REVIEW OF LITERATURE Allelopathy in bioassay

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1 REVIEW OF LITERATURE Competition for environmental resources apart, allelopathy, the direct or indirect effect of one plant upon the other through exudation of phytotoxic inhibitors also plays a significant role in plant interactions (Muller, 1969). It is often tacitly assumed by the protagonists of agroforestry that the addition of a tree component to a field crop situation will almost always depress the yield of the field crop even though the less may be more than compensated. Trees being the dominant partners in the association, will compete with the under storey crop for natural resources like light, water and nutrients (Lundgren and Raintree, 1983). Allelopathy in bioassay Rao and Reddy (1984) studied the effect of Eucalyptus tereticornis leaf extracts on the germination and other growth parameters of selected dry land food crops. The results revealed that leaf extracts inhibit germination of crop seeds to a certain extent. The germination per cent increased in horse gram, green gram and cowpeas, indicating that leaf extracts may have some stimulatory effect on some species of plants. Seedlings from the treated seeds in the Petri dishes died a few days after germination. Mortality was highest in pigon pea followed by coriander and beans. Compared with controls, the overall growth rate of seedlings was reduced. Heavy mortality of seedlings and reduced vigour under laboratory conditions indicates that the accumulation of toxic substances is harmful to the growth of crop plants. Gradual recovery of field-grown seedlings indicates that once the inhibitory substances are leached out from the soil harmful effects are minimized. Sharma et al., (1987) studied the effect of leachates from 4 commonly grown tree species (Acacia nilotica, E. tereticornis, Dalbergia sissoo and Morus alba) on the germination and growth of 4 crops viz., wheat (Triticum aestivum), raya (Brassica juncea), field pea (Pisum sativum) and lentil (Lens esculenta). Germination of raya was reduced by all leachates; that of other crops was not much affected. Leachates of M. alba had the most toxic effect on all crops. Generally, root and shoot length and vigour index were reduced by leachates (relative to control) in the order M. alba > D. sissoo > E.

2 tereticornis > A. nilotica. The most sensitive crop was raya, followed by lentils, field peas and wheat. Anwar (1991) tested the effect of extracts of fresh leaves and leaf litter, and of stemflow water from 3 Eucalyptus spp. (E. alba, E. deglupta and E. robusta) on growth of maize seedlings and found that E. alba was the most allelopathic species and fresh leaves were the most allelopathic 'extract'. Bisla et al., (1992) studied the inhibitory effects of aqueous extracts of dried leaves of Eucalyptus tereticornis and Populus deltoides on the seed germination and seedling growth of 5 winter crops: Triticum aestivum, Hordeum vulgare, Lens esculenta, Cicer arietinum and Brassica juncea. Activity varied with extract concentration, and, in some cases, initial stimulatory effects were obtained. Generally, the inhibitory effect of E. tereticornis was less than that of P. deltoids. Bansal et al., (1992) studied the Eucalyptus macrorrhyncha and E. youmanii extracts (at 1, 2 and 5%) for their allelopathic effect on seedling growth of Triticum aestivum and Raphanus sativus. Results showed that root and shoot growth of wheat and radish were not significantly affected by 1 and 2% extracts of E. macrorrhyncha, although root length of wheat was inhibited markedly by 5% extract and shoot length slightly. Joshi and Om Prakash (1992) studied the effect of extracts of fresh and partially decomposed litter of 10 tree species: Populus deltoids, Casuarina equisetifolia, Bombax ceiba, Syzygium cumini, E. tereticornis, Azadirachta indica, Dalbergia sissoo, Albizzia lebbeck, Leucaena leucocephala and Sesbania aculeta on the seeds of 4 agricultural crops (wheat, maize, pea and mustard). Fresh litter extracts reduced the germination of all crops, with those from E. tereticornis, S. aculeta, Azadirachta indica, L. leucocephala and P. deltoides having the greatest effect. The inhibitory effects of the fresh extracts were directly related to their content of phenolic compounds; extracts from partially decomposed litter were less inhibitory to seed germination, and also contained a smaller amount of phenolic compounds. Germination of mustard and pea seeds was more affected by both fresh and partially decomposed litter extracts than germination of wheat and maize.

3 Thakur and Bhardwaj (1992) studied the wheat and maize seeds exposed to leachates from leaf extracts of Eucalyptus globulus, Populus ciliata, Juglans regia and Robinia pseudoacacia. Wheat germination was not significantly affected by exposure to the leachates but maize germination rate was decreased to 89% when compared to control. Seedling vigour was decreased in both species by all the leachates; the greatest reduction was with J. regia leachate. Lisanework and Michelsen (1993) studied the allelopathic effect of Cupressus lusitanica, Eucalyptus globulus, E. camaldulensis and E. saligna on seed germination, radicle and seedling growth of four crops: Cicer arietinum, Zea mays, Pisum sativum and Eragrostis tef. Aqueous leaf extracts of all the tree species significantly reduced both germination and radicle growth of the majority of the crops, usually starting from concentrations of 1 or 2.5%. The shoot and root dry weight increase of the crops was significantly reduced after 10 weeks' treatment with leaf extracts. Among the four crops, chickpeas and teff were most susceptible with respect to germination, and teff with respect to growth. From the overall data the leaf extracts of the four tree species can be arranged according to increasing allelopathic potential: C. lusitanica<e. globulus<e. saligna<e. camaldulensis. Extracts made from soil samples collected from the rhizosphere of Acacia nilotica trees and of the tree bark have inhibited the seed germination and seedling growth of Cyamopsis tetragonoloba and Pennisetum glaucum (Duhan and Lakshminarayana, 1995). Malik and Shah (1995) reported that decayed leaves and their extracts of 3 species of Eucalyptus (Eucalyptus camaldulensis, Eucalyptus citriodora and Eucalyptus tereticornis), have not produced any significant inhibitory effect on various growth parameters of Phaseolus vulgaris, including yield (weight and number of pods). However, the same extracts reduced the growth of Pisum sativum in the same experiment with the maximum effect being exhibited by decayed leaves (leaf extracts) of Eucalyptus citriodora followed by Eucalyptus camaldulensis and Eucalyptus tereticornis. Mukhopadhyay et al., (1995) studied the effect of different concentrations of leaf extracts of Eucalyptus citriodora on germination of rabi crops (chickpeas, mustard and wheat), Anagallis arvensis, Chenopodium album and Spergula arvensis was investigated. Germination of rabi crops was not decreased by leaf extracts although the process was

