Abstracts

INTRODUCTION

Parthenium hysterophorus, a member of the Asteraceae family, is commonly known as carrotgrass, whitehead weed, congress grass, or parthenium weed. This weed has invaded about 30 countries in Africa, Australia and Asia, including Pakistan (Chippendale & Panetta, 1994CHIPPENDALE, J. F.; PANETTA, F.D. The cost of parthenium weed to the Queensland cattle industry. Plant Protec. Quart., v. 9, n. 2, p. 73-76, 1994.; Shabbir & Bajwa, 2007SHABBIR, A.; BAJWA, R. Parthenium invasion in Pakistan - a threat still unrecognized. Pakistan J. Bot., v. 39, n. 7, p. 2519-2526, 2007.; Nigatu et al., 2010NIGATU, L. et al. Impact of Parthenium hysterophorus on grazing land communities in north-eastern Ethiopia. Weed Biol. Manage., v. 10, n. 3, p. 143-152, 2010.). Parthenium is an obnoxious weed rapidly spreading across the non-cropped areas of the Khyber Pakhtunkhwa province and elsewhere in Pakistan; where it has caused serious damage to pastures, crops and biodiversity (Khan et al., 2012KHAN, H. et al. Chemical control of Parthenium hysterophorus L. at different growth stages in non-cropped area. Pakistan J. Bot., v. 44, n. 5, p. 1721-1726, 2012.; Masum et al., 2013MASUM, S. M. et al. Threats of Parthenium hysterophorus on agro-ecosystems and its management: a review. Intern. J. Agric. Crop Sci., v. 6, n. 11, p. 684-697, 2013.). Yield losses due to the presence of this weed in various crops range from 33 to 90% (Tamado et al., 2002TAMADO, T. et al. Interference by the weed Parthenium hysterophorus L. with grain sorghum: Influence of weed density and duration of competition. Intern. J. Pest Manage., v. 48, n. 1, p. 183-188, 2002.; Vivek et al., 2008VIVEK R, S. et al. Effect of weed interference on weeds and productivity of blackgram (Phaseolus mungo). Indian J. Weed Sci., v. 40, n. 1-2, p. 65-67, 2008.; Khan et al., 2013). In addition, it also causes allergy, dermatitis and asthma in human and cattle due to its poisonous nature (Suresh et al., 1994SURESH, P. et al. Bronchial provocation with Parthenium pollen extract in bronchial asthma. Indian J. Chest. Dis. Allied Sci., v. 36, p. 104, 1994.; Evans, 1997EVANS, H.C. Parthenium hysterophorus: a review of its weed status and the possibilities for biological control. Biocont News Infor., v. 18, n. 3, p. 89-98, 1997.; Khan et al., 2013).

It is an alien invasive weed spreading throughout Pakistan in both irrigated and rainfed areas (Shabbir & Bajwa, 2007; Khan et al., 2012). Its presence as an aggressive colonizer in both non-cropped and cropped situations has been well documented (Javaid & Anjum, 2005JAVAID, A. et al. Herbicidal effects of extracts and residue incorporation of Datura metel against parthenium weed. Nat. Prod. Res., v. 24, n. 15, p. 1426-1437, 2010.; Riaz & Javaid, 2010RIAZ, T.; JAVAID A. Prevalence of invasive parthenium weed in district Hafizabad, Pakistan. J. An. Plant Sci., v. 20, n. 2, p. 90-93, 2010.; Khan et al., 2014). The widespread invasion of parthenium weed in natural grasslands, field crops, orchards and vegetable fields in the country has prodded weed scientists to devise strategies for its management. Although parthenium weed can be successfully controlled with herbicides (Sharma, 2003SHARMA, R. Performance of different herbicides for control of congress grass (Parthenium hysterophorus L.) in non-cropped areas. Indian J. Weed Sci., v. 35, n. 3-4, p. 242-245, 2003.; Javaid et al., 2007; Kathiresan, 2008KATHIRESAN, R. Ecology and control of Parthenium hysterophorus invasion in veeranum command area. Indian J. Weed Sci., v. 40, n. 1-2, p. 78-80, 2008.; Khan et al., 2012), chemical control however is not recommended due to its detrimental effects on the environment and human health. In order to minimize the usage of synthetic herbicides, plant extracts alone or in combination with herbicides should be used. These extracts contain potential allelochemicals such as phenolics, terpenoids, alkaloids, coumarins, tannins, flavonoids, steroids and quinines (Xuan et al., 2005XUAN, T. D. et al. Biological control of weeds and plants pathogens in paddy rice by exploiting plant allelopathy: an overview. Crop Protec., v. 24, n. 3, p. 197-206, 2005.), which are capable of selectively and non selectively influencing plant germination and growth at various concentrations, often at very small concentrations.

