Pak. J. Weed Sci. Res. 11(1-2): 75-79, 2005

BIOLOGICAL CONTROL OF PARTHENIUM IV: SUPPRESSIVE ABILITY OF AQUEOUS LEAF EXTRACTS OF SOME ALLELOPATHIC TREES AGAINST GERMINATION AND EARLY SEEDLING GROWTH OF PARTHENIUM HYSTEROPHORUS L.

Sobiya Shafique, Rukhsana Bajwa, Arshad Javaid

and Shazia Shafique

       ABSTRACT

Aqueous extract bioassays were conducted to evaluate the allelopathic potential of five tree species viz. Azadirachta indica  (L.) A. Juss., Ficus benghalensis L., Melia azadarach L., Mangifera indica L. and Syzygium cumini (L.) Skeels., for their use in Parthenium hysterophorus L. control, one of the world’s worst weeds. Aqueous extracts of 2, 4, 6, 8 and 10% (w/v), obtained from dry leaves of test tree species were bioassayed on P. hysterophorus seeds. Toxicity of the aqueous extracts was assessed by recording their effect on germination, radicle and plumule length, and seedling biomass of the test weed species. Aqueous extracts of 8 and 10% concentrations of all the test tree species invariably and significantly (P ≤ 0.05) suppressed germination of P. hysterophorus seeds. Extracts of F. benghalensis and M. indica were proved more inhibitory than rest of the test species, where extract of lowest concentration of 2% significantly suppressed the germination. Extracts of M. azadarach were found most effective in suppressing the radicle and plumule growth of P. hysterophorus followed by S. cumini and F. benghalensis.

Key words: Parthenium, alleleopathy, plant extracts, growth inhibition.

INTRODUCTION

Parthenium hysterophorus L., originating in the area around the Gulf of Mexico, has invaded Asia, Africa and Australia during the last 50 years. It was introduced in subcontinent in 1955 through imported food grains. At present this weed is rapidly spreading in Punjab and NWFP, Pakistan. It occurs widely along the roadsides, on wastelands and sometimes in field crops. The high dominance of this weed may be attributed to its aggressive behaviour, very high seed production potential and suppressive effects on neighbouring plant through allelopathic interaction (Evans, 1997).  This weed is known to have adverse impact on ecosystems and agricultural crops (Chippendale and Panetta, 1994).  The chemical analysis has indicated that all the plant parts including trichomes and pollens contain toxins called sesquiterpene lactones. The major components of toxin being ‘Parthenin’ and other phenolic acids such as caffeic acid, vanillic acid, anisic acid, chlorogenic acid and parahydroxy benzoic acid are lethal to human beings and animals and also cause allelopathic effects on neighbouring plants (Oudhia, 1998).

Allelopathy plays an important role in regulating plant diversity (Chou and Lee, 1991). In the beginning most of the allelopathic research was conducted to investigate the effect of weeds on crops and one crop on another. However, at present the allelopathic crop and weed residues are being utilized for weed control in crops. Cheema et al., (1997) found that aqueous extracts of sorghum and sunflower has the potential to suppress the weed infestation in wheat crop. Similarly Akhtar et al., (2001) showed that aqueous extracts of Cirsium arvense and Ageratum conyzoides could suppress the germination and early seedling growth of some weeds of wheat. Moradshahi et al. (2003) found that aqueous extracts of Eucalyptus camaldulensis Schlecht. has the potential to suppress growth of Echinochloa crus-galli (L.) Beauv., Avena fatua L. and Rumex acetosella. Similarly Dahiya and Narwal, (2003) found that root exudates of Helianthus annuus L. are allelopathic towards Agropyron repens (L.) Beauv., Ambrosia artemsiifolia L., Avena fatua L., Celosia crustata, Chenopodium album L., Cynodon dectylon (L.) Pers. The objective of the present study was to assess the potential of aqueous extracts of five allelopathic trees viz. A. indica, F. benghalensis, M. azadarach, M. indica and S. cumini to control the germination and early seedling growth of P. hysterophorus.