4 delayed with increasing concentration. Germination of weed seeds decreased with increasing concentration of leaf extract from to ppm. At the highest concentration there was 20% germination compared to 80% with control. Shoot length in chickpeas, mustard and wheat was reduced by 77.48, and 68.21%, respectively at the highest concentration of extract, and root length was reduced by 86.50, and 65.87%, respectively. Srivastava et al., (1996) made the investigations of the allelopathic activities of leaf leachates Eucalyptus tereticornis, Leucaena leucocephala, Populus deltoides and Bauhinia variegate on Triticum aestivum. The inhibitory effect of leachates was concentration dependent and the trees were ranked in the order: L. luecocephala > P. deltoides > E. tereticornis > B. variegata. Shoot growth was also inhibited by 10% leachates, with L. leucocephala and P. detoides the most inhibitory. Root growth was not much affected by treatments although L. leucocephla and P. deltoides leachates significantly reduced it at 10%. Devasagayam and Ebenezar (1996) studied the laboratory experiment on seeds of sorghum, ground nuts, maize, black gram, cowpeas and soyabeans were germinated in water or Eucalyptus leaf extract (100 g/litre distilled water). Seed germination was decreased in all crops by Eucalyptus leaf extract. Ground nut and cow peas were the most tolerant (4 and 6% decrease in germination, respectively, compared with the control), whereas inhibition was highest in sorghum (16.3%) soyabeans (10.9%), maize (8.9%) and black gram (7.1%). Sunderamoorthy et al., (1996) bioassayed aqueous leachates of leaves, stem, litter, and soil from Prosopis juliflora for allelopathic properties using seeds of pearl millet and sesame. All the leachates showed some inhibitory effects; with the leaf leachates exhibited the maximum effect. Kalia et al., (1996) studied the aqueous leaf leachates of some multipurpose tree species (Acacia nilotica, Cassia siamea, Dalbergia sissoo, Eucalyptus tereticornis and Leucaena leucocephala) and found to have an inhibitory effect on the germination and seedling growth of the weed species Ageratum conyzoides. Leachates of E. tereticornis were most effective.

5 Tripathi et al., (1996) studied the inhibitory activity of 4 multipurpose forest tree species (Eucalyptus hybrid, Leucaena leucocephala, Populus deltoides and Bauhinia variegata) on the germination and seedling growth of wheat. The inhibitory activity of leaf leachates was in the order L. leucocephala > P. deltoides > E.tereticornis > B. variegata, while that of root leachates was in the order B. variegata > E. tereticornis = P. deltoides > L. leucocephala. Swaminathan (1996) studied the bark leachates of 8 multipurpose tree species on inhibition of germination and seedling growth of maize (Zea mays), pigeon pea (Cajanus cajan) and sesame (Sesamum indicum). Results showed that all the tree species inhibited germination, with Ailanthus excelsa the most inhibitory to germination and radicle growth and plumule elongation, followed by Acacia nilotica and Dalbergia sissoo. However, results varied between crops, with leachates generally inhibiting growth of sesame most, and pigeon peas least. The other tree species included in the test were Acacia leucophloea, Bauhinia sp., Casuarina equisetifolia, Eucalyptus tereticornis and Tectona grandis. Huang ZhuoLie et al., (1997) while studying the leaf extracts of Eucalyptus urophylla were shown to inhibit the rooting rate, root number and the length of roots of mung bean cuttings by 85.71, and 93.52%, respectively, rooting rate of pea cuttings by 100%, and inhibit the germination rate of Indian mustard (Brassica juncea var. napiformis) and wild cabbage (Brassica oleracea var. caulorapa) seeds by and 60.72%, respectively. Leaf extracts of kalanchoe (Kalanchoe pinnata) inhibited the root length of mung bean cuttings by 38.12%, inhibited the rooting rate, root number, and root length of pea cuttings by 14.23, and 26.90%, respectively, and the germination rates of Indian mustard and wild cabbage seeds by and 53.60%, respectively. Leaf extracts of Setcreasea purpurea promoted the rooting rate, root number, and root length of pea cuttings by , and 22.05%, respectively. Stem extracts of Eucalyptus urophylla and Kalanchoe pinnata inhibited root growth and decreased root length of mung bean (Vigna radiata) and pea cuttings. Mung bean root numbers were decreased by E. urophylla extracts but increased by K. pinnata extracts. E. urophylla extracts inhibited seed germination in wild cabbages (Brassica oleracea var. caulorapa) and K. pinnata extracts inhibited the germination of Brassica juncea and wild cabbages.

