Kakatoch Allelopathic

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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 1, 2012

Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article ISSN 0976 4402

Received on May 2012 Published on July 2012 84

Allelopathic influence of dominant weeds of North-Western Himalayan

region on common cereal crops

Rajan Katoch1

, Anita Singh1

, Neelam Thakur2

1- Department of Crop Improvement, College of Agriculture, CSK Himachal Pradesh Krishi

Vishvavidyalaya, Palampur (H.P.) 176 062 (India)

2- Department of Biosciences,Punjab Agricultural University, Ludhiana, India

[email protected]

doi:10.6088/ijes.2012030131010

ABSTRACT

A study on the allelopathic potential of Ageratum conyzoides and Eupatorium adenophorum

two dominant weeds of North-Western Himalayan region on three common cereals viz.,Triticum aestivum cv. HPW-42 (wheat), Oryza sativa cv. Hasanshrai basmati (paddy) and

Zea mays cv. Girija (maize) revealed significant inhibition of seed germination. Lower

concentration of E. adenophorum macerated aqueous extract showed stimulatory effect on

plumule growth in wheat and maize seedlings while all other treatments led to inhibition of

plumule length. Likewise, the radicle length was significantly more in case of maize

seedlings on exposure to E. adenophorum macerated aqueous extract (50 per cent) than that

of control. All other treatments caused significant reduction in the radicle growth. The

inhibitory effect was much pronounced for radicle growth as compared to the plumule growth

for all the treatments except E. adenophorum macerated aqueous extract (50 per cent). There

was a significant reduction in seed vigor index in case of all the treatments except E.

adenophorum macerated aqueous extract (50 per cent). Among the test crops, maize withlarger seeds was least sensitive to the application of various extracts/fractions while wheat

and paddy with small seeds were more susceptible to the allelopathic effect of both weeds.

The results of the study could be important in planning the area under different crops in view

of the prevalent agro-ecosystem for better outputs.

Keywords: Ageratum conyzoides, Eupatorium adenophorum, wheat, paddy, maize, plant

extracts.

1. Introduction

Allelopathy plays an important role in agro-ecosystems by involving a wide range of plant-plant interaction. Exotic plant species may release certain novel allelopathic chemicals in the

invaded area. Plants native to that habitat may not possess co-evolved defense strategies

against the exotic novel chemicals and may be very susceptible to their inhibitory effects.

This gives the exotic species a competitive advantage over native flora for the successful

establishment in the invaded area (Kanchan and Jayachandra, 1979; Ridenour and Callaway,

2001; Hierro and Callaway, 2003; Bais et al., 2004; Inderjit et al., 2006). The neighboring

vegetation of these weeds indicates that they have some allelopathic potential which might

have been caused either by fallen leaves (through decomposition of leaves) or plant leachates

or root exudates (Putnam and Duke, 1978; Rice, 1984; Inderjit et al., 2006). Consequently,

the release of allelochemicals (organic substances) into the soil inhibits seed germination and

establishment of agricultural crops and vegetation. Weed infestation is one of the majorcauses of yield reduction in crops. The effect of allelopathic chemicals tends to be highly


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Allelopathic influence of dominant weeds of North-Western Himalayan region on common cereal crops

Rajan KatochInternational Journal of Environmental Sciences Volume 3 No.1, 2012

85

species-specific. Ageratum conyzoides and Eupatorium adenophorum are two such exotic

species belonging to family Asteraceae which have successfully invaded a large portion of

North-Western Himalaya region in India. Both are rapidly spreading weeds and are a major

problem for the environmentalists, ecologists and agriculturists. Ageratum conyzoides is an

annual herbaceous tropical plant and has invaded large areas in West Africa, Australia, some

parts of Asia and South America. Eupatorium adenophorum, a native species of tropicalAmerica has also recently drawn worldwide attention for its ever increasing potential to grow

luxuriantly in diverse habitats. It has an edge over other weeds as it is a vigorous perennial

shrub and has colonized cultivated lands, open degraded lands and natural forest.

The present study was carried out to explore the allelopathic potential of E. adenophorum and

A. conyzoides on seed germination and early seedling growth of three cereal crop species,

namely, Triticum aestivum cv. HPW-42 (wheat), Oryza sativa cv. Hasanshrai basmati

(paddy) and Zea mays cv. Girija (maize) under laboratory conditions. Such information

would be beneficial when planning for sowing the agricultural crops near these weeds.

