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Int. J. Cur. Tr. Res (2015)4 (1):82-93 ISSN:2278-8042 www.injctr.com Allelopathic inhibition of Parthenium hysterophorus L. aqueous leaf extracts on germination and growth in certain crops/weed plants Malarkodi E*. and A. Manoharan Department of Plant Biology and Plant Biotechnology, Presidency College (Autonomous), Chennai, Tamil Nadu, India. Received: 15 December, 2015 Accepted: 21 December 25 2015/ Published online 24 December 2015. © INJCTR – 2015 Abstract In the present study allelopathic effect of Parthenium hysterophorus L. aqueous leaf aqueous extract on the seed germination, vigour index, seedling growth, fresh weight and dry biomass changes of three crop plants Sesamum indicum L., Arachis hypogaea L., Zea mays L., and a crop field weed Trianthema portulacastrum L. (Bishkhapra) by conducting pot culture experiments. Germination bioassays were carried out under laboratory conditions with Petri dishes. The crop/weed seeds were sown and uniformly irrigated with different concentrations like, (i.e., 2 %, 4 %, 6 %, 8 % and 10 %) of aqueous leaf extracts of Parthenium hysterophorus including control. Extracts of up to 10 % concentrations showed significant reductions in germination percentage, vigour index, shoot length, root length fresh weight and dry biomass compared with distilled water treated control except for the 2 % treated Sesame plants have a marginal increase. The highest seed germination was observed in Sesamum indicum followed by Arachis hypogaea, Zea mays and Trianthema portulacastrum. Maximum germination inhibition was observed in Trianthema portulacastrum (90.00 %). The results shows directly proportion to the concentration of leaf extract. If leaf extracts concentration increases the percentage of germination decreases in all four seeds of tested plants. Keywords: Parthenium hysterophorus, leaf extracts, Allelopathy, germination, Sesamum indicum, Arachis hypogaea, Zea mays and Trianthemum portulacastrum. Introduction Weeds are one of the most serious problems in agricultural production. They are volunteer plants from the wild or semi culture species that are found in food crops despite the will of the people and harm reducing yields. Today, some 30,000 species of weeds, i.e. repeated more than crops and in quantity, size and distribution are second group after natural vegetation. According to the FAO from the total losses worldwide caused by the crop pests, the weeds account for 35 % of losses in wheat, 28 % in vegetables, 29 % in fruit species and vineyards and 37 % in tobacco (Petrova et al., 2015). Weeds are of much more importance in crop production due to their adverse effects on crops, a term referred to as ecological *[email protected] interference. Allelopathy is the form of interference by which one plant exert its suppressive effect on another plant via a chemical inhibitor released from living or decaying tissue of donor plant (Zimdahl, 2007). It is considered to be one of the factors whereby weeds adversely affect crop growth through allelochemicals released as vapors, leachates, exudates or decomposition products from the aerial parts, foliage, roots, or dead plant residues of weeds, respectively. Usually, leaves, roots and seeds are rich source of allelochemicals compared with flowers and fruits (Rao, 2000). Congress grass, Parthenium hysterophorus L. of the family Asteraceae (tribe: Heliantheae), is an erect and much branched 83 Malarkodi and Manoharan annual or ephemeral herb, known for its notorious role as environmental, medical and agricultural hazards. It is believed to have been introduced into India and Australia from North America and in the last few years the weed has emerged as the seventh most devastating weed in Africa, Asia and Australia. Control of Parthenium has been tried by various methods, but no single management option would be adequate to manage