6 Sajjan et al., (1997) investigated the effects of aqueous extracts of Eucalyptus spp. stem and leaves on seed germination and seedling growth in Pennisetum glaucum, sorghum, sunflower and soyabeans. Leaf extracts were more effective than stem extracts in reducing germination and seedling growth. P. glaucum was most tolerant and sunflower was most susceptible to Eucalyptus extracts. Ibrahim et al., (1999) studied the allelopathic effects of Eucalyptus camaldulensis and E. microtheica leaf and litter extract on seed germination of Sorghum bicolor and Sorghum sudanense (Sudangrass). Effects of these species and Conocarpus lancifolius on Sorghum spp. dry matter production were also studied under field conditions. Results showed that Eucalyptus leaf and/or litter extracts significantly reduced percentage germination of both Sorghum species when applied at high concentration and/or when leaves and litter were soaked for long periods in water. On the other hand, differences in germination of Sorghum species planted in soil samples collected from bare soil (control) and Eucalyptus plantation soil were not significant. Results of field experiments showed that there were no significant differences in dry matter production of the two Sorghum species between completely felled Eucalyptus and Conocarpus plantations (residue containing) and the control (residue free) plots in Kassala and Fawar areas. However, partially felled Eucalyptus and Conocarpus plantations significantly depressed dry matter production relative to the control and the completely felled treatments. These differences were attributed to a significant reduction in the amount of intercepted solar radiation by Sorghum spp. in partially felled plots. John and Nair (1999) conducted the experiments to assess the allelopathic effects of aqueous leaf extracts of 14 agroforestry tree species, using germination and seedling growth of rice cv. Jyothi and cowpea cv. Kanakamony as bioassays. Results indicated that all extracts inhibited the rice germination and plumule and radicle elongation, with Ailanthus triphysa, Tamarindus indica, Acacia auriculiformis and Thespesia populnea having most effect. Seven species inhibited cow pea germination, plumule and radicle growth with Eucalyptus tereticornis and T. indica producing the strongest effects. Allolli and Narayanareddy (2000) studied the allelopathic effects of various concentrations of plant extracts isolated from leaves, barks and roots of Eucalyptus spp. on the germination and seedling growth of cucumber seeds. With respect to germination

7 and seedling growth of cucumber in response to different sources of extracts, concentration and their interaction effects were significantly different. Effect of leaf extracts of Eucalyptus was most detrimental on the germination and seedling growth of cucumber. Treatment with 10% leaf extract resulted in the lowest percentage of germination (41.0%) and shoots (6.95 cm) and root (7.12 cm) growth. Allolli et al., (2000) studied the effect of Eucalyptus tereticornis leaf, bark and root extracts at 4 concentration gradients (1.0, 2.5, 5.0 and 10.0%) on germination and growth of garlic. The lowest germination, root and shoot length of garlic was observed in treatments with leaf extract, while the highest germination was observed in the control. The extracts at 10% concentration resulted in the lowest germination percentage. Bhatt and Chauhan (2000) tested the allelopathic influence of Quercus glauca and Q. leucotrichophora on three crops: wheat (Triticum aestivum); mustard (Brassica campestris); and lentil (Lens culinaris). In bioassay studies, aqueous extracts of dried/ fresh leaves, leaf litter and flaked off bark suppressed the germination, plumule and radicle length of all test crops. In pot culture, soil amended with leaf litter and bark also suppressed the germination, shoot length and dry mater of test crops. The rhizosphere soil of both trees also significantly suppressed the pigment contents and dry matter of all test crops. Sharma et al., (2000) investigated the allelopathic effects of 3 and 4 year old poplar (Populus deltoides) on wheat. The aqueous extracts of partially decomposed poplar leaves retarded the germination and growth of wheat. Relatively more retardation was noticed with extracts from partially decomposed leaves and the magnitude of reduction was greater during the initial stages of decomposition. Irrespective of decomposition stage, the adverse effect was intensified with increasing concentration of extracts. Germination and growth of wheat were suppressed by extracts of soil sampled from a distance of 0-3 m from a 3 year old plantation, which further intensified and was extended up to 6 m in the fourth year. Channal et al., (2000) studied the allelopathic effect of leaf extracts from Azadirachta indica, Acacia Arabica, Eucalyptus tereticornis, Tamarindus indica, Tectona grandis, Samanea saman and Syzygium cumini, all applied at 5 and 10% concentration, on seed germination, vigour index, seedling length, and seedling dry matter of sorghum