Studies have been carried out using various herbaceous plants extracts for their phytotoxic effect against parthenium weed (Anjum et al., 2006; Javaid et al., 2005; Quazi & Khan, 2010QUAZI, S. M.; KHAN, M.A. Suppression of Parthenium hysterophorus L. by Alternanthera polygonoides (L) R. Br. Bioinfolet, v. 7, n. 1, p. 91, 2010.; Shafique et al., 2011SHAFIQUE, S. et al. Tagetes erectus L. - a potential resolution for management of Parthenium hysterophorus L. Pakistan J. Bot., v. 43, n. 2, p. 885-894, 2011.). Some of these such as Amaranthus spinosus, Imperata cylindrica, Desmostachya bipinnata, Dichanthium annulatum, Cenchrus pennisetiformis, Physalis minima, Sorghum halepense, Tagetes erectus and Xanthium strumarium were found effective against this weed. Nevertheless, the degree and nature of phytotoxic action of aqueous extract of a plant varies by plant part (Sinha & Singh, 2004SINHA, N. K.; SINGH, S. Allelopathic effects of Xanthium strumarium on Parthenium hysterophorus. Indian J. Plant Physiol., v. 9, n. 3, p. 313-315, 2004.; Swain et al., 2005SWAIN, D. et al. Effects of Physalis minima on Parthenium hysterophorus. Allelop. J., v. 15, n. 2, p. 275-283, 2005.) and extract concentration (Safdar et al., 2013SAFDAR, M. E. et al. Tree species as a potential source of bio-herbicides for controlling Parthenium hysterophorus L. Nat. Prod. Res., v. 27, n. 22, p. 2154-2156, 2013.). Hence, there is a need to test other well-known allelopathic plants to explore their potential phytotoxic activity against parthenium weed. Therefore, some herbaceous plant species were evaluated for their pre and postemergence herbicidal activity against parthenium weed.

MATERIALS AND METHODS

Germination and seedling growth bioassays were conducted using four herbaceous species viz., Achyranthes aspera, Alternanthera philoxeroides, Datura metel, and Rumex dentatus in petri plates and pots. Studies were carried out at Weed Science Laboratory, Department of Agronomy, University of Agriculture, Faisalabad, Pakistan during 2011 12.

Preparation of aqueous extracts

Wild growing plants of each species were collected and kept at room temperature for drying and then oven-dried at 70 ^oC for 48 h. Intact plants of those species were then separated into root, stem, leaves and fruit. However, of A.philoxeroides into root, stem and leaves as fruit were absent in it. Some whole plants of all plant species were also kept intact. These were then cut into small (2 cm) pieces and separately soaked in distilled water at a ratio of 1: 20 w/v (herbage:water) for 24 h at room temperature (Hussain & Gadoon, 1981HUSSAIN, F.; GADOON, M.A. Allelopathic effects of Sorghum vulgare. Pers. Oecologia, v. 51, n. 3, p. 284-288, 1981.). Aqueous extracts (5% w/v) of different plant parts were obtained by filtering the mixture using an ASTM 40 mesh sieve and then through Sartorious Minisart syringe filters with 0.45 µm pore size.

Determination of biochemical characteristics of aqueous extracts

The pH and EC of each extract were determined with a pH meter (JENWAY 3510 pH Meter) and an EC meter (JENWAY 3510 conductivity Meter), respectively. Total soluble phenolics were determined as described by Randhir & Shetty (2005)RANDHIR, R.; SHETTY, K. Developmental stimulation of total phenolics and related antioxidant activity in light and dark germinated maize by natural elicitors. Proc. Biochem., v. 40, n. 5, p. 1721-1732, 2005. and expressed as gallic acid equivalents (Table 1). For identification and quantification of their suspected phytotoxins, aqueous extracts were chemically analysed using a Shimadzu HPLC system equipped with a UV detector (Model SCL-10A, Tokyo, Japan). The peaks were identified using chemical standards (Aldrich, St Louis, USA). The concentration of each isolated compound (Table 2) was determined using the following equation:

Biochemical characteristics of aqueous extracts of parthenium plant parts and their rhizospheric soils from various farm locations and their phenolic compositions are presented in Tables 1 and 2.