Parthenium and there is a need to integrate various management options. Successful management of this weed can only be achieved by an integrated approach with biological control as the key element (Kaur et al., 2014). Parthenium hysterophorus L. is a well known weed that is a serious problem in agriculture. It also produces a toxin called parthenin (Lalitha et al., 2012). Most commonly used method of proving allelopathic interference in plant communities or in the "weed-crop plant" is establishing stimulating or inhibitory effect of extracted plant material on the test plants or study the effect of plant residues and their application in quartz sand and/or soil made in the laboratory (Kalinova et al., 2012). The present study has been aimed at investigating the allelopathic effect of aqueous extract of leaves from Parthenium hysterophorus L. against three crop plants Sesamum indicum L., Arachis hypogaea L., Zea mays L., and a crop field weed Trianthema portulacastrum L. (Bishkhapra) to assess the allelopathic effect of P. hysterophorus on seed germination and growth characters and assess the tolerance limit of seeds to aqueous plant extract. Materials and Methods Selection of species Four species of fast growing angiosperm plants were selected for to assess the allelopathic potential of their leaves of Parthenium hysterophorus L. as follows: (1) Sesamum indicum L. (2) Arachis hypoaea L. (3) Zea mays L. (4) Trianthema portulacastrum L. (Bishkhapra). Int. J. Cur. Tr. Res (2015)4 (1):82-93 Preparation of aqueous leaf extracts Aqueous means- dissolved in water (it can be either fresh leaves or dried powder), the collected leaves of Parthenium hysterophorus were shade dried completely for the period of 30 days than chopped into small pieces and made into fine coarse powder. Various concentrations of leaf extracts prepared (i.e., 2 %, 4 %, 6 %, 8 % and 10 % leaf powder/litre) in a flask for 48 hrs at room temperature (300C) using distilled water for the bioassay studies. Distilled water was used as a control. Pot culture experiments Earthen pots (30 ×15 cm) were filled with 5 kg of normal garden soil having silt, humus and sand mixed with Farm yard manure (FYM) in the ratio of 5:1. Healthy and uniform seeds of test plants were chosen, the seeds were surface sterilized with 0.1 % HgCl2 solution for 30 seconds and washed in distilled water thoroughly for several times to remove excess of chemical and dried to eliminate fungal attack. Then the crop/weed seeds were sown (15/pots) and uniformly irrigated with different concentrations (i.e. 2 %, 4 %, 6 %, 8 % and 10 %) of aqueous leaf extracts of Parthenium hysterophorus and five replicates were maintained to each treatment including control. The control pot was irrigated with distilled water. The leaf extracts / distilled water were added to the pots on alternate days up to 15 days. Germination was recorded after five days after seed sown. Growth parameters such as root length and shoot length, dry biomass, number of leaves and fresh weight, Photosynthetic pigment (chlorophyll) and biochemical constituents of test crop/weed seedlings such as sugars, protein, amino acids, proline and enzymes- catalse, peroxidase, polyphenol oxidase and SOD activity were estimated on 15, 30 and 45 DAS, day after germination. The physio-chemical properties of experimental pot soil were analyzed on 15th day after sown. Germination Percentage Collection of plant material The percentage of germination was calculated by using the following formulae. The plant parts of Parthenium hysterophorus were collected from agricultural fields of Vellore District, Tamil Nadu. The seeds of Sesame, Ground nut, Maize and Trianthemum were produced from Tamil Nadu agricultural University, Coimbatore, Tamil Nadu, India. Seeds were selected as uniform in size, colour and weight and stored in metal tins as suggested by Rao (1956). Number of seeds germinated Germination (%) =------------------------------------- x 100 Vigour Index Number of seeds sown The seedling vigour index was calculated by using Abdul–Baki and Anderson (1973) formulae. SVI= (Shoot length (cm) + Root length (cm) X Germination percentage. Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan Shoot length and Root length Five seedlings of each test crop namely Sesame, Groundnut, Maize and Trianthemum were selected randomly from each treatment of pot culture experiment. The shoot length and root length was measured with scale and thread which were expressed in centimeters. Fresh and Dry Biomass The seedlings were up rooted and washed thoroughly with tap water. The randomly selected five normal seedlings were used for measuring root and shoot length were used for recording fresh weight as well as dry weight of seedlings and expressed in milligrams. Dry weight of five seedlings was recorded after drying in hot air oven maintained at 800C temperature for 48 hours. The dried seedlings were weighed, averaged and expressed in milligrams. The dry weights were recorded by using an electronic single pan balance. Statistical analysis At least five replicates were maintained for all treatments and control. The depth if significance between the treatments could be brought out clearly by multiple ranges testing programme. Hence, ANOVA followed by Tukey’s Multiple Range Test (TMRT) was applied for the experimental data at 5 % level of significance (Zar, 1984). Results The seed germination, vigour index and growth parameters of all the test plants, influenced by the leaf extracts were recorded on 15, 30 and 45 days after seed sown (DAS). The data gathered from periodical observations were processed and statistically analyzed and the results are presented in the tables. The observations and results of the present investigation are as follows. Seed germination The germination percentage of four test plants was influenced by the aqueous leaf extracts of P. hysterophorus and the results are presented in the Table 1. The highest seed germination was observed in Sesamum indicum followed by Arachis hypogaea, Zea mays and Trianthema portulacastrum. The increasing concentration of leaf extracts of P. hysterophorus increased the reduction percentage on crops/weed germination. Among the 4 species the highest inhibitory percentage was noticed in Sesamum indicum (94.00 %) which was followed by Arachis hypogaea (92.00 %), Zea mays (90.00 %) and Trianthema 84 portulacastrum (90.00 %) when compared to control plants. The germination percentage of all the tested plants gradually declined up to 10 % concentration of leaf extracts. However, 2 % aqueous leaf extracts of Sesame showed the highest germination percentage (96.77 %) (Table 1). Vigour index Changes in the vigour index of four tested plants cultivated in aqueous leaf extracts of P. hysterophorus are given in Table 2. The maximum vigour index was observed in Sesamum indicum followed by Arachis hypogaea, Zea mays and Trianthema portulacastrum. The vigour index of all the test plants gradually declined with increasing concentration of leaf extracts. Among the 4 species the highest inhibitory percentage was noticed in Sesamum indicum (3714.36) with 2 % concentration of leaf extracts which was followed Arachis hypogaea (3445.74), Zea mays (3443.18) and Trianthema portulacastrum (2388.28) in control plants. The vigour index of all the tested plants gradually declined up to 10 % concentration of leaf extracts (Table 2). Root length The root length of all the four experimental plants reduced against the aqueous leaf treatments of P. hysterophorus and data shown in the Table 3. The highest root length was observed in Sesamum indicum followed by Arachis hypogaea, Zea mays and Trianthema portulacastrum. When compared to control, the root length was progressively reduced with increasing the level of leaf extracts. The