8 and rice. Irrespective of concentration, all tree leaf extracts promoted germination in sorghum (15-32% over the control), while only Azadirachta indica and Acacia arabica increased the germination in rice ( % over the control). Seedling length was considerably decreased in sorghum due to Syzygium cumini, Tectona grandis and E. tereticornis and in rice due to E. tereticornis and Tamarindus indica. Seedling length was markedly increased in sorghum due to Acacia arabica and in rice due to Azadirachta indica, Samanea saman and Acacia arabica. Leaf extracts from Acacia arabica, Samanea saman and Azadirachta indica at 5 and 10% enhanced vigour index in sorghum, while Acacia arabica and Samanea saman at either concentration increased vigour index in rice. Vigour index was markedly decreased in sorghum due to Eucalyptus tereticornis and Syzygium cumini and in rice due to Syzygium cumini, Tamarindus indica and Eucalyptus tereticornis. Leaf extracts decreased the seedling dry matter in sorghum and rice irrespective of concentrations. Sasikumar et al., (2001) studied the allelopathic effects of leachates of bark, fresh leaves and leaf litter of Eucalyptus tereticornis, E. camaldulensis, E. polycarpa and E. microtheca on the germination, seedling length, dry matter, vigour index and nitrogenase activity of red gram (Cajanus cajan [pigeon pea] cv. CO.5). Bioassay revealed that significant reduction in germination over control in all cases, 7 days after sowing. Dry matter production was affected by E. camaldulensis and E. microtheca. Meanwhile, vigour index was affected by E. camaldulensis, E. polycarpa and E. microtheca. Seedling length was affected in all cases except E. camaldulensis, 37 days after sowing. Simultaneously, reduction in vigour index and nitrogenase activity was also noted in all cases, compared to the control. Sasikumar et al., (2002) studied the allelopathic effects of leachates of bark, fresh leaves and leaf litter of Eucalyptus tereticornis, E. camaldulensis, E. polycarpa and E. microtheca on the germination, seedling length, dry matter, vigour index and nitrogenase activity of black gram (P. mungo 'CO 5'). Bioassay with leachates reduced the germination, whereas, stimulated the dry matter production and vigour index over control at 7 days after sowing. However, the leachates at 37 DAS significantly reduced the seedling length, dry matter production, vigour index and nitrogenase activity, compared to control.

9 Channal et al., (2002a) have studied the effect of aqueous solutions of fresh leaves of seven tree species Syzygium cumini, Acacia arabica [Acacia nilotica], Tamarindus indica, Eucalyptus tereticornis, Tectona grandis, Samanea saman and Azadirachta indica on green gram and pigeon pea. Irrespective of the concentrations in green gram, the percent germination was reduced due to T. grandis (87.25%) and E. tereticornis (90.12%) over the control (91.75%), while it increased with treatment from other tree extracts and was highest (96.75%) with A. indica, followed by A. arabica (95.86%) and T. indica (94.87%). Seedling length decreased compared to the control when treated with extracts of all tree species except S. saman. Leaf extract concentration had no significant effect on germination, seedling length and dry matter except vigour index. Djanaguiraman et al., (2002) studied influence of aqueous leachates of Eucalyptus globulus leaves, with leaf ages (juvenile, mature and senescent) and leachate concentrations (0 (control), 5, 10, and 25%), on green gram, black gram and cowpea. The leaf leachates of E. globulus significantly decreased the germination of black gram, green gram and cowpea as compared to control. Green gram proved most susceptible to the allelopathic effect of E. globulus. Senescent leaves were inhibitorier than the mature or juvenile ones. With the increase in concentration of leaf extract, there was concomitant decrease in germination. E. globulus leachates significantly reduced the root and shoot lengths of green gram, black gram and cowpea than the control. Due to inhibitory effects of the leachates, root growth was much suppressed and maximum inhibition was observed in green gram and the least was observed in cowpea. Similarly, shoot length also showed the identical trend in reduction in green gram and cowpea over the control. Senescent leaves had greater inhibitory effect on the root and shoot growth than mature and juvenile ones. Among the three leachate concentrations used, 25% leachates considerably reduced the root and shoot lengths. The leachates decreased the dry matter in all the test crops and the magnitude of reduction was maximum in green gram, and cowpea was comparatively tolerant to growth suppression by eucalyptus. The allelopathic effect of seven tree leaf extracts, viz. Syzygium cumini, Acacia nilotica, Tectona grandis, Eucalyptus tereticornis, Tamarindus indica, Samanea saman and Azadirachta indica each at 5 and 10% concentration on sunflower and soyabean

10 indicated that germination of sunflower was increased by Tectona grandis, Tamarindus indica and Samanea saman each at 5 and 10% concentration, while it was suppressed by E. tereticornis and Acacia arabica. Soyabean germination was increased by Acacia arabica, Tectona grandis, Samanea saman and Azadirachta indica at both concentrations, while it was decreased by Tamarindus indica. Almost all the leaf extracts enhanced vigour index in sunflower, while only Tectona grandis, Acacia arabica and Azadirachta indica increased the vigour index in soyabean. The seedling dry matter was markedly decreased by Acacia arabica, E. tereticornis, Tamarindus indica and Azadirachta indica in sunflower, while all leaf extracts except E. tereticornis decreased the seedling dry matter of soyabean (Channal et al., 2002b). Devaranavadgi et al., (2003) conducted a study in existing agrosilvicultural systems involving different tree species (Acacia nilotica, Albizia lebbeck, Azadirachta indica, Cassia siamea, Dalbergia sissoo, Hardwickia binata and Leucaena leucocephala), to assess the allelopathic effects of different tree crops on rabi sorghum. The control treatment produced the maximum grain and stover yield. The performance of rabi sorghum in terms of stover and grain yield was inversely proportional to the silvicultural parameters of tree species and as well as the total dry matter produced by them. Germination of sorghum with H. binata was 85% and a similar superiority was observed for root length, shoot length and dry weight of seedlings. Lower values, however, were recorded in Acacia nilotica. The results indicate that among the tree species studied, H. binata had the minimum allelopathic effect on rabi sorghum. To characterize the allelopathic effect of different concentrations (5, 10 and 15%) of neem leaf extract on radish and onion. Gilani et al., (2003) studied the allelopathic effect of Eucalyptus microtheca in a laboratory experiments. The aqueous extracts from different dried plant parts, soaked for 48 hours, inhibited radicle growth, plumule growth and seed germination of Pennisetum glaucum. However, no serious inhibition of seed germination occurred. The toxicity varied from part to part and was related to concentration and soaking duration. Root exudates were highly toxic to the radicle growth followed by leaves, stem and whole plant material. For the growth of plumule, leaves were found to be highly toxic followed by whole plant, roots and stem. Enhancing effect on the growth of radicle was not

