Competitive Ability and Phytotoxic Potential of Four WInter Canola Hybrids as Affected by Nitrogen Supply

8/3/2019 Competitive Ability and Phytotoxic Potential of Four WInter Canola Hybrids as Affected by Nitrogen Supply

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RRch

W (Brassica napus L.), or oilseed rape, habecome an important economic crop in many areas world-wide, and it is usually cultivated in a crop rotation that includeswinter cereals (Rathke et al., 2005; Brennan and Bolland, 2007Hanson et al., 2008). Canola seed yield and oil content are closely

related to available N (ferti lizer plus soil NO3N) ( Jackson, 2000).Compared with cereals, winter canola requires a higher amountof nutrients, and available nitrogen frequently limits seed yieldColnenne et al. (1998) reported that canola has higher critical Ndemand for biomass formation than wheat.

Successful weed management is essential to canola produc-tion (Martin et al., 2001), and cultivars with characteristics thatprovide great competitive ability (time to emergence, biomassaccumulation, or plant height) might be the best choice to sup-press weed growth and interference (Beckie et al., 2008). How-ever, a wide variation in competitive ability against weeds existsamong canola cultivars (Beckie et al., 2008). Canola hybrids havebeen introduced as a possible means of increasing yield due to het-erosis (Diepenbrock, 2000) and their greater competitive ability

Competitive Ability and Phytotoxic Potential o Four

Winter Canola Hybrids as Afected by Nitrogen Supply

Ioannis Vasilakoglou,* Kico Dhima, Nikitas Karagiannidis, Thomas Gatsis, and Konstantinos Petrotos

BTRcT

Lowinputsinnitrogenmayaffectcanola(Bras-

sica napusL.)competitivenessandallelopathic

potential aswell asgrain and oil yields.A 2-yr

studywasconductedtoassessnitrogensupply

effectontheabilityoffourcanolahybridstocom-

petewithcornpoppy(Papaver rhoeasL.)aswell

asitseffectoncanolaseedandoilyields.Phyto-

toxicpotentialofcanolahybridsongermination

andgrowthofwinterwildoat(Avena sterilisspp.

ludoviciana L.), corn poppy, and wild mustard

(Sinapis arvensisL.)wasalsodeterminedusinga

perlite-basedbioassay.Atcanolablossom,corn

poppy plant number in nitrogen-treated plots

was23%lessthanthatinthenitrogen-untreated

ones.Canolaseedandoilyieldwasreduced18.6

and23.7%, respectively, bythecompetitionof100cornpoppyplantsm2,withElanandTitan

the most productive hybrids. Nitrogen supply

didnotincreaseinallcasesthecompetitiveabil-

ityortheseedandoilyields.Inthelaboratory,

germinationofthewinterweedswascompletely

inhibitedbythegreatestextractconcentration(5

g100mL1)ofallhybrids.Nitrogensupplydidnot

affect,inmostcases,thephytotoxicityofcanola

hybrids,whilephytotoxicitydidnotsignicantly

differamong hybrids.Conclusively, thehybrids

ElanandTitan,cultivatedwithoutanyherbicide

ornitrogenfertilizer,couldbeviableasashort-

termalternativecropsystemforcanolaseedandoilproduction,especiallyinorganicorlow-input

eldsinfestedbycornpoppy.

I. Vasilakoglou, Dep. of Plant Production, Technological and Educa-tional Institute of Larissa, 411 10 Larissa, Greece; K. Dhima, N. Kara-giannidis, and Th. Gatsis, Dep. of Plant Production, Technological andEducational Institute of Thessaloniki, 574 00 Echedoros, Greece; KPetrotos, Dep. of Biosystems Engineering, Technological and Educa-

tional Institute of Larissa, 411 10 Larissa, Greece. Received 20 May2009. *Corresponding author ([email protected]).

Abbreviations: AC, ability to compete; AWC, ability to withstandcompetition; HB, Harper and Berkenkamp growth stage; Y, quantum

yield of photosystem II.