maximum inhibitory effect of root length was observed in Zea mays (188.18 %) significantly at 10 % of concentration and followed by Trianthema portulacastrum (168.12 %), Arachis hypogaea (164.86) and Sesamum indicum (54.63 %) after 45 days of cultivation. However, 2 % concentration of leaf extracts of Sesame showed highest root length (19.00 cm/plant) when compared to control plants (Table 3). Shoot length The shoot length of all the four experimental plants reduced against the aqueous leaf treatments of P. hysterophorus and data shown in the Table 4. The highest seed germination was observed in Zea mays followed by Sesamum indicum, Arachis hypogaea and Trianthema portulacastrum. When compared to control, the root length was progressively reduced with increasing the level of leaf extracts. When compared to control, the maximum inhibitory effect of root length was observed in Arachis hypogaea (124.15 %) which was followed by Trianthema portulacastrum (63.77 %), Zea mays (62.95 %) and Sesamum Malarkodi and Manoharan 85 indicum (50.04 %). However, 2 % concentration of leaf extracts of Sesame showed highest shoot length (38.19 cm/plant) when compared to control plants (Table 4). Fresh weight Table 5 shows the fresh weight of all the four experimental plants reduced against the aqueous leaf treatments of P. hysterophorus. Maximum fresh weight was observed in Zea mays followed by Sesamum indicum, Arachis hypogaea and Trianthema portulacastrum. When compared to control, the fresh weight was progressively reduced with increasing the level of leaf extracts up to 10 % concentration of leaf extracts (except for 2 % of Sesame 44.9 g/plant). The maximum inhibitory effect of fresh weight was observed in Trianthema portulacastrum (86.09 %) followed by Arachis hypogaea (61.27 %), Zea mays (43.12 %) and Int. J. Cur. Tr. Res (2015)4 (1):82-93 Sesamum indicum (41.14 %) after 45 days growth period. Dry biomass Similar to fresh weight, the dry weight of all the four experimental plants reduced against the aqueous leaf treatments of P. hysterophorus and also maximum dry weight was observed in Zea mays followed by Sesamum indicum, Arachis hypogaea and Trianthema portulacastrum. When compared to control, the dry weight was gradually reduced with increasing the level of leaf extracts up to 10 % concentration of leaf extracts (except for 2 % of Sesame 14.9 g/plant). The maximum inhibitory effect of fresh weight was observed in Trianthema portulacastrum (88.93 %) followed by Arachis hypogaea (61.53 %), Zea mays (45.39 %) and Sesamum indicum (40.84 %) after 45 days growth period (Table 6). Table-1 Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on seed germination (%) percentage of four crop/ weed species Parthenium hysterophorus S. No Extract Concentration Sesame Groundnut Maize Trianthemum 1 Control 94a 92a 90a 90a 2 2% 96.77a (-1.28) 89.82b (-2.37) 87.85b (-2.38) 86.14b (4.29) 3 4% 92.93a (-3.19) 87.14b (-4.19) 84.33c (-6.29) 81.32c (-9.64) 4 6% 89.05b (-7.23) 82.54c (-10.28) 77.72d (-13.64) 74.43d (-17.29) 5 8% 72.77c (-24.19) 65.15d (-29.18) 59.13e (-34.29) 54.48e (-39.46) 6 10% 48.34d (-49.64) 39.33e (-57.24) 34.03f (-62.18) 28.62f (-68.19) Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control Table-2 Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on vigour index of four crop/ weed species S. No Extract Concentration 1 Control 2 2% 3 4% 4 6% 5 8% 6 10% Parthenium hysterophorus Sesame Groundnut Maize Trianthemum 3335.36a 3714.64a (-3.85) 3121.14b (-13.07) 2867.92c (-37.08) 2018.63d (-63.97) 1148.67e (-75.11) 3445.74a 3344.44a (-3.96) 3130.55b (-5.54) 2645.50c (-17.42) 1764.68d (-42.39) 859.88e (-69.28) 3443.18a 3388.14a (-5.12) 3162.68b (-10.97) 2606.41c (-27.76) 1683.64d (-55.63) 800.56e (-81.44) 2388.28a 1997.61a (-6.84) 1723.62b (-14.31) 1510.61c (-32.91) 1021.11d (-63.72) 465.93e (-87.43) Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan 86 Table-3 Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on Root length (cm/plant) of four crop/weed species Parthenium hysterophorus Extract Concentra Sesame Groundnut Trianthemum Maize tion Control 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 5.26a 8.29a 18.1a 5.2a 8.26a 14.94a 4.9a 9.61a 14.18a 3.1a 7.4a 12.28a 6.25a 10.22a 19.00a 5.40a 9.98a 15.61a 4.80a 9.27a 13.87a 3.06a 7.21a 12.09a (-0.3) (-0.96) (-0.53) (-2.28) (-2.01) (3.35) (-2.13) (-3.56) (-2.48) (-1.27) (-2.59) (-1.56) 5.21a 8.10a 17.75a 4.93a 7.56b 13.96b 4.60b 8.63b 12.96b 2.97a 6.79a 11.64a (-1.25) (-2.35) (-1.94) (-5.27) (-8.49) (-6.64) (-6.19) (-10.23) (-8.59) (-4.27) (-8.29) (-5.21) 3.99b 7.39b 16.54b 4.19b 5.92c 11.78c 3.84c 6.74c 10.57c 2.66b 5.57b 10.26b (-6.28) (-10.96) (-8.61) (-19.41) (-28.37) (-21.16) (-21.65) (-29.84) (-25.49) (-14.28) (-24.67) (-16.49) 3.69c 6.02c 14.55c 3.11c 4.55d 8.89d 2.78d 4.84d 7.90d 1.95c 4.31c 7.46c (-13.46) (-27.38) (-19.62) (-40.19) (-44.97) (-40.51) (-43.28) (-49.67) (-44.28) (-37.18) (-41.79) (-39.28) 3.16d 4.85d 11.72d 2.14d 2.96e 6.03e 1.85e 2.89e 4.94e 1.60d 2.89d 4.58d (-25.83) (-41.52) (-35.26) (-58.94) (64.17) (-59.61) (-62.18) (-69.94) (-65.17) (-48.27) (-60.89) (-54.18) 2% 4% 6% 8% 10% Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control. Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan 87 Table-4. Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on shoot length (cm/plant) of four crop/weed species Parthenium hysterophorus Extract Concentra Sesame Groundnut Trianthemum Maize tion Control 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 10.8a 23.5a 41.5a 9.8a 20.5a 37.9a 12.8a 25.4a 45.8a 8.8a 18.5a 34.8a 12.6a 25.8a 44.9a 8.7a 18.5a 35.9a 11.8a 24.9a 43.2a 8.2a 16.3a 30.2a (-0.92) (-1.02) (-0.96) (-1.08) (-2.49) (-1.05) (-0.52) (-0.72) (-0.62) (-1.68) (-3.59) (-2.18) 11.7b 22.5b 39.8b 7.2a 16.8a 32.9a 10.9a 22.0b 41.8b 7.5a 15.8a 27.3 (-1.76) (-5.61) (-4.21) (-2.14) (-6.47) (-3.19) (-1.04) (-2.67) (-2.09) (-5.28) (-13.40) (-8.42) 10.4c 20.5c 38.0 7.0b 15.9b 29.4b 10.0c 21.5c 39.8c 7.0b 13.2b 26.2b (-10.52) (-21.37) (-18.53) (-10.48) (-17.29) (-12.52) (-4.53) (-7.19) (-5.28) (-15.25) (-25.65) (-19.18) 8.5d 16.0d 32.8d 6.5c 15.0c 28.9c 9.2d 19.9d 35.9d 6.7c 12.8c 22.5c (-21.39) (-32.53) (-22.96) (-24.69) (-34.18) (-29.17) (-8.17) (-23.64) (-17.56) (-34.54) (-44.20) (-36.67) 7.3e 14.2e 29.4e 5.8d 13.1d 23.5d 8.6e 17.3e 32.0e 5.2d 10.9d 18.7d (-30.64) (-51.86) (-33.49) (-43.19) (-59.19) (-58.27) (-20.17) (-37.68) (-31.28) (-64.52) (-72.18) (-66.28) 2% 4% 6% 8% 10% Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan 88 Table-5. Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on fresh weight per plant (gm/plant) of four crop/weed species Partheniumhysterophorus Extract Concentra Sesame Groundnut Maize Trianthemum tion Control 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 3.6a 7.8a 13.8a 3.2a 6.8a 12.6a 4.2a 8.4a 15.2a 2.9a 6.1a 11.6a 4.2a 8.6a 14.9a 2.9a 6.1a 11.9a 3.9a 8.3a 14.4a 2.7a 5.4a 9.06a (-0.92) (-1.02) (-0.96) (-1.08) (-2.49) (-1.05) (-0.52) (-0.72) (-0.62) (-1.68) (-3.59) (-2.18) 3.9b 7.5b 13.1b 2.4a 5.6a 10.9a 3.6a 7.3a 13.9b 2.5a 5.2a 9.1a (-1.76) (-5.61) (-4.21) (-2.14) (-6.47) (-3.19) (-1.04) (-2.67) (-2.09) (-5.28) (-13.40) (-8.42) 3.4c 6.8c 12.6c 2.3b 5.3b 9.8b 3.3b 7.1c 13.2c 2.3c 4.4c 8.7b (-10.52) (-21.37) (-18.53) (-10.48) (-17.29) (-12.52) (-4.53) (-7.19) (-5.28) (-15.25) (-25.65) (-19.18) 2.8d 5.3d 10.9d 2.1d 5.0d 9.6c 3.0d 6.6d 11.9d 2.2c 4.2c 7.5c (-21.39) (-32.53) (-22.96) (-24.69) (-34.18) (29.17) (-8.17) (-23.64) (-17.56) (-34.54) (-44.20) (-36.67) 2.4e 4.7e 9.8e 1.9d 4.3d 7.8d 2.8e 5.7e 10.6e 1.7d 3.6d 6.2d (-28.64) (-48.86) (-31.49) (-41.19) (-57.19) (-56.27) (-18.17) (-35.68) (-29.28) (-62.52) (-70.18) (-62.28) 2% 4% 6% 8% 10% Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control. 