2. Materials and method

2.1 Collection and mechanical processing of plant material

Fresh plant material of E. adenophorum and A. conyzoides was collected from the vicinity of

CSK HPKV, Palampur, India. The collected plant samples were allowed to shade dry. The

dried material was crushed into fine powder using grinder and sieved through mesh of 2mm

pore size.

2.2. Preparation of methanolic extract and aqueous fraction

Finely powdered sample (1 kg) was extracted repeatedly with 50 per cent methanol so as toensure complete extraction of the material. The extract was concentrated initially on rotary

vacuum evaporator and then dried using lyophilizer. Part of crude methanolic extract of each

plant was mixed with water to get a homogenous mixture and subjected to sequential solvent

fractionation with hexane, chloroform, ethyl acetate and n-butanol. The solvent fractions

were not used during the present experiment. The residual aqueous fraction was dried using

lyophilizer. The effect of methanolic extracts and aqueous fractions of A. conyzoides and E.

adenophorum was evaluated at two different concentrations (5 per cent and 10 per cent).

2.3. Preparation of macerated aqueous extract

The fresh plant material of E. adenophorum (500 g) was homogenized using 500 ml water(100 per cent w/v). The aqueous extract was filtered through double-layered muslin cloth.

Portion of it was diluted twice to make the concentration of 50 per cent (w/v). The effect of

macerated aqueous extract of E. adenophorum was investigated at both concentrations (50

per cent and 100 per cent).

2.4. Procurement of seeds of test crops

Seeds of test crops were procured from the Department of Crop Improvement, CSK HPKV,

Palampur. The seeds were surface-sterilized with sodium hypochlorite and used for further

bioassay studies.

2.5. Bioassay studies


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Bioassay studies on seeds of test crops were carried out to study the effect of methanolic

extracts and aqueous fractions of E. adenophorum and A. conyzoides at 5 per cent and 10 per

cent concentrations. The effect of E. adenophorum macerated aqueous extract at 50 per cent

and 100 per cent was also investigated. Crop seeds (10) were placed in 9 cm diameter sterile

Petri plates on two layers of Whatman filter paper No.1. Each Petri plate received 5 ml of the

methanolic extract/aqueous fraction/macerated aqueous extract. For controls, equal volume ofdistilled water was used. The experiment was carried out in triplicate for each treatment and

control. Bioassay studies included the following treatments:

T0: Distilled water

T1a: Eupatorium methanolic extract (5 per cent)

T1b: Eupatorium methanolic extract (10 per cent)

T2a: Eupatorium aqueous extract (5 per cent)

T2b: Eupatorium aqueous extract (10 per cent)

T3a: Ageratum methanolic extract (5 per cent)

T3b: Ageratum methanolic extract (10 per cent)

T4a: Ageratum aqueous extract (5 per cent)

T4b: Ageratum aqueous extract (10 per cent)

T5a: Eupatorium macerated aqueous extract (50 per cent)

T5b: Eupatorium macerated aqueous extract (100 per cent)

The experiment was extended over a period of eight days to allow maximum germination.

The seed was considered germinated when the radicle emerged. Germination counts were

made daily up to eight days. On eighth day, the lengths of plumule and radicle of seedlings

were also recorded. Relative germination ratio and relative elongation ratio of plumule and

radicle were calculated as suggested by Rho and Kil (1986).

Relative germination ratio (RGR)= Germination percentage of test seed x 100

Germination percentage of control seed

Relative elongation ratio [plumule] (RERP)= Mean length of plumule of test plant x 100

Mean length of plumule of control

Relative elongation ratio [root] (RERR) = Mean length of radicle of test plant x 100

Mean length of radicle of control

Seed vigor index (SVI) was calculated according to Abdul-Baki and Anderson (1973) by

multiplying mean germination (%) with mean radicle length (cm).

2.6. Statistical Analysis

Three replications were maintained and completely randomized design was followed for

statistical analysis (Panse and Sukhatme, 1989). The data were subjected to analysis of

variance (ANOVA) at p< 0.05.


