, or because of differences in cation levels that couldact to sequester glyphosate. Therefore, the cause of toleranceto glyphosate by kochia remains unknown. Further research isneeded to explore other possible mechanisms such as kineticsof the glyphosate target enzyme, EPSPS, including target sitemutation, or over expression of EPSPS in different kochiapopulations.

Figure 4. Calcium and magnesium content of four kochia populations at three plant heights. Ingalls, KS (INKS) and Norton, KS (NTKS) populations were the leastwhereas Jerome County, ID (JCID) and Prosser, WA (IAREC) were the most glyphosate susceptible populations in the dose response study.


Acknowledgments

The authors thank Rick Boydston and Don Morishita for supplyingkochia seeds from Washington and Idaho, respectively. Contributionno. 11–105-J from the Kansas Agricultural Experiment Station.

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Received July 5, 2012, and approved November 14, 2012.


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