89 Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan Table-6 Allelopathic effects of aqueous leaf extracts of Parthenium hysterophorus on dry weight per plant (gm/plant) of four crop/weed species Partheniumhysterophorus Extract Concentr ation Control Sesame Groundnut Maize Trianthemum 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 15DAS 30DAS 45DAS 3.6a 7.8a 13.8a 3.2a 6.8a 12.6a 4.2a 8.4a 15.2a 2.9a 6.1a 11.6a 4.2a 8.6a 14.9a 2.9a 6.1a 11.9a 3.9a 8.3a 14.4a 2.7a 5.4a 9.06a (-0.92) (-1.02) (-0.96) (-1.08) (-2.49) (-1.05) (-0.52) (-0.72) (-0.62) (-1.68) (-3.59) (-2.18) 3.9b 7.5b 13.1b 2.4a 5.6a 10.9a 3.6a 7.3a 13.9b 2.5a 5.2a 9.1a (-1.76) (-5.61) (-4.21) (-2.14) (-6.47) (-3.19) (-1.04) (-2.67) (-2.09) (-5.28) (-13.40) (-8.42) 3.4c 6.8c 12.6c 2.3b 5.3b 9.8b 3.3b 7.1c 13.2c 2.3c 4.4c 8.7b (-10.52) (-21.37) (-18.53) (-10.48) (-17.29) (-12.52) (-4.53) (-7.19) (-5.28) (-15.25) (-25.65) (-19.18) 2.8d 5.3d 10.9d 2.1d 5.0d 9.6c 3.0d 6.6d 11.9d 2.2c 4.2c 7.5c (-21.39) (-32.53) (-22.96) (-24.69) (-34.18) (29.17) (-8.17) (-23.64) (-17.56) (-34.54) (-44.20) (-36.67) 2.4e 4.7e 9.8e 1.9d 4.3d 7.8d 2.8e 5.7e 10.6e 1.7d 3.6d 6.2d (-28.64) (-48.86) (-31.49) (-41.19) (-57.19) (-56.27) (-18.17) (-35.68) (-29.28) (-62.52) (-70.18) (-62.28) 2% 4% 6% 8% 10% Mean with different alphabets in a column differed significantly as per Tukey’sMultiple Range Test (TMRT) (P<0.05). Data in parenthesis indicates % decrease/increase over respective control Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan Discussion In general, leaves are the most potent source of allelochemicals, however, the toxic metabolites are also distributed in all other plant parts in various concentrations. In this regard, aqueous leaf extracts of Parthenium hysterophorus L. was evaluated for their allelopathic potential on germination, seedling growth, morphologicalcharacters of important crop plants, Sesamum indicum, Arachis hypogaea and Zea mays and a weed Trianthemum portulacastrum which are commonly cultivated in Vellore District of Tamil Nadu, India. Seed germination Seed is defined as a fertilized ovule, or as a miniature plant surrounded by food reserve and protected by seed coat. From the seed, new generation of the plant begins. To fulfil this role, seed possesses some special physiological and biochemical properties. For example, it has very low water content and metabolic rate but remains viable and regain the normal metabolism required for growth and development into a plant, when it gets favourable condition for germination. Seed germination is considered to be the most critical stage especially under stress conditions. Germination is the process by which a plant grows from a seed. The inhibition of germination of the four test crops/ weeds was observed in fifth day with all the treatments (except for 2 % concentration of sesame). Results of the present study showed that, significant inhibition on seed germination was observed in all the four test plants exposed with various concentrations of aqueous leaf extracts of P. hysterophorus. The similar results were obtained by the application Eucalyptus leaf extracts on cowpea, sorghum, pearl millet, wheat, barley, potato, groundnut, maize, sunflower and mustard (Del Moral and Muller, 1970; Rao and Reddy, 1984; Igboanugo, 1988; Suresh and Raj, 1987; Puri and Khara, 1991 and Jayakumar et al., 1990). The allelopathic effect of Casuarina and Teak sp. on other plant species was studied by number of authors (Almousawi and Al Naib, 1975, 1976; Devasagayam and Ebenezar, 1996; Huang et al., 1997; Patg et al., 2000 and Floretine, 2003). These results are accordance also with the results of Teucrium chamaedrys (Fioerentino et al., 2009), Sterculia foetida (Usha Rani et al., 2011), Parthenium hysterophorus and Chromolaena Odorata (Devi et al., 2014) Achyrantuhs aspera (Tanveer et al., 2014) and legume crops (Mondal et al., 2015). Chui-Hua et 90 al. (2007) discussed that extracts were more harmful to weeds extracts, which may be due