11 observed. However, it was observed on the growth of plumule by roots and stem extracts only. Patil et al., (2003) determined the effect of Eucalyptus tereticornis, Casuarina equisetifolia and Tectona grandis on wheat seeds. Eucalyptus showed the highest allelopathic inhibitory effect followed by Tectona grandis and Casuarina equisetifolia. Irrespective of the leachate source, the inhibitory effect on the germination and growth of wheat seedlings increased with an increase in leachate concentration. Agbagwa et al., (2003) studied the effects of different concentrations of Senna alata crude water extracts on the germination, growth and flowering of Celosia argentea. All concentrations of this extract induced a consistent decrease in absolute percentage and rate of germination, and inhibited radical elongation in C. argentea. Earliness in flowering and overall increase in height was obtained from seedlings sprayed with 75 and 100% C crude water extracts. Singh and Singh (2003) studied the aqueous leaf leachates of E. citriodora inhibited the germination and seedling growth of all test crop (Vigna radiata, V. mungo, and Arachis hypogaea). The leachates proved most inhibitory on the germination of A. hypogaea and V. mungo. Thus, the germination of these test crops was more sensitive to the leaf extract than the control. The leaf leachate proved inhibitorier on plumule elongation than on radicle elongation. The magnitude of inhibition on plumule length followed the order: A. hypogaea (100%)>V. mungo (50%)>V. radiata (42.3%) over the control. They concluded that the allelochemicals present in the leaf leachate of E. citriodora had potential to inhibit the physiological processes, i.e. germination, growth, and metabolism of seeds and seedlings of V. radiata, V. mungo and A. hypogaea. Khan et al., (2003) studied the allelopathic effect of soaked, crushedand boiled in tape water Eucalyptus camaldulensis extracts on seed germination and growth of maize var. 'Kissan'. Results showed that all the extracts significantly reduced maize seed germination, root and shoot length, as well as fresh and dry weight. The extracts of boiled eucalyptus decreased seed germination to 66% compared to control with 99% germination. However, the extracts of soaked eucalyptus was the most toxic to root growth and caused higher decrease of maize root length, fresh and dry weight among the 3 extracts. The highest decrease in maize shoot length, shoot fresh and dry weight, was

12 recorded by the extracts of crushed eucalyptus. The suppression of maize seed germination and other growth parameters indicates allelopathic effect. Moradshahi et al., (2003) studied the allelopathic potential of crude volatile oil and aqueous extract of the leaves of Eucalyptus camaldulensis on mitotic index in the root apical meristem of Allium cepa, Hill reaction in isolated spinach (Spinacia oleracea) chloroplast and on radicle growth and peroxidase activity in Lepidium sativa, Echinochloa crus-galli, Avena fatua, Rumex acetosella, Zea mays and Lycopersicon esculentum. The presence of different concentrations of crude volatile oil or aqueous leaf extract decreased the mitotic index. Volatile oil at 0.25 ml/litre and aqueous extract at 50 g/litre decreased the mitotic index and number of cells in prophase, metaphase and anaphase by >97%. Volatile oil and aqueous leaf extract also affected the Hill reaction as evident decrease from to a DCPIP reduction. Aqueous leaf extract at 50 g/litre inhibited the Hill reaction by 88%. Although leaf volatile oil had small effect on peroxidase activity but aqueous leaf extract decreased the enzymic activity significantly. Aqueous extract at 100 g/litre inhibited peroxidase activity in L. sativum by 95% relative to control. Both aqueous leaf extract and crude volatile oil suppressed the radicle growth in all the plant species. Complete inhibition of radicle growth by volatile oil was observed at 2.5 ml/litre. These results suggest that Eucalyptus species suppress the growth of other plant species by affecting several biochemical and physiological processes. Khan et al., (2004) studied the allelopathic potential of leaf extracts (0, 150, 100 and 50 g/litre) of E. camaldulensis on T. aestivum, Avena fatua and Carthamus oxycantha. They reported the germination percentage, seedling length (mm) and biomass (mg) per plant and found C. oxycantha was the most inhibited species while wheat was the most tolerant. Only 20% seed germination was obtained in C. oxycantha compared to the other germination trials when exposed to the E. camaldulensis aqueous extract (150 g/litre). Other concentrations of E. camaldulensis extracts severely inhibited the germination of C. oxycantha. Pawar and Chavan (2004) studied the effects of leaf leachates of Eucalyptus globulus, Moringa oleifera, Melia azedarach, Parthenium hysterophorus and Glycine max on the free proline concentration in the germinating seeds of S. bicolor (cv. M.35-1). S. bicolor seeds were allowed to germinate at 30 o C on filter paper moistened with leaf

