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Biological control of Parthenium i: effect of Imperata cylindrica on distribution, germination and seedling growth of Parthenium hysterophorus L.

Tehmina Anjum, Rukhsana Bajwa and Arshad Javaid

Department of Mycology & Plant Pathology, Quaid-e-Azam Campus, University of the Punjab, Lahore-54590, Pakistan, www.pu.edu.pk Email anjum@mpp.pu.edu.pk

Abstract

Natural products have been the source of many pesticides, used either directly as crude preparations or as pure compounds. The present study was undertaken to evaluate prospects of control of Parthenium hysterophorus by using crude preparations of Imperata cylindrica (L). Beauv., an allelopathic grass. Ecological survey revealed that frequency and density of P. hysterophorus was significantly lower in I. cylindrica dominating localities as compared to nearby areas without I. cylindrica infestation. Aqueous extracts of I. cylindrica exhibited the potential to control germination and seedling growth of P. hysterophorus. Root and shoot aqueous extracts of all the applied concentrations significantly suppressed the germination of P. hysterophorus. Early seedling growth of P. hysterophorus was generally reduced significantly by extracts of 10% and of higher concentrations. Increasing the concentration of the extract increased the inhibitory potential. Shoot extract was found more inhibitory than root extract.

Media summary

Allelopathic potential of Imperata cylindrica can be use as natural product source for weed management.

Key Words

Parthenium hysterophorus, Imperata cylindrica, weed, allelopathy

Introduction

Weeds are problematic in various ways. In recent years a new weed species, Parthenium hysterophorus has been reported to be rapidly spreading in Pakistan (Shabir 2003). This weed is generally infesting wastelands in Pakistan and there is not any report at present that this weed is a problem in crops. There is, however, threat that this weed may invade agricultural lands in Pakistan in future. Although chemical herbicides are effective in controlling weeds yet risks are involved in their usage. Due to increased awareness about the risks involved in the use of pesticides, nowadays there is much emphasis to search for alternate methods of weed control, which are safe for the environment. Allelopathy has been recognized as a natural weed control approach (Akhtar et al. 2001).

Imperata cylindrica is an aggressive perennial grass that is distributed throughout Pakistan from plains up to 2000 meters in the chir-pine zone. It is a common weed and a wasteland species growing especially on poorly drained soils (Hussain and Abidi 1991). Harlan (1975) reported that I. cylindrica suppresses the seedling growth and root sprouting of forest trees and associated species. Sajise and Lale (1975) observed that I. cylindrica reduces the growth of Stylosanthus guyanensis in mixed cultures. Hussain and Abidi (1991) reported that I. cylindrica exhibit allelopathy against Setaria italica, Dicanthium annulatum, chrysopogon montanus, Medicago polymorpha and Pinus roxburghii. They identified Caffeic, ferulic, p-hydroxybenzoic, p-coumaric, vanillic, chlorogenic and syringic acids as the allelopathic agents. During surveys of different P. hysterophorus infested areas, we observed a marked reduced density of P. hysterophorus at I. cylindrica dominating localities as compared to nearby areas without the infestation of this grass. We hypothesized that this low density of P. hysterophorus at I. cylindrica dominating localities could be due to allelopathic nature of this grass. The present study was, therefore, undertaken to investigate the allelopathic effects of aqueous extracts of I. cylindrica on germination and early growth of P. hysterophorus.

Materials and Methods

Analysis of Imperata dominated communities

Three I. cylindrica dominating sites were selected near Lahore along the bank of BRB Canal for phytosociological study. At each locality the frequency and density of P. hysterophorus was estimated by using 0.5 x 0.5 m quadrate. Data regarding the frequency and density of P. hysterophorus was also recorded from nearby areas without I. cylindrica infestation. The frequency and density of P. hysterophorus was then determined along with other weed species in herb zone and I. cylindrica dominating zone.

Aqueous extract bioassays

Shoot (leaves and stem) and roots (including rhizomes) extracts of I. cylindrica were obtained by soaking 25g fresh plant material in 100 ml sterilized water for 48 hours at room temperature. Extracts were filtered and diluted to 20, 15, 10 and 5% by adding distilled water and stored at 4C. Seeds of P. hysterophorus were sown on twice folded filter paper seedbeds in sterilized petri dishes. Tests were moistened with aqueous root and shoot extracts of different concentrations while control received distilled water. There were three replicate plates with 10 seeds each. Dishes were incubated at 25C for one week. At the end of the experiment germination, root and shoot length, and seedling biomass was recorded. Data were analyzed by applying Duncan’s Multiple Range Tests (Steel and Torrie 1980).

Results and Discussion

Analysis of Imperata dominated communities

Data presented in Table 1 revealed that the P. hysterophorus had markedly lower values of absolute and relative frequency as well as absolute and relative density in I. cylindrica dominating localities as compared to nearby areas without infestation of this grass. Similarly other weed species, except Cyanodon dactylon, were found less frequently in I. cylindrica dominating zone. Most of the species present in non-Imperata zone were entirely lacking in I. cylindrica dominating zone. Similar reduction in frequency and density of associated species in I. cylindrica dominating localities has also been reported by Harlan (1975) and Hussain and Abidi (1991).