to the presence of allelochemicals such as alkaloids, amino acids, carbohydrates and phytohormones at higher concentrations in shoots. Mishra and Singh (2010) reported that the extracts of leaf, stem, flower and fruit of Lantana camara inhibited the seed germination of Parthenium hysterophorus clearly indicated that due to the allelochemicals present in the extracts adversely affected the seed germination. Maximum seed germination observed in control. Earlier works reported that Parthenium has deadly allelopathic effects on rice, wheat, chickpea, soyabean and mustard (Karim and Forzwa, 2010; Biswas, 2010). There was a gradual decrease in seed germination and different growth parameter with the increase in concentration of Parthenium leaf and stem extracts. Vigour index Results from present investigation vigour index crops/weed plants were gradually reduced with the concentrations of aqueous leaf extracts of P. hysterophorus. However the 2 % concentration of sesame plants showed the increase of vigour index. Similar results was also observed from Djanaguiraman et al. (2002) who found a similar type of result that E. globule reduced the vigour index in green gram, black gram and cowpea. A similar inhibitory effect of Digera muricata on sorghum was reported by Karthiyayini et al. (2003). Das et al. (2012) reported that with the increasing the concentration of leachate of Shorea robusta, the vigour index of the Cicer aretinum decreased. The vigour index of all the four seedlings may be due to reduced seed germination and shoot length, as vigour index is the product of germination and seedling growth. Seedling growth In the present investigation seedling growth of crops/weed plants were gradually reduced with the concentrations of aqueous leaf extracts of P. hysterophorus. However, the 2 % concentration of sesame plants showed the increase of shoot length and root length also. The studies of the morphology and plant growth characteristics are fundamental to any investigation for physiological basis of allelopathic potential of plants. In the present study, inhibition of shoot and root growth of four crops/weeds upon exposure to allelopathic plant aqueous leaf extracts may be attributed to phytochemicals present in Parthenium. Inhibition of seedling growth in allelopathy stress conditions may be therefore a result of 91 Malarkodi and Manoharan decreased ion uptake. Darier (2002) recorded significant suppression of nutrient uptake by Vicia faba and Zea mays when treated with aqueous extract of Eucalyptus rostrata. Patel et al. (2002) reported that Eucalyptus trees reduced the growth and yield of wheat crop. Some acids of the Parthenium may present in the shoot and which may be involved in the root and shoot reduction of the crop plants. Allelopathic effects of compounds are often observed to occur early in the life cycle, causing inhibition of seedling growth. Dos Santosh et al. (2004) reported that the allelochemicals inhibit absorption of ions. The reduction of plant growth in the presence of allelochemicals is associated with the strong inhibition of mitosis or/and disruption of the structure of organelles (Gniazdowska and Bogatek, 2005). It has been reported that incorporation of Parthenium residue significantly reduced shoot growth of different species of Brassica (Singh et al., 2005) and concluded that Parthenium dry biomass considerably depressed germination percentage and speed of germination index of maize, while fresh and dry weight of maize were affected only at higher concentration of dry biomass used in soil. Further, the root growth was reduced more than shoot, since the root is the first organ to come into contact with phytochemicals in the rhizosphere (Gniazdowska and Bogatek, 2005). The phytochemical can reduce cell division or auxin synthesis that induces the growth of shoot and roots (Gholami et al., 2011). Mishra (2015) reported in Lantana