13 leachate. Free proline content was analysed in germinating seeds (at 72 h). Leaf leachates from the 5 species significantly increased the free proline content of germinating seeds of S. bicolor. The leaf leachate of E. globulus was highly effective. Prasad (2004) studied the effect of neem (Azadirachta indica), periwinkle (Catharanthus roseus) and carrot weed (Parthenium hysterophorus) leaf extracts at 0, 20, 40, 60, 80 and 100% concentration on plant height, and number of branches and days to flowering on turnip. Low neem rates and moderate periwinkle rates increased plant height and number of branches per plant. Carrot weed showed deleterious effects on the parameters. All three extracts caused delayed flowering. Devaranavadgi et al., (2004) studied the allelopathic effects of different tree crops (Acacia nilotica, Albizia lebbeck, Azadirachta indica, Cassia siamea, Dalbergia sissoo, Hardwickia binata and Leucaena leucocephala) on chickpea. Among the tree species, Hardwickia binata had significantly less allelopathic effect on chickpea when compared to other tree species. The maximum harmful effect was observed with Acacia nilotica. Goetze and Thome (2004) conducted an experiment to analyse the allelopathic effect of Nicotiana tabacum and Eucalyptus grandis on germination and initial development of lettuce, broccoli and cabbage. Extracts were obtained from fresh and dry leaves of tobacco and eucalyptus in 1:4, 1:8 and 1:16 (g/ml) concentrations that were used in germination tests. The extracts reduced germination speed of the three vegetables tested. The extracts obtained from dry leaves, inhibited seed germination. All treatments affected the length of the aerial part and roots, presenting smaller measures compared to the control. All vegetables had the final fresh weight affected by the tobacco extracts. Broccoli showed reduced fresh weight when germinated in extracts supplemented with fresh leaves of eucalyptus. The final number of germinated seeds was affected in almost all treatments, regardless of the type of extract used. Djanaguiraman (2005) studied the leaf leachate (5, 10 and 20%) of Eucalyptus globulus was evaluated for allelopathic effect on rice, sorghum and black gram. Seed germination, shoot length, seedling dry matter and vigour index were significantly reduced by leaf leachate and highest inhibition was observed in 20% concentration. The magnitude of inhibition followed the order of black gram > rice > sorghum.

14 Khan et al., (2005) studied the laboratory experiment to investigate the allelopathic potential of aqueous extracts (150 g/litre each) of Prosopis juliflora and Eucalyptus camaldulensis leaves and Acacia nilotica bark. The germination percentage, seedling length (mm) and biomass yield per plant of Ipomoea spp., Asphodelus tenuifolius, Brassica campestris and Triticum aestivum were significantly affected by the extracts. Eucalyptus camaldulensis and Acacia nilotica had a stimulatory effect on germination percentage of Asphodelus tenuifolius, while Prosopis juliflora and Eucalyptus camaldulensis had inhibitory effect on Brassica campestris. All extracts had inhibitory effects on seedling length of Triticum aestivum and Brassica campestris. Results indicated that Prosopis juliflora and Eucalyptus camaldulensis are more allelopathic than Acacia nilotica. The effect of Acacia nilotica on the test species was comparable with the control, exhibiting its non-inhibitory role in the test species. Species indicated that Ipomoea spp. and Triticum aestivum were less negatively affected than Brassica campestris and Asphodelus tenuifolius. Hence, Prosopis juliflora and Eucalyptus camaldulensis can be exploited as bioherbicides for sustainable weed management. Imtyaz and Chaturvedi (2005) assessed the allelopathic potential of Eucalyptus tereticornis, Azadirachta indica and Albizia procera on wheat, paddy and barley. With different leaf aqueous concentrations (5, 10, 15 %). They found more inhibitory effect on germination of wheat and barley, compared to paddy. Similar trend was observed for seedling growth and dry matter production of all the test crops. Barley was the most inhibited crop and paddy the least by the tested crops. Rios et al., (2005) reported inhibitory effect of Dendrocalamus strictus, Bombosa valguris and Guadua angostifolia on germination of squash (60 %), carrot (70 %), radish (57.5 %) and millet (55 %). Maize and bean germination was not influenced in the study. The strongest allelopathic effect was observed for G. angostifolia and B. valguris. Krishna et al., (2005) studied the influence of allelopathic effects of multipurpose trees, viz., Acacia auriculiformis, Casuarina equisetifolia, Eucalyptus hybrid and Mangifera indica, on the germination behavior, root and shoot growth on some important aromatic and medicinal plants, e.g., kasthuri bendi (Abelmoschus moschatus), sanka pushpa (Clitoria ternatea) and honey plant (Ammi majus). Generally, the adverse effect

15 of the 4 multipurpose trees differed with each medicinal plant. However, maximum adverse effect for the parameters considered was recorded in the M. indica while minimum adverse effects were observed in Eucalyptus hybrid. Sanka pushpa showed the greatest sensitivity compared to the two other species tested. Punjani (2006) studied the allelopathic effect of aqueous leaf extracts (1, 3 and 5 %) of Proposis chilensis (Molina) Stuntz on germination and seedling growth of cotton. The leaf extracts delayed and inhibited the germination and seedling growth of cotton. The higher concentration (5%) proved inhibitor to the germination, seedling length and dry matter as compared to control. Sarkar et al., (2006) studied the allelopathic effect of ripe fruits leachates of soapnut tree (Sapindus trifoliatus L.) on the seed and early seedling biology of sudan grass (Sorghum sudanense) (piper) Stapf. The ripened fruit leachates of soapnut inhibited the germination (%) and its speed. The biochemical parameters like protein, catalase and insoluble sugur content also declined than control, whereas soluble sugar increased with increase in the concentration of leachates. The scanning electron microscopy revealed that the ripened fruit leachates of soapnut had corrosive effect on the seed coat of sudan grass. Shahid et al., (2006) studied the allelopathic effect of different aqueous extracts of plants viz., Sorghum (Sorghum bicolor), Sunflower (Helianthus annuus), johnson grass (Sorghum halepense), viz., (Azadirachta indica), Eucalyptus (Eucalyptus camaldulensis) and acacia (Acacia nilotica) on wheat (Triticum aestivum) and its weeds (Avena fatua, Convolvulus arvensis, Rumex dentatus and Phalaris minor). Germination percentage, shoot length, root length and biomass were significantly inhibited by plant extracts as compared to control with the exception that root length showed stimulatory response to Eucalyptus extract. Sunflower extract was the most inhibiting to germination, shoot and root lengths of wheat and to all species of weeds while application of johnson grass extract resulted in significantly minimum biomass. Wheat was comparatively more tolerant to the extracts tested. Azizi and Fuji (2006) studied the effects of various concentrations of the hydroalcoholic extract of Hypericum perforatum, Salvia officinalis and various concentrations of Eucalyptus oil (Eucalyptus globulus) on the seed germination of A. retroflexus and P.