Published in Crop Sci. 50:111 (2010).doi: 10.2135/cropsci2009.05.0270Published online DATE. Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA

All rights reserved. No part of this periodica l may be reproduced or transmit ted in anyform or by any means, electronic or mechanical, including photocopying, recording,or any information storage and retrieval system, without permission in writing fromthe publisher. Permission for printing and for reprinting the materia l contained hereinhas been obtained by the publisher.


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2 www.crops.org cropscience, vol. 50, mayjune2010

compared with the open-pollinated cultivars (Zand andBeckie, 2002).

Allelopathy is also a major component of weed-cropinterference, and it could be supplementary to integratedweed management (Kim and Shin, 2003). All species ofthe genus Brassica contain glycosinolates, which are notphytotoxic substances but they break down to isothio-cyanates or thiocyanates (Fenwick et al., 1989). Isothio-

cyanates are likely to contribute to the allelopathic eectsobserved with decomposing Brassica tissues (Al-Khatib etal., 1997). Many isothiocyanates and thiocyanates havealso been reported as strong inhibitors of seed germina-tion and plant growth (Ju et al., 1983; Dale, 1986; Teas-dale and Taylorson, 1986; Bialy et al., 1990).

Corn poppy (Papaver rhoeas L.) is an annual herbaceousplant up to 90-cm tall, with branched taproot and erect,stiy branched hairy stems (Mitich, 2000). It is the mostimportant dicot weed in winter cereals in Greece (Damana-kis, 1983) and other areas of southern Europe that have aMediterranean climate (Torra and Recasens, 2008). Its abil-

ity to invade, grow, and persist in cereal elds could be attrib-uted to the formation of an abundant seed bank, an extendedperiod of germination, and a high seed production (Holm etal., 1997). However, competition between corn poppy andwinter dicot crops has not been well studied.

Despite the fact that canola cultivars with great com-petitive and/or phytotoxic ability could be a useful tool insustainable agriculture systems, they have not been deter-mined suciently. Furthermore, data related to the role ofnitrogen supply on canola competitive ability and its phy-totoxicity on winter weeds are limited. The objectives ofthis research were (i) to assess the eect of nitrogen supply

on the competitive ability against corn poppy as well as onyields of four canola hybrids in the eld and (ii) to inves-tigate inhibitory eects of these hybrids aqueous extractson sterile oat (Avena sterilis spp. ludoviciana L.), corn poppy,and wild mustard (Sinapis arvensis L.), three of the mostimportant winter weeds in Greece (Damanakis, 1983).

MTRIL ND MThOD

Field xperiment

Experimental SiteA eld experiment was conducted in 20052006 (Year 1) and

was repeated in 20062007 (Year 2) at the Technological andEducational Institute Farm of Thessaloniki in northern Greece(224410 E, 403706N). Experiments were established on asandy loam (Typic Xeropsamment) soil whose physicochemicalcharacteristics were sand 644 g kg1, silt 280 g kg1, clay 76 g kg1,organic matter content 10 g kg1, and pH (1:2 H

2O) 7.6. Preplant

soil analysis conducted in the middle of September showed thatinitial nitrate content ranged from 84 to 88 and 89 to 93 mg kg1of soil in Year 1 and Year 2, respectively. Mean monthly tem-perature and rainfall data recorded near the experimental areaare shown in Fig. 1. The experimental area was naturally infestedby 110 to 120 plants m2 of corn poppy (as conrmed by a visual

assessment made during the 20042005 growing season), one ofthe most important winter broadleaf weeds in Greece (Dam-anakis, 1983). Corn poppy density mentioned above was greaterthan that typically observed in Greek canola elds.

Treatments and xperimental DesignFour canola hybrids (Elan, Titan, PR46w31, and PR45w04)were planted by hand in 40-cm rows to achieve an approximatedensity of 63 seeds m2, which reects the common practice in

Greek canola elds. Canola hybrids have recently been intro-duced in Greece to replace open-pollinated cultivars, and thesefour hybrids belong to the most cultivated ones. The plantingdates were 12 Oct. 2005 and 15 Oct. 2006. Two days beforecanola planting, 40 kg P ha1 as superphosphate were broadcast-applied and incorporated into soil of all experimental plots.Carbofuran (2,3-dihydro-2, 2-dimethylbenzofuran-7-ylmethyl-carbamate) was applied at 1.2 kg ha1 at canola planting for gen-eral insect management. In both years, the experimental area wasirrigated two times with a drip irrigation system and a total vol-ume of 60 mm of water. In Year 1, irrigation was applied duringMay, whereas the experimental area was irrigated during April in