camara, the allelopathic effect of plant growth performance includes root length, shoot length, intermodal length, leaf number, fresh weight and dry weight. The growth parameters were significantly reduced in seedling which was raised from seeds pretreated with leaf extracts and leaf leachates of each concentration. Dry biomass The fresh weight and dry weight of crops/weeds were drastically declined and the maximum reduction was observed in Trianthema plats and maximum shoot length and root length was observed in 2 % concentration of Sesame. The inhibitory effects may be due to the presence of phenolic compounds in the extracts, which might inhibit the activity of GA3 (Einhelling, 1986) or inhibit the synthesis of GA3 and regulate the alpha amylase production during seed germination (Chandler et al., 1984). Beres and Kazinczi (2000) reported that the aqueous shoot extract of Rumex obsefolius and Asclepias syriaca reduced the seedling fresh and dry weight of corn. Phytochemicals present in the extracts Int. J. Cur. Tr. Res (2015)4 (1):82-93 may inhibit or decrease elongation, expansion and division of cells which are growth prerequisite (Qasem and Hil, 1989), also inhibit absorption of ions (Dos Santosh et al., 2004) and therefore, resulted in arrested growth of root and shoot of crop and growth of weed seedlings. The disruption of growth and development of crop/weed seedlings during phytochemical stress can modify the mitochondrial respiration leading to decreased supply of ATP for all energy demanding processes (Gniazdowska and Bogatek, 2005). Allelopathic effects of Parthenium hysterophorus L. aqueous extracts on soybean (Glycine max L.) and haricot bean (Phaseolus vulgaris L.) seed germination, shoot and root growth and dry matter production was reported by Netsere and Mentesil, 2011. The loss of seedling dry weight of weeds and rice may be due to the osmotic effect (Fatemeh et al., 2012). Smilarly, Acacia auriculiformis and Gliricidia sepium leaf leachates decreased shoot and root fresh and dry weights of maize over control (Oyum, 2007). The reduction of plant growth by the presence of allelochemicals in the extracts can exhibit the strong inhibition of mitosis or/and disruption of the structure of organelles e.g. nuclei and mitochondria (Gniazdowska and Bogatek, 2005). The allelochemicals can retard respiration and photosynthesis, resulting in decreased ATP production which is bound to alter other cell processes which are energy demanding and ultimately (Bogatek et al., 2002). This concept favors the present findings. Manimegalai (2013) found that significant reduction was noticed on fresh and dry biomass of Vigna mungo and V. radiata exposed to aqueous extract of Tectona grandis. Arpana (2014) reported that, aqueous extract of Lantana camara caused severe inhibitory effect on seedling length and biomass of Pisum sativum. This biomass reduction could be the inhibitory effect of phytochemicals on uptake of water by seedlings and reduction in other physiological processes. Conclusion Based on these results, it can be concluded that allelopathy is a concentration development phenomenon, as increased concentration of the P. hysterophorus aqueous leaf extract treatment their potential of allelopathic effects increased gradually as a detrimental manner. P. hysterophorus aqueous leaf extracts affected all the growth parameters (germination, vigour index, seedling growth, Fresh and dry biomass studied in the four test crops/weed as compared to their respective control. Among the four test plants, the maximum reduction percentage and biochemical constituents were observed in Sesame followed by groundnut, Int. J. Cur. Tr. Res (2015)4 (1):82-93 Malarkodi and Manoharan maize and Trianthema. However, the 2 % leaf extract of Sesamun indicum plants exhibited the marginal increase in all tested parameters. 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