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3. Results

3.1 Effect on seed germination

The germination per cent of seeds of all the test crops under the influence of various

treatments is presented in Table 1. The application of different concentration of methanolicextracts and aqueous fractions of both weeds and macerated aqueous extract of E.

adenophorum significantly inhibited the germination of wheat seeds as compared to the

control. The per cent germination of wheat seeds was statistically similar on exposure to

methanolic extracts of E. adenophorum and A. conyzoides at both the concentrations.

However, statistically significant reduction in the per cent germination of wheat seeds was

observed at 10 per cent concentration of aqueous fractions of both weeds as compared to that

at 5 per cent. Likewise, macerated aqueous extract of E. adenophorum (100 per cent)

significantly reduced the per cent germination of wheat seeds as compared to that at 50 per

cent. The maximum RGR (81.44) was observed when the seeds were exposed to E.

adenophorum aqueous fraction (5 per cent) while the minimum (48.11) was in the set with A.

conyzoides aqueous fraction (10 per cent) in case of wheat (Figure 1).

Table 1: Effect of methanolic extracts and aqueous fractions of E. adenophorum and A.

conyzoides and macerated aqueous extract of E. adenophorum on per cent germination of

seeds of test crops (8 days post-application)

Germination (%)S.No. Treatment

Wheat Paddy Maize

1. Water 90.00a 96.70

a 100.00

a

2. E. adenophorum methanolic extract (5 per cent) 63.30bcd

00.00e 96.70

ab

3. E. adenophorum methanolic extract (10 per cent) 56.70cd

00.00e 76.70

de

4.

E. adenophorum aqueous extract (5 per cent) 73.30

b

66.70

c

80.00

cde

5. E. adenophorum aqueous extract (10 per cent) 53.30de

13.30d 76.70

de

6. A. conyzoides methanolic extract (5 per cent) 63.30bcd

63.30c 90.00

abc

7. A. conyzoides methanolic extract (10 per cent) 56.70cd

10.00d 86.70

bcd

8. A. conyzoides aqueous extract (5 per cent) 66.70bc

13.30d 83.30

cde

9. A. conyzoides aqueous extract (10 per cent) 43.30e 00.00

e 50.00

f

10. . adenophorum macerated aqueous extract (50 per cent) 70.00b 93.30

a 90.00

abc

11. . adenophorum macerated aqueous extract (100 per cent) 56.70cd

86.70b 86.70

bcd

GM 63.03 40.30 83.35

F value 12.37 234.90 11.73

S.E. 04.92 03.76 5.50

C.D. at 5% 10.20 07.80 11.41

Data were subjected to analysis of variance (ANOVA) and values followed by same letter(s) within a column

did not differ significantly at p0.05.

A significant reduction in the percent germination of paddy seeds was observed when the

seeds were exposed to various treatments except E. adenophorum macerated aqueous extract

(50 per cent) as compared to the control. Complete inhibition of germination of paddy seeds

was observed when seeds were exposed to E. adenophorum methanolic extract (5 per cent

and 10 per cent) and A. conyzoides aqueous fraction (10 per cent). The reduction in per cent

germination of paddy seeds at higher concentration of each treatment was significantly more

as compared to the corresponding lower concentration. The maximum RGR (96.48) was

found when the seeds were exposed to E. adenophorum macerated aqueous extract (50 percent) in case of paddy (Figure 1).


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0.00

40.00

80.00

120.00

T1 a T1 b T2 a T2 b T3 a T3 b T4 a T4 b T5 a T5 b

Treatments

RelativeGerminationRa

tio

Wheat

Paddy

Maize

Figure 1: Relative germination ratio of seeds of test crops exposed to different

concentrations of Eupatorium adenophorum and Ageratum conyzoides extracts

T1a: Eupatorium methanolic extract (5 per cent); T1b: Eupatorium methanolic extract (10 per cent); T2a:

Eupatorium aqueous extract (5 per cent); T2b: Eupatorium aqueous extract (10 per cent); T3a: Ageratummethanolic extract (5 per cent); T3b: Ageratum methanolic extract (10 per cent); T4a: Ageratum aqueous extract

(5 per cent); T4b: Ageratum aqueous extract (10 per cent); T5a: Eupatorium macerated aqueous extract (50 per

cent); T5b: Eupatorium macerated aqueous extract (100 per cent)