Year 2. This was done because of the low rainfall recorded dur-

ing May in Year 1 and April in Year 2 (Fig. 1). The previous cropwas two-row barley (Hordeum vulgareL.), which was harvested inmid-June 2005. Barley straw was baled and removed after har-vest, and barley volunteer plants were observed at very low den-sities during the experiment. Other common cultural practiceswere imposed as needed during the growing season.

A split-split-plot arrangement of treatments was employedin a randomized complete block design with four replicates.Main plots consisted of two nitrogen fertilizer levels (withoutN supply and with 100 kg N ha1 as urea 2 d before planting)with a plot size of 30 5 m. Urea was broadcast-applied andincorporated into the soil, reecting the common practice inGreek canola elds. All main plots were separated by a 3-m wide

alley. Each main plot was divided into four 6 5 m subplots of12 canola rows each. The four canola hybrids were the subplots.All subplots were separated by a 2-m wide alley. Each subplotwas subdivided into two 2.5 5 m areas of six canola rows each,one that remained weed free and one that was infected by cornpoppy. All sub-subplots were separated by a 1-m wide alley andwere left weedy until 15 December, in order for complete cornpoppy emergence. At that time, competition had not started,as canola and corn poppy were at their early growth stages(four- to six-leaf and cotyledon- to four-leaf stage, respectively)(McMullan et al., 1994; Yaghoobi and Siyami, 2008). However,on 15 December of each year, corn poppy was hand removedin half of all sub-subplots (weed-free sub-subplots). In weedysub-subplots, corn poppy uniformly emerged; however, it wasthinned, as needed, to a density of about 100 plants m2 andallowed to grow in competition with canola until harvest.

Data CollectionThe canola stand was counted at 6 wk after planting in the twocentral canola rows of each sub-subplot. Simultaneously, cornpoppy density was measured in a 5 0.8 m area between the twocentral interrows of each sub-subplot. Corn poppy plant numberand fresh weight of both species were determined in a 5 0.4 marea at the middle of the blossom stage of canola at 27 wk after


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Bioassay ProcedureTen canola plants of each hybrid studied in the eld experimenwere randomly harvested from the weed-free sub-subplots atthe middle of blossom growth stage (HB 4.24.3) (Harper andBerkenkamp, 1975) in each year. The harvested plants werechopped into 5-cm-long pieces, dried at room temperature(25C) for 72 h, and ground in a Wiley mill (Thomas ScienticSwedesboro, NJ) through a 1-mm screen. Then, aqueous

extracts (w/v) were prepared in 400-mL glass jars by adding1.25, 2.5, 5.0, or 10.0 g from each plant sample to 200 mLdeionized water and shaking in a horizontal shaker for 4 h a200 rpm. Solutions were ltered through four layers of cheese-cloth to remove ber debris, centrifuged at 1750 g in a cen-trifuge with a 30-cm rotor diameter for 1 h, and supernatantswere then ltered through a layer of lter paper (Whatman No42; W. & R. Balston, Maidstone, Kent, UK). Extracts werestored for 2 to 6 d at 4C until bioassayed. There were threereplicate extracts for each canola hybrid by extract concentra-tion treatment (0.63, 1.25, 2.50, and 5.00 g 100 mL1).

Petri dish bioassays were performed to assess the phyto-toxic eects of the four canola hybrids on winter wild oatcorn poppy, and wi ld mustard. In part icular, germination, roolength, and fresh weight of winter wild oat and wi ld mustard inperlite treated with each of the canola hybrid aqueous extractwere investigated. For corn poppy, only germination was eval-uated because of the small size of its seedlings.