16 oleraceae. In the second experiment, the effects of various concentrations of Black zira (Bunium persicum) on lettuce and radish seed germination were also investigated. The undiluted extract of Hypericum perforatum and Salvia officinalis had significant inhibitory effects on the germination of A. retroflexus seeds, but not on seed germination in P. oleraceae. Eucalyptus essential oils had strong inhibitory effects on the germination of the seeds of both weed species at 0.7% (v/v). B. persicum essential oils also exhibited inhibitory effects on lettuce and radish seeds. Lettuce seeds were more sensitive than radish seeds to these essential oils. Seed germination in lettuce and radish was completely inhibited at 0.2 and 1.0% (v/v), respectively. The strong inhibitory effects of Eucalyptus and Black Zira essential oils may have promising implications in the organic culture of plants. Ziaebrahimi et al., (2007) evaluate the allelopathic effect of Eucalyptus (leaves extract) on germination and growth of three wheat cultivars and reported the decreased germination percentage, leaf and root lengths, dry and wet weights of both roots and shoots. Activities of peroxidase and polyphenoloxidase as antioxidant enzymes in roots and shoots were also measured. Activity of peroxidases increased in stress conditions and roots showed more increased enzyme activity than leaves. Activity of polyphenoloxidases increased only in one of three cultivars and again roots showed more activity of this enzyme in response to Eucalyptus extract. Ahmed et al., (2007) in a greenhouse experiment evaluated the allelopathic potential of E. camaldulensis on Cicer arietinum, Brassica juncea, Vigna unguiculata, Cucumis sativus and Raphanus sativus growth, using aqueous extracts of fresh leaves. The emergence and growth of all the tested plants were inhibited when grown in the extract-contaminated soil. The inhibitory effects were often found to depend on the concentration and degree of inhibition of the test plant species. The effect was very negligible or sometimes promotory on seedling growth when treated with low concentration of the extracts, and the least affected crops were V. unguiculata and C. sativus. At high concentration, the aqueous leaf extract was highly phytotoxic and significantly reduced the germination and seedling growth of all the test species. These results indicated that these responses were due to an allelopathic effect.

17 Khan and Chaturvedi (2007) studied the effect leaf extracts (5, 10 and 15%) of three tree species, i.e. Eucalyptus (Eucalyptus tereticornis), neem (Azadirachta indica) and safed siris (Albizia procera) on three pulse crops, gram (Cicer arietinum), green gram (Vigna radiata) and black gram (Vigna mungo). The results showed that the gram as most susceptible, while green gram and black gram as tolerant. Neem showed the maximum phytotoxic effect and significantly reduced the germination and growth of the test crops. Ferreira et al., (2007) evaluated the effect of ethanolic extracts of Eucalyptus citriodora and Pinus elliottii on seed germination and initial growth of B. pilosa and lettuce (Lactuca sativa). Five concentrations of each extract (0, 0.25, 0.50, 1.0 and 2.0%) were tested in the laboratory. P. elliottii extract had no effect on B. pilosa and lettuce. However, E. citriodora extract, significantly reduced germination index (GI) of B. pilosa, in all tested concentrations, compared with the control (distilled water). Lettuce GI was affected only by 2.0% concentration of ethanolic extract. Extracts of both P. elliottii and E. citriodora had no significant effect on root length of both B. pilosa and lettuce. Pawar and Chavan (2007) studied the effect of leaf leachates of Eucalyptus globulus, Moringa oleifera, Parthenium hysterophorus and Glycine max on carbohydrate metabolism in germinating seeds of Sorghum bicolor cv. M The leaf leachates of E. globulus, M. oleifera, P. hysterophorus and Glycine max decreased the activity of alpha - amylase and invertase. The leachates also decreased the level of reducing and nonreducing sugars. The leaf leachate of P. hysterophorus caused the maximum disturbance in the carbohydrate metabolism. Khan et al., (2008) studied the allelopathic influence of aqueous extracts of Eucalyptus camaldulensis L. on the germination (%) and seedling growth of wheat. It was noted that aqueous extracts at a concentration of 10, 15 and 20% had inhibitory effect on wheat germination and effect was found significantly higher than the control. Fresh and dry weight of seedling was also reduced significantly over control. The inhibitory effects were increased as the extract concentration increased. They found that wheat sown in fields which had leaf litter of E. camaldulensis L. will be adversely affected the germination, growth and ultimately resulting in lower yields of wheat.