MATERIALS AND METHODS

Fresh leaves of five allelopathic trees viz. Azadirachta indica, Ficus benghalensis, Melia azadarach, Mangifera indica and Syzygium cumini (Hussain et al., 1985; Mushtaq et al., 1993; Bajwa et al., 1999) were collected from University of the Punjab, Quaid-e-Azam Campus Lahore, Pakistan. After thorough washing with sterilized water, leaves were dried in an oven at 40 °C till constant weight. To obtain a 10% (w/v) aqueous extract, 10 g crushed dry leaf material of each of the five test species was soaked in 100 ml distilled water for 36 hours at 25 ⁰C and filtered. Further dilutions of 8, 6, 4 and 2% (w/v) were prepared by adding appropriate quantity of distilled water to the 10% stock solution. The extracts were stored at 4⁰C.

Seeds of P. hysterophorus were sown on a filter paper seedbed in sterilized petri dishes. The filter papers were moistened with aqueous leaf extracts of the test allelopathic trees. Control was treated similarly with distilled water. There were three replicates of each treatment with 10 seeds per petri plate. The plates were incubated at 25 ⁰C for 14 days. Plates were regularly checked for moisture. Germination, root and shoot length, and seedling fresh biomass were recorded at the end of the experiment. Data were analyzed statistically by applying Duncan’s Multiple Range Test (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

Effect on germination

Aqueous extract of all the five test tree species exhibited allelopathic potential against the germination of P. hysterophorus. However, extracts of all test species were not equally toxic against the germination of the test weed. Extracts of F. benghalensis and M. indica were more inhibitory than extracts of remaining test species. The extract of lowest concentration of 2% of these two test species also significantly retarded the germination of P. hysterophorus. The most effective treatment in suppressing germination of test weed was 10% extract of F. benghalensis where germination was reduced to 5% as compared to 100% in control (Fig. 1A). Similar inhibitory effects of  aqueous extracts of allelopathic grasses viz. Dicanthium annulatum Stapf., Cenchrus pennisetiformis Hochest, Sorghum halepense Pers., Imperata cylindrica (L). Beauv. and Desmostachya bipinnata Stapf on germination of P. hysterophorus have also been reported (Anjum et al., 2005; Javaid et al., 2005; Javaid and Anjum, 2005).

Effect on seedling growth

Fig. 1:   Effect of aqueous leaf extracts of five allelopathic trees on germination and early seedling growth of P. hysterophorus

Aqueous extracts of M. azaderach proved most effective in reducing both plumule and radicle length of P. hysterophorus seedlings. All the applied concentrations of 2-10% aqueous extract significantly declined the plumule and radicle length. Generally toxicity of the extract increased by increasing the concentrations (Fig. 1B-D). Among the rest of the tree species, extracts of F. benghalensis and S. cumini were very effective in retarding plumule and radicle length. All except 2% concentration of these tree species significantly suppressed plumule length (Fig. 1B). Similar impact of F. benghalensis extracts was recorded on radicle length also. However, aqueous extracts of all concentrations significantly declined radicle length of test weed (Fig. 1C). Effect of aqueous extract of M. azaderach, S. cumini and F. benghalensis on seedling biomass was similar to that of their effect on plumule and radicle length (Fig. 1D). Recently Anjum et al. (2005) and Javaid and Anjum (2005) have also reported similar reduction in seedling growth of P. hysterophorus due to aqueous extracts of allelopathic grasses The reductions in seedlings root 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).

Aqueous extracts of A. indica were least toxic exhibiting a non-significant negative impact on both plumule and radicle length (Fig. 1 B & C). However, seedling biomass of P. hysterophorus was significantly reduced by 10% extract of A. indica (Fig. 1D). Similarly, extracts of M. indica failed to significantly retard the plumule and radicle length, as well as seedling biomass of P. hysterophorus. Conversely lower concentrations of 2-6% of this test tree species promoted the seedling growth of P. hysterophorus (Fig. 1 B-D).  Javaid and Anjum (2005) have reported that lower concentrations of 5 and 10% of shoot extract and 5% of root extract of Sorghum halepense stimulates plumule length of P. hysterophorus seedlings. Similar effect of aqueous extracts of Inula grantioides Boiss. and Capsicum annuum L. on seedling growth of test weed species has also been reported by Shaukat et al. (1983) and  Reigosa et al. (1999). The present study reveals that the aqueous extracts of M. azaderach, F. benghalensis and S. cumini are highly effective against germination and growth of P. hysterophorus and can be used to control this noxious weed.

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