Winter wild oat, corn poppy, and wild mustard seeds (40200, and 50, respectively) were placed in 8.5-cm diameter plasticpetri dishes and were covered with 5 g of perlite. Open petrdishes were moistened with 15 mL of canola extract per petrdish from each of the canola hybrid extracts. Deionized waterwas used in control petri dishes. There were two petri dishes foeach replicate extract, and petri dishes were arranged in a com-

pletely randomized design. Afterward, petri dishes were storedon shallow trays and placed inside a plastic bag to retain moistureTrays were then placed in an illuminated (8 h light:16 h dark)growth chamber at 20 2C for 14 d. At the end of the incu-bation period, plants were removed from petri dishes, carefullywashed free of perlite, and average (mean of the two petri disheused for each replicate extract) germination as well as root lengthand total fresh weight (of the germinated seeds only) were mea-sured. Measured data were expressed as a percentage of the watecontrol. The experimental procedure was conducted twice usingthe canola samples taken in Year 1 and Year 2. Fungal contami-nation was not observed during these experiments.

planting (Harper and Berkenkamp growth stage [HB] 4.24.3)(Harper and Berkenkamp, 1975). During this sampling, one (thefth) of the six canola rows of each sub-subplot as well as the cornpoppy plants found among and around this row (0.40 5 m area)of each weedy sub-subplot were clipped at the surface, and cornpoppy plant density and fresh weight of both species were mea-sured. This stage was chosen because corn poppy had the greatestbiomass and the critical period of competition between canolaand weed had been completed (Martin et al., 2001).

Chlorophyll uorescence and quantum yield of photosys-tem II (Y) were used to assess the reaction of the canola hybridsto nitrogen supply and corn poppy competition. Measure-ments of the chlorophyll uorescence parameters were madeat two canola growth stages (when lower buds were presentbut enclosed by leaves [HB 3.1] and when all viable buds onraceme were open [HB 4.9]) (Harper and Berkenkamp, 1975)using a chlorophyll uorometer (MINI-PAM, MiniaturisedPulse-Amplitude-Modulated photosynthesis yield analyzer,Walz Company, Eeltrich, Germany) with measurement lightintensity of 0.15 mol m2s1, a frequency of 0.6 kHz, and asaturation pulse intensity of 16,000 mol m2s1 for 0.8 s. Twomeasurements per plant were made on the upper leaves of ve

marked plants in the center of each sub-subplot to determineuorescence at steady state (F

s) and the maximum uorescence

after saturation ash (Fm

). Quantum yield of photosystem IIwas calculated using the equation developed by Genty et al.(1989): Y = (F

mF

s)/F

m. The average of the 10 measurements

per sub-subplot was used for further data ana lysis.At harvest, canola seed yield and 1000-seed weight were

determined by hand harvesting the pods of canola plants in two5-m-long rows (the second and third) of each sub-subplot at20 June of both growing seasons. Furthermore, seed yield sam-ples were forced-air dr ied at 29C to a uniform moisture level,cleaned, weighed, and a subsample of 200 g taken for seed oilcontent. Oil concentration was determined using the crude fat

method (Association of Ocial Analytical Chemists, 1990). Oilyield was calculated by multiplying seed yields by the concen-tration of oil in seeds, both corrected to 8% moisture content.

Competition IndicesCompetition indices of canola were calculated according to Wat-son et al. (2006). Ability to withstand competition (AWC) wascalculated as AWC = 100 (Y

wp/Y

wfp), where Y

wpis the seed yield

from the weedy sub-subplot and Ywfp

is the seed yield from theweed-free sub-subplot. Ability to compete (AC) was calculatedas AC = 100 [(b

w/b

t) 100], where b

wis the fresh weight of corn

poppy and btis the total fresh weight (canola and corn poppy).

Laboratory xperiment

Plant MaterialSeeds from mature plants of winter wild oat, corn poppy, andwild mustard were collected near the experimental area dur ing

June 2004. All collected seeds were dried in the greenhouse,air-cleaned to remove unviable seeds and other plant residues,and stored in a refrigerator at 3 to 6C until used for the experi-ment. The viability of winter wild oat, corn poppy, and wildmustard seeds was eva luated before use and was approximately25, 10, and 22%, respectively.

Fig. 1. Total monthly rainfall and mean monthly temperature during

the experiment.