18 Ahmed et al., (2008) studied the allelopathic effects of different doses of Eucalyptus camaldulensis leaf litter on three popular agricultural crops: Falen (Vigna unguiculata), Chickpea (Cicer arietinum), Arhor (Cajanus cajan) and two widely used plantation trees: Sada koroi (Albizia procera) and Ipil ipil (Leucaena leucocephala) were selected as bioassay species. Results suggested that leaf litter of E. camaldulesis induced inhibitory effects. It was also found that the effect depend on concentration of extract and litterfall, type of receiver species. Higher concentration of the materials had the higher effect and vice versa. Though all the bioassay species were suppressed, some of them showed better performance. Vigna unguiculata and Cicer arietinum are recommended in agroforestry based on this experiment. In mixed plantation, Leucaena leucochephala is a better choice while compared to Albizia procera. The responses of Medicago sativa to allelopathic effects of Eucalyptus grandis growing in different soil water conditions was studied by Zhong et al., (2009) using a bioassay method. The effects of leaf extracts were examined on seed germination and seedlings grown in different soil water conditions [75%, 55%, 40%, 30% FC (field water content)]. Regardless of water condition, E. grandis showed an obvious allelopathic effect on M. sativa. Leaf extracts of E. grandis significantly reduced the germination index of M. sativa, and the index was further reduced with a water reduction in soil used to grow E. grandis. E. grandis that grew in the lower soil water conditions (40% and 30% FC) had a higher concentration of leaf extract that significantly inhibited seedling growth in contrast to the lower concentration of leaf extract, which enhanced the seed germination rate of M. sativa. E. grandis that grew in high soil water conditions (75% and 55% FC) produced a low concentration leaf extract that significantly improved seedling growth of M. sativa, while the high concentration extract enhanced the seed germination rate. Higher concentration of leaf extract of E. grandis reduced the leaf chlorophyll content and root activity of M. sativa seedlings. M. sativa showed a relatively strong resistance to E. grandis leaf extracts treatments and could be chosen as a priority species for tree-pasture combinations in E. grandis plantations. The allelopathic effect of the water extract from fresh leaves of 9 agroforestry tree on the germination, seedlings survival, hypocotyl and radicle length and days to first emergence of maize (Zea mays) and sorghum (Sorghum bicolor) was investigated in a

19 growth chamber by Mubarak et al., (2009). Extracts from Ziziphus spina-christi, Sesbania sesban and Tamarindus indica caused a significant reduction in germination of seeds of both crops by 14-71%. Across all the extracts, the germination of seeds and seedlings survival of sorghum was significantly less affected than those of maize. Maximum (compared to the control) survival of maize and sorghum seedlings were obtained in extracts from Khaya senegalensis, Peltophorum pterocarpum, Prosopis africana, Eucalyptus camaldulensis and Spina christi. For both crops, extract from Acacia nilotica imposed the least effect on the hypocotyls length. The same extract significantly increased the radicle length of maize and sorghum seedlings by 47% and 55%, respectively. Extracts forced maize seeds to germinate earlier, while the opposite was observed for sorghum seeds. Fang et al., (2009) studied the influence of aqueous leaf leachate and leaf volatile of Eucalyptus urophylla used to investigate their effect on seed germination and seedling growth of seven native tree species (Cinnamomum burmanni, Cryptocarya concinna, Machilus chinensis, Photinia benthamiana, Pygeum topengii, Diospyros morrisiana and Pterospermum lanceaefolium) and three exotic tree species (Acacia confuse, Albizia lebbeck and Albizia falcataria). It was revealed that aqueous leaf lechate suppressed the seed germination and seedling growth of all the tested species. Allelopathy in pot cultures Sidhu and Hans (1988) studied the effect of litter from E. tereticornis (prepared by chopping 30-cm long shoots from 7-yr-old trees) and incorporated at rates of 0 (control), 1, 3 and 5% into nursery soil in earthen pots. All the plants in pots containing E. tereticornis leaf litter grew significantly less than control plants, with progressive reductions in growth occurring as the per cent of leaf litter increased. The presence of fertilizer made a negligible difference to the results, which are relevant to the use of E. tereticornis in agroforestry systems. Jayakumar and Pannirselvam (1990) in a pot trials with groundnuts and maize, irrigation with 5, 10, 15 or 20% water extracts of abscised leaves of E. globules found that E. globules decreased plant height, leaf area and chlorophyll content compared with

20 plants irrigated with water. Inhibitory effects were more pronounced at higher concentration of the extract. Srinivasan et al., (1990) conducted a pot experiment by growing Vigna mungo, V. radiata, Vigna sinesis, Cajanus cajan and Glycine max for 30 days in topsoil taken under Eucalyptus tereticornis, Casuarina equisetifolia, Leucaena leucocephala and Acacia holosericea. Results showed that topsoil from all 4 tree species reduced crop germination and growth. E. tereticornis had the greatest inhibitory effect. Soyabeans were the most sensitive crop. Soyabean germination in topsoil from under E. tereticornis was 69% of germination when compared to control and DM production was reduced by 10%. Cowpeas were the most tolerant crop. The effect of Eucalyptus on wheat, maize and cowpea, by dibbling the seed of these crops in polybags either unamended, or amended with a layer of fresh leaves, litter or root material from Eucalyptus tereticornis and the polybags filled with soil from an adjoining eucalyptus forest site. Germination of wheat and cowpea was higher in the forest soil than in the field soil, but the reverse was true for maize. Seedling emergence was reduced in all the amendment treatments, and growth parameters were generally reduced in wheat and maize, but not in cowpeas (Blaise et al., 1997). Khan et al., (1999) conducted the pot experiment in