The per cent germination of maize seeds was not significantly reduced by E. adenophorummethanolic extract (5 per cent) and macerated aqueous extract (50 per cent) as compared to

the control. However, E. adenophorum methanolic extract (10 per cent) and macerated

aqueous extract (100 per cent) revealed significant reduction in per cent germination of maize

seeds. Likewise, E. adenophorum aqueous fraction (5 per cent and 10 per cent), A.

conyzoides methanolic extract (10 per cent) and A. conyzoides aqueous fraction (5 per cent

and 10 per cent) significantly reduced the per cent germination of maize seeds as compared to

the control. No significant reduction in per cent germination was observed by A. conyzoides

methanolic extract (5 per cent). The maximum RGR (96.70) was found when the seeds were

exposed to E. adenophorum methanolic extract (5 per cent) while the minimum (50.00) was

in the set with A. conyzoides aqueous fraction (10 per cent) in case of maize (Figure 1).

3.2 Effect on plumule length

A significant stimulatory effect on the length of plumules of wheat and maize seedlings was

observed when seeds were exposed to E. adenophorum macerated aqueous extract (50 per

cent) as compared to the respective controls (Table 2). However, the length of plumules of

wheat and maize seedlings was statistically similar to that of the respective controls when

exposed to E. adenophorum macerated aqueous extract (100 per cent). In all other treatments,

there was a significant reduction in the length of plumules in case of wheat as compared to

the control.

In case of maize, a significant reduction in plumule length was observed on exposure of seedsto E. adenophorum methanolic extract (10 per cent), E. adenophorum aqueous fraction (10


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per cent) and A. conyzoides methanolic extract (10 per cent) as compared to the control. A

significant reduction in plumule length of seedlings of paddy was observed in all the

treatments as compared to the control.

Maximum RER of plumule (151.31) was observed in maize seedlings when exposed to E.

adenophorum macerated aqueous extract (50 per cent) while the minimum (0.0)was in paddyseedlings applied with E. adenophorum methanolic extract (5 per cent and 10 per cent), E.

adenophorum aqueous fraction (10 per cent) and A. conyzoides methanolic extract (10 per

cent) and A. conyzoides aqueous fraction (10 per cent) (Figure 2).

Table 2: Effect of methanolic extracts and aqueous fractions of E. adenophorum and A.

conyzoides and macerated aqueous extract of E. adenophorum on plumule length of test

crops (8 days post-application)

Plumule length (cm)

S.No. Treatment

Wheat Paddy Maize

1. Water 7.97bc

3.53a 2.67

bc

2. E. adenophorum methanolic extract (5 per cent) 3.53e 0.00e 2.50

bcd

3. E. adenophorum methanolic extract (10 per cent) 1.77f 0.00

e 1.23

e

4. E. adenophorum aqueous extract (5 per cent) 7.00cd

0.80c 2.83

b

5. E. adenophorum aqueous extract (10 per cent) 4.33e 0.00

e 2.00

d

6. A. conyzoides methanolic extract (5 per cent) 5.00e 0.87

c 2.27

bcd

7. A. conyzoides methanolic extract (10 per cent) 5.07e 0.00

e 2.17

cd

8. A. conyzoides aqueous extract (5 per cent) 6.90d 0.27

de 2.30

bcd


e 2.50

bcd

10. . adenophorum macerated aqueous extract (50 per cent) 10.30a 2.00

b 4.07

a


cd 2.30

bcd

GM 5.88 0.74 2.44

F value 19.79 40.33 10.59

S.E. 0.80 0.25 0.30

C.D. at 5% 1.66 0.52 0.62

Data were subjected to analysis of variance (ANOVA) and values followed by same letter(s) within a columndid not differ significantly at p0.05


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7. A. conyzoides methanolic extract (10 per cent) 1.47d 0.20

d 1.77

def

8. A. conyzoides aqueous extract (5 per cent) 1.13d 0.20

d 1.23

ef


e 1.50

def


b 12.00

a

11. . adenophorum macerated aqueous extract (100 per cent) 2.47c 0.30

cd 1.90

de

GM 2.01 0.67 3.50

F value 295.80 70.57 48.16

S.E. 0.23 0.20 0.75

C.D. at 5% 0.48 0.10 1.56

Data were subjected to analysis of variance (ANOVA) and values followed by same letter(s) within a columndid not differ significantly at p0.05