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tatistial nalysesData received from the eld experiment were analyzed over thegrowing season (year). A split-plot factorial approach (nitro-gen supply canola hybrid) was performed for canola and cornpoppy emergence (6 wk after planting), corn poppy plant num-ber, and fresh weight of both species (27 wk after planting) aswell as for AWC and AC data. Corn poppy fresh weight (b

w

for AC) and canola seed yield values (Ywp

for AWC) measuredin individual weedy sub-subplots were used as numerators.However, treatment means for canola fresh weight plus cornpoppy fresh weight mean values from weedy sub-subplots (b

t

for AC) and canola yield from weed-free sub-subplots (Ywfp forAWC) were used as denominators to improve normality andhomogeneity of data var iances. Corn poppy plant number andfresh weight data before the ANOVA were square-root(x)- andlog(x)-transformed, respectively, to reduce their heterogeneity,but means presented are back-transformed values. Canola data(quantum yield of photosystem II [Y], fresh weight [27 wk afterplanting], seed yield, oil yield, and 1000-seed weight) wereanalyzed by using a split-split-plot factorial approach (nitrogensupply canola hybrid corn poppy competition).

Winter weed bioassay data were analyzed over repeti-tion time using a factorial approach (nitrogen supply canolahybrid aqueous extract concentration). Data for the germina-tion, root length, and total fresh weight of the three weed spe-cies before the ANOVA were log(x + 1) transformed to reducetheir heterogeneity, but means presented are back-transformedvalues. Linear, quadratic, hyperbolic, exponential, and loga-rithmic equations were tested for their suitability to describethe relationship between weed germination, root length, andtotal fresh weight response and canola aqueous extract concen-tration. The equation with the highest adjusted coecient ofdetermination (R

a2) and Fvalues was judged to be the most

appropriate. In these regression equations, germination, rootlength, and total fresh weight (% of control) were the dependent

variables (y), while canola aqueous extract concentration (g dryweight 100 mL1) was the independent variable (x). Also, thephytotoxic doseresponse eects of canola extracts on winterweeds germination, root length, and fresh weight were assessedby the Whole-range assessment method (An et al., 2005). Inhi-bition index was calculated by Eq. [1] used by Liu et al. (2007).

I=Dc

Dn[R(0)f(D)]dD/0DnR(0)dD [1]

In this equation, concentrations tested ranged f rom 0 to Dn, D

c

was the threshold dose at which response equaled the va lue of

control and above which the responses were inhibitory, R(0)was the response at 0 g dry matter per 100 mL (control), and

f(D) represented the response function. Germination, rootlength, and total fresh weight inhibition areas across the wholerange of canola hybrids extract concentrations and the corre-sponding Inhibition indices (I) were calculated separately foreach replicate using the WESIA (Whole-Range Evaluation ofthe Strength of Inhibition in Allelopathic-Bioassay) software(Liu et al., 2007) and afterward were subjected to a combinedover repetition time ANOVA.

The programs SPSS (SPSS, 1997) and MSTAT (MSTAT-C, 1988) were used to conduct regression analyses and analyses

of variance, respectively. Fishers protected LSD procedures wereused to detect and separate mean treatment dierences at P= 0.05.

RULT ND DIcUION

Field xperimentInitial nitrate content, which was greater than that typi-cally observed during the growing season in Greek elds,could be the result of the very low rainfall recorded duringsummer (Fig. 1) and, consequently, of the restricted leach-ing of nitrate form during this period. However, only partof this nitrogen amount could be used by canola, mainlybecause of nitrate leaching and denitrication during

winter (Colnenne et al., 2002; Sieling et al., 2006).