Table 1: Frequency and density of P. hysterophorus and other weeds in herb and Imperata zones.

Species

Non - Imperata zone

Imperata zone

 

AF

RF

AD

RD

AF

RF

AD

RD

Parthenium hysterophorus L.

90

19.5

87

45

20

10

2.8

9

Achyranthus aspera L.

30

6.5

1.5

0.80

0

0

0

0

Amaranthus viridus L.

30

6.5

2.2

1.1

0

0

0

0

Boerhaavia diffusa L.

20

4.4

0.7

0.36

0

0

0

0

Chenopodium album L.

10

2.2

5.0

0.26

0

0

0

0

Conyza ambigua DC

10

2.2

2.0

1.1

20

10

0.4

1.3

Cyanodon dactylon L.

100

22

70

36

90

45

25

80

Cyprus rotundus L.

30

6.5

19

l0

0

0

0

0

Euphorbia pilulifera L.

10

2.2

0.2

0.1

0

0

0

0

Euphorbia prostrata L.

10

2.2

0.8

0.4

0

0

0

0

Launea nudicalus Less

10

2.2

0.3

0.15

0

0

0

0

Malvestrum coromandelianum

50

11

4.7

2.4

10

5

.5

1.6

Oxalispes-caprae L.

0

0

0

0

10

5

1

3.2

Setaria glauca L.

40

8.7

3.7

1.9

10

5

0.2

0.6

Setaria verticillata L.

10

2.2

0.8

0.4

10

5

0.2

0.6

Sonchus arvensis L.

10

2.2

0.3

0.15

30

15

1

3.2

AF: Absolute frequency RF: Relative frequency AD: Absolute density RD: Relative density

The decline in frequency and density of P. hysterophorus and other associated species at I. cylindrica dominating localities can be attributed to some allelopathic interaction Other allelopathic grasses like Cenchrus ciliaris L. and Bothriochloa pertusa (L.) A. Camus are also known to suppress and preclude the associated species (Hussain et al. 1982). Recently Javaid et al. (2004) have reported similar low frequency of P. hysterophorus and other weed species at Desmostachya bipinnata (allelopathic grass) dominating localities.

Figure 1. Effect of aqueous extracts of Imperata cylindrica on germination and early seedling growth of Parthenium hysterophorus (Vertical bars show standard errors. Bars with different letters show significant difference as determined by DMR Test).

Aqueous Extract bioassays

Root and shoot aqueous extracts of all the applied concentrations significantly suppressed the germination of P. hysterophorus. Generally increase in the concentration increased the inhibitory potential of the extracts. Shoot extract was more inhibitory than root extract. There was 31 – 80% reduction in germination of the test weed species due to shoot extracts as compared to 30 – 48% reduction due to root extract of I. cylindrica (Figure 1A). The greater inhibitory effect of aqueous extracts of aerial parts on germination than the effect of sub-aerial parts has also been reported in other plant species (Noor and Khan 1994). It could be attributed to different types and/or different concentrations of allelochemicals in root and shoot.

Aqueous extracts of the I. cylindrica suppressed the shoot and root length of the seedlings. The effect of the lowest concentration (5%) of both root and shoot extract was insignificant. However, inhibitory effect of rest of the concentrations was found significant except effect of 10% root extract on shoot length. The inhibitory potential of extracts generally enhanced with increase in concentration (Figure 1B & C). The reduction in seedling roots and shoot length may be attributed to the reduced rate of cell division and cell elongation due to the presence of allelochemicals in the aqueous extracts (Buckolova 1971). Seedling biomass was also adversely affected by the extracts. All the concentrations of the shoot extract significantly suppressed the shoot biomass of the seedlings. By contrast, the effect of lower concentrations of 5 and 10% root extract on seedling biomass of the test species was insignificant (Figure 1D). Shoot extracts were generally more toxic to seedling shoot and root growth of the test species. Shoot extract of 25% showed highest inhibitory potential resulting in 94, 87, and 88% reduction in shoot length, root length and seedling biomass, respectively (Figure 1B – D). The reduced seedling growth could be attributed to the presence of phenolic allelochemicals in I. Cylindrica (Inderjit and Dakshini, 1991). Since these allelochemicals are soluble in water, they are leached from living and decomposing plant materials by rain water and accumulate in the soil underneath the grass cover where they can express toxicity against P. hysterophorus and other coexisting species. Similarly germination and growth suppression of P. hysterophorus due to aqueous extracts of three allelopathic grasses namely Dicanthium annulatum, Cenchrus pennisiformis and Sorghum helepense have been reported by Bajwa et al. (2004). The present study clearly indicates that allelochemicals present in I. cylindrica have the potential to suppress germination and plant growth of P. hysterophorus. Further studies are required isolate and evaluate the inhibitory potential of the different allelochemicals present in I. cylindrica, against germination and growth of P. hysterophorus. The effective natural product would then be used as environment friendly herbicides to control the noxious weed P. hysterophorus.

References

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