Germination studies

To evaluate preemergence herbicidal potential against parthenium, 5% aqueous extracts of root, stem, leaves, fruit and whole plant of A. aspera, D. metel and R. dentatus and root, stem, leaves and whole plant of A. philoxeroides were used in the germination bioassay. Twenty seeds of parthenium were placed in 9 cm dia. Petri plates lined with a double layer of Whatman No. 10 filter paper and moistened with 4 mL of each extract. A control treatment with 4 mL of distilled water was included. Each treatment was replicated 4 times and the plates arranged in a completely randomized design with a factorial arrangement of species X extract concentration. Petri plates were kept in an illuminated incubator maintained at 25±5 ^oC. Germination was recorded daily for 20 days. Germination count data were used to calculate various seed germination and vigor parameters as detailed below:

Germination percentage (GP) was calculated by the following formula:

GP = [N_T x 100]/N (eq. 2)

where N_T: proportion of germinated seeds in each treatment for the final measurement, and N: Number of seeds used in the bioassay.

The germination index (GI) was calculated by following the formula as described by Scott et al. (1984)SCOTT, S. J. et al. Review of data analysis methods for seed germination. Crop Sci., v. 24, n. 6, p. 1192-1198, 1984.:

GI = N₁ / D₁+....................+N_L / D_L (eq. 3)

where N₁: number of seeds germinated in 1st count, D₁: days to 1st count, N_L: number of seeds germinated in last count, and D_L: days to last count.

Mean germination time (MGT) was calculated by the following equation, as given by Dezfuli et al. (2008)DEZFULI, P. M. et al. Influence of priming techniques on seed germination behavior of maize inbred lines (Zea mays L.). ARPN J. Agric. Biol. Sci., v. 3, n. 3, p. 22-25, 2008.:

MGT = ΣDn/Σn (eq. 4)

where n: Number of seeds which were germinated on day D, D: Number of days counted from the beginning of the germination.

Time to 50% germination (T₅₀) was calculated according to the following formula modified by Farooq et al. (2005)FAROOQ, M. et al. Thermal hardening: a new seed vigor enhancement tool in rice. J. Integr. Plant Biol., v. 47, n. 2, p. 187-193, 2005.:

T₅₀ = t_i+ {(N/2) - n_i} (t_j - t_i) /n_j-n_i (eq. 5)

where N: Final number of germination, n_i, n_j: cumulative number of seeds germinated by adjacent counts at times t_i and t_j when n_i<N/2<n_j.

Seedling growth studies

Leaf extracts of A. philoxeroides, D. metel and R. dentatus, and whole plant extract of A. aspera were tested for their postemergence herbicidal potential against parthenium weed through seedling growth bioassay in pots kept in the Laboratory. Twenty seeds of parthenium weed were sown in plastic pots (10 cm dia. and 10 cm depth) filled with 650 g sandy loam soil per pot initially moistened with 200 mL of distilled water. Each treatment was replicated four times and the experimental units were arranged in a completely randomized design. Three seedlings were maintained per pot. The 4 mL aqueous extract of each plant species was sprayed over 15 days-old parthenium weed seedlings. Seedlings in control treatment were also sprayed with distilled water in a similar way. Minimum and maximum temperatures during the course of experiments were 23 ^oC and 41 ^oC, respectively. Ten days after spraying, 25-d-old seedlings were uprooted from pots and their shoot and root lengths were recorded. Shoot and root dry weights were recorded after drying them in an electrical oven at 65 ^oC for 48 h. Germination percentage and seedling length were used to calculate seedling vigor index (SVI) by the following formula, as described by Orchard (1977)ORCHARD, T. Estimating the parameters of plant seedling emergence. Seed Sci. Technol., v. 5, n. 1, p. 61-69, 1977.:

SVI = [seedling length (cm)

× germination percentage] (eq. 6)

Data Analysis: The data collected were statistically analysed using Fisher's analysis of variance technique in the MSTATC Software Program. Treatment means were compared on the basis of least significant difference (LSD) at the 0.05 probability level (Steel et al., 1997STEEL, R. G. D. et al. Principles and procedures of statistics. A Biometrical Approach. 3.ed. New York: McGraw Hill Book, 1997. 672 p.).