Weed Response

Corn poppy emergence at 6 wk after planting was notsignicantly aected by year, nitrogen supply, and canolahybrid. In particular, corn poppy density averaged 104plants m2 (data not shown). Similarly, Beckie et al.(2008) found that open-pollinated and hybrid canolahad no signicant eect on total weed seedling densityat 4 wk after crop emergence. However, at crop blossom(27 wk after planting), dierential corn poppy suppres-sive ability among canola hybrids was evident, agreeingwith Beckie et al. (2008). In particular, corn poppy plantnumber was aected by year, nitrogen supply, and canolahybrid, whereas corn poppy fresh weight was aectedonly by canola hybrid (Table 1). So, the means presentedin Table 2 are averaged across year and nitrogen supply,while the nitrogen supply eect on corn poppy plant num-ber is discussed. At 27 wk after planting, corn poppy plantnumber in nitrogen-treated plots was 23% less (89 plantsm2) than that in nitrogen-untreated ones (116 plants m2).The lower corn poppy plant number in nitrogen-treated

Table 1. Signicance levels for corn poppy (Papaver rhoeas

L.) plant number or fresh weight data (27 wk after planting) as

well as ability to withstand competition (AWC) and ability to

compete (AC) data of four winter canola (Brassica napus L.)

hybrids in 20052006 (Year 1) and 20062007 (Year 2).

Source

df

Signicance of Fratio

Plant number Fresh weight AWC AC

Years (Y) 1 * ns *** ns

Replicates (Y) 6 ns ns * ns

Nitrogen (N) 1 * ns ** ns

N 1 ns ns * *

Error 6

Canola hybrid (CH) 3 ** * ns ns

Y CH 3 ns ns * ns

N CH 3 ns ns ns ns

Y N CH 3 ns ns ns ns

Error 36

CV, % 11.8 8.1 18.0 15.5

*Signicant at the 0.05 level.

**Signicant at the 0.01 level.

***Signicant at the 0.001 level.Corn poppy plant number and fresh weight data before the ANOVA were sqrt(x) or

log(x) transformed, respectively.

ns, not signicant.


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plots, as compared with that in nitrogen-untreated ones,could be attributed to the greater soil nitrogen concentra-tion in nitrogen-treated plots, which, associated with theextended canola root system, should result in greater nitro-gen use by canola hybrids and, consequently, in greaterearly canola growth (Colnenne et al., 2002). The lowercorn poppy plant number and fresh weight recorded inthe hybrid PR46w31, as compared with those recorded in

the hybrids Elan and PR45w04 (Table 2), could be attrib-uted to greater nitrogen use eciency at vegetative stage,resulting in dierent growth rates among canola hybrids(Svecnjak and Rengel, 2006).

Canola Response

Canola emergence at 6 wk after planting was not sig-nicantly aected by year, nitrogen supply, and canolahybrid. In particular, canola density averaged 60 plantsm2 (data not shown). The AWC of canola was aectedby year and nitrogen supply, as well as by year nitro-gen supply and year canola hybrid interactions (Table

1). However, the AC of canola was aected only by yearnitrogen supply interact ion. In Year 1, AWC did not dif-fer between nitrogen supply treatments and among canolahybrids (ranged from 75.9 to 78.4%). However, in Year2, AWC in nitrogen-treated plots was greater than thatin nitrogen-untreated ones (97.1 and 85.8%, respect ively).Safahani Langeroudi and Kamkar (2009) found that win-ter canola AWC of wild mustard ranged from 4 to 47%.In Year 1, AC was greater in nitrogen-treated plots, ascompared with the nitrogen-untreated ones (81.2 and65.1%, respectively), whereas it was not aected by nitro-gen supply in Year 2 (ranged from 72.2 to 75.5%). The

lack of dierence between AC values in nitrogen-treatedand nitrogen-untreated plots in Year 2 could be attributedto low rainfall recorded during January to April (Fig. 1),which may have resulted in lower nitrogen utilization e-ciency and lower canola early growth rate, as comparedwith Year 1. The greatest AWC value was provided by thehybrid Elan. Generally, nitrogen supply did not improvethe competitive ability of all canola hybrids and for eachhybrid in both years, perhaps because of the satisfactoryinitial nitrate content in soil and the dierent nitrogenutilization eciency among hybrids.

At HB 3.1 (before blossom) canola growth stage, quan-tum yield of photosystem II (Y) was not aected by year,nitrogen supply, canola hybrid, and corn poppy competition.However, at HB 4.9 (end of blossom) canola growth stage,the Y was aected by year (P< 0.01), canola hybrid (P

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Competitive Ability and Phytotoxic Potential of Four WInter Canola Hybrids as Affected by Nitrogen Supply