0.00

40.00

80.00

120.00

160.00

T1a T1b T2a T2b T3a T3b T4a T4b T5a T5b

Treatments

R

elativeE

longationR

atio

(Ra

dicle)

Wheat

Paddy

Maize

Figure 3: Relative elongation ratio of radicles of seedlings of test crops exposed to differentconcentrations of Eupatorium adenophorum and Ageratum conyzoides extracts

T1a: Eupatorium methanolic extract (5 per cent); T1b: Eupatorium methanolic extract (10 per cent); T2a:

Eupatorium aqueous extract (5 per cent); T2b: Eupatorium aqueous extract (10 per cent); T3a: Ageratum

methanolic extract (5 per cent); T3b: Ageratum methanolic extract (10 per cent); T4a: Ageratum aqueous extract(5 per cent); T4b: Ageratum aqueous extract (10 per cent); T5a: Eupatorium macerated aqueous extract (50 per

cent); T5b: Eupatorium macerated aqueous extract (100 per cent)

3.4 Seed vigor index

Seed vigor index of test crops under the influence of various extracts/fractions is presented in

Figure 4. There was a significant reduction in seed vigor index in case of all the treatmentsexcept E. adenophorum macerated aqueous extract (50 per cent).


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0.00

300.00

600.00

900.00

1200.00

T0 T1a T1b T2 a T2b T3 a T3b T4 a T4b T5a T5b

Treatments

SeedVigorIndex

Wheat

Paddy

Maize

Figure 4: Seed vigor index of test crops exposed to different concentrations of Eupatorium

adenophorum and Ageratum conyzoides extracts

T0: Distilled water; T1a: Eupatorium methanolic extract (5 per cent); T1b: Eupatorium methanolic extract (10 per

cent); T2a: Eupatorium aqueous extract (5 per cent); T2b: Eupatorium aqueous extract (10 per cent); T 3a:

Ageratum methanolic extract (5 per cent); T3b: Ageratum methanolic extract (10 per cent); T4a: Ageratum

aqueous extract (5 per cent); T4b: Ageratum aqueous extract (10 per cent); T5a: Eupatorium macerated aqueous

extract (50 per cent); T5b: Eupatorium macerated aqueous extract (100 per cent)

4. Discussion

The present investigation clearly indicates that treatment with various extracts/fractions of E.

adenophorum and A. conyzoides exhibit allelopathic effects on growth and physiological

potential of wheat, paddy and maize. The application of these extracts severely affected seed

germination as well as growth of emerging radicle and plumule. Among the test crops, maize

with larger seeds was less sensitive to the application of various extracts/fractions while

wheat and paddy with small seeds was more susceptible to the allelopathic effect of both

weeds. This observation is in agreement with the findings of Lucena and Doll (1976) who

found that seed size is an important factor and species with small seeds are more adversely

affected. Even complete inhibition of germination was observed in case of paddy seeds. The

test crops responded differently with the extracts. Most of the treatments significantly

reduced the germination per cent and growth of radicle and plumule. Significantly higher

stimulatory effect on plumule growth was observed for wheat seedlings and maize seedlings

exposed to E. adenophorum macerated aqueous extract (50 per cent) as compared to their

respective controls. Moreover, the inhibition of seed germination and seedling growth was

concentration dependent and more inhibition was observed at higher concentrations of all the

treatments. These results correlated with the earlier reports indicating that allelopathy is a

concentration-dependent phenomenon and includes both stimulatory and inhibitory activities

(Rai and Triputhi, 1984; Rizvi and Rizvi, 1987).

Various treatments except macerated aqueous extract of E. adenophorum had more inhibitory

effect on the growth of radicle as compared to that of plumule. Root growth has been found


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to be more sensitive to allelochemicals. They respond more strongly to small variation in

toxin concentration (Zackrisson and Nilsson, 1992).

There was a significant reduction in seed vigor index of all the test crops in case of various

treatments except seed vigor index of maize when exposed to E. adenophorum macerated

aqueous extract (50 per cent). Reduced seed germination and seed vigor index of test cropsunder laboratory conditions indicate the accumulation of toxic allelopathic substances of the

donor plant, which is harmful to the growth of seedlings of receptor plants (Rice, 1984; Chou

and Kuo, 1986; Waller, 1987; Chou, 1992). These findings also correlated with the reports of

earlier workers who found that many species contain secondary plant products that have

allelopathic potential. Earlier workers have also reported inhibition of seed germination by

allelochemicals which may be caused by blocking hydrolysis of nutrients reserve and cell

division (Irshad and Cheema, 2004) and may cause significant reductions in the growth of

plumule and radical of various crops (Ogbe et al., 1994).

Allelopathic effects are often due to synergistic activity of allelochemicals rather than to

single compound. Under field conditions, additive or synergistic effects become significanteven at low concentrations (Einhelliing and Rasmussen, 1978). McCalla and Haskins (1964)

also suggested that allelochemicals or toxins are released from the weed by the action of

micro-organisms in soil during decomposition and these allelochemicals may lead to growth

inhibition due to interference with the plant growth processes or by reducing cell division or

auxin induced growth of roots. Kobayashi (2003) also observed that the allelochemical can

directly affect the growth of receiver plants in soil, when allelochemical is present in the soil

water so that it is directly available for absorption by the plant. Though laboratory bioassays

in allelopathic research are of great importance, long-term field studies must be carried out to

ascertain allelopathic effect.

The results of the present study correlated with the findings that crude methanolic extract ofE. adenophorum had allelopathic effect on seed germination and seedling growth of tomato

(Tijani and Fawusi, 1989). Different groups of workers have reported that E. adenophorum

contains a large amount of allelochemicals especially in the leaves, which inhibit the growth

of many plants in nurseries and plantations (Ambika and Jayachandra, 1980; Eze and Gill,

1992; Gill et al., 1993; Zhao et al., 2009). Many sesquiterpene derivatives, inhibitory to some

plants have been extracted and isolated from E. adenophora (Bohlmann and Gupta, 1981;

Berdoloi et al., 1985; Baruah et al., 1994). It was observed that the terpenes inhibit growth by

suppressing cell elongation and cell division (Muller and Hauge, 1967).

Similarly, allelochemicals from A. conyzoides have been reported to inhibit seed germination

and seedling growth of many plants (Wei et al., 1997; Batish et al., 2006). Significant amountof water-soluble phenolics are reported to be present in A. conyzoides infested soil, leaf

debris, and debris-amended soils (Batish et al., 2009). The release of phenolic compounds

adversely affects the germination and growth of plants through their interference in energy

metabolism, cell division, mineral uptake and biosynthetic processes (Rice, 1984).

Sivagurunathan et al., (1997) reported that not only the nature of phenolics but also their

concentration decides the inhibitory effect. Our study is in agreement with earlier studies

where leaf debris of A. conyzoides have been reported to deleteriously affect the early growth

of rice (Batish et al., 2009) and wheat (Singh et al., 2003) by releasing water-soluble phenolic

acids into the soil environment and not through soil nutrient depletion. Xuan and coworkers

(2004) have also reported allelopathic effect of A. conyzoides leaves on paddy weeds.

Further, allelopathic potential of A. conyzoides is found to increase under unfavorable


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growing conditions (during autumn and winter) while the resistant ability of tested plants to

the allelochemicals decreases under such conditions and vice versa (Hu and Kong, 2002).

4. Conclusion / Suggestions/ Findings

The present study provides the evidence of allelopathic potential of E. adenophorum and A.conyzoides on the three agricultural crops, namely, wheat, paddy and maize. The allelopathic

activity of plant extracts is due to the various phytotoxic compounds present in the extracts

which may independently or jointly contribute to plant growth regulatory effect and inhibit

germination. Further investigation is needed to identify the active compound(s) of the

extracts responsible for their activity and to examine the effect of extracts of these weeds

against a wider range of receptor plants. The effect of these weeds on the germination and

seedling growth of these crops in the natural environment where additive or synergistic

effects become significant even at low concentrations should also be investigated. It is also

suggested that these crops should not be planted close to weeds due to adverse effects on their

growth.

Acknowledgement

The financial assistance provided by the Department of Biotechnology, New Delhi,

Government of India, for funding the research project is duly acknowledged.

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Kakatoch Allelopathic