RESULTS AND DISCUSSION

Germination Assay: Table 3 presents data on various germination traits, including germination percentage (GP), germination index (GI), mean germination time (MGT), and time to 50% germination (T₅₀). Regardless of the plant tissue used, aqueous extract of A.aspera caused maximum reduction in parthenium GP (92%) compared with the distilled water treated control (DWTC) (Table 3). However, A.philoxeroides delayed the germination of parthenium weed, the most (GI = 1.6, MGT = 11.8 d and T₅₀ = 11.7 d). Extracts from leaves were most effective among the plant tissues used, regardless of species, as significantly lower GP (25.8) and GI (11.3) while higher MGT (7.9 d) and T₅₀ (7.7 d) were noted with parthenium weed seeds in response to leaf extracts (Table 3). With regard to species x plant part interaction means, all plant parts of R.dentatus and root extract of A.aspera, A.philoxeroides and D.metel proved least potent inhibitors of parthenium weed germination percentage (Table 3). Germination inhibition by aqueous extracts of A. aspera has also been reported by Chandra et al. (2011)CHANDRA, S. et al. Hormetic impact of Achyranthes aspera L. extracts on seed and seedling traits of Vicia faba L. Columban J. Life Sci., v. 2, n. 1/2, p. 87-91, 2011. in broad bean (Vicia faba). Mandal & Mondal (2011)MANDAL, A.; MONDAL, A.K. Taxonomy and ecology of obnoxious weed Alternanthera Philoxeroides Grisebach (Family Amaranthaceae) on spore germination in Ampelopteris Prolifera (Ketz.) Cop. Adv. Biores., v. 2, n. 1, p. 103-110, 2011. also found that aqueous extracts from stem, root, leaves and inflorescence of A. philoxeroides were found to inhibit the germination of Ampelopteris prolifera.

Seedling bioassay: The significantly highest shoot length (4.3 cm), root length (5.6 cm), shoot dry weight (18.4 mg) and root dry weight (2.2 mg) of parthenium weeds were recorded with a distilled water sprayed control (Table 4). On the contrary, maximum inhibition in shoot length (68%), shoot dry weight (96%), seedling biomass (96%), and seedling vigor index (98%) of parthenium weeds were observed with an extract from whole plant of A.aspera. Whereas parthenium weed seedlings sprayed with R.dentatus leaf extract showed the highest suppression in root length (70%), root dry weight (96%) and seedling length (68%) compared with the distilled water sprayed control. These values did not differ significantly with those noted in parthenium weed seedlings in response to A.aspera whole plant extract. Reduction in root and shoot lengths and biomass of broad bean (Vicia faba) by aqueous plant extract of A.aspera at higher concentrations was also reported by Chandra et al. (2011), whereas retardation in seedling growth of A. prolifera through the application of aqueous extracts from stem, root, leaves and inflorescence of A. philoxeroides was also found by Mandal & Mondal (2011). Seedling growth inhibition in terms of reduced plumule and radicle lengths of wheat in pea by application of aqueous extracts of root, stem and leaves of R.dentatus has also been documented by Umer et al. (2010)UMER, A. et al. Evaluation of allelopathic potential of some selected medicinal species. African J. Biotechnol., v. 9, n. 37, p. 6194-6206, 2010.. Javaid et al. (2010), in laboratory and foliar spray bioassay studies, have proved that aqueous extracts of D.metel have significantly reduced germination and seedling growth of parthenium weed.

Germination and seedling growth inhibitory effects of aqueous extracts of A.aspera and A.philoxeroides on parthenium weed may be due to their higher total phenolic contents (2618 to 5779 mgL^-1) (Table 1), presence of gallic (16.9 mgL^-1), caffeic (7.4 mg L ¹⁾, chromatotropic (13.8 to 63.8 mg L ¹⁾, p-coumaric (10.5 mg L^-1), m coumaric (3.1 mg L^-1), syringic (9.2 mg L^-1) and 4-hydroxy-3-methoxy benzoic (24.8 to 118.6 mg L^-1) acids in their aqueous extracts (Table 2). Achyranthine is the major alkaloid present in all tissues of A.aspera whereas other allelochemicals in various plant parts are phenolics, oleonolic acid, dihydroxy ketones, long chain compounds and saponin A and B (Ali, 1993ALI, M. Chemical investigation of Achyranthes aspera Linn. Oriental J. Chem., v. 9, n. 1, p. 84-85, 1993.; Srivastav et al., 2011SRIVASTAV, S. et al. Achyranthes aspera-An important medicinal plant: A review. J. Nat. Prod. Plant Res., v. 1, n. 1, p. 1-14, 2011.).

Based on preemergence and postemergence activities against parthenium, whole plant extract of A.aspera and leaf extract A.philoxeroides are concluded as herbicidal. Therefore, these extracts should be further tested alone or in combination with existing synthetic herbicides for sustainable and eco friendly management of parthenium weeds.

ACKNOWLEDGMENTS

This manuscript is part of a thesis by the principal author for his PhD degree in the Department of Agronomy, University of Agriculture, Faisalabad, Pakistan. The authors of this manuscript greatly acknowledge Dr. Razia Riaz, Research Officer, Hi Tech. Laboratory, University of Agriculture, Faisalabad, Pakistan for her kind cooperation in providing facilities for HPLC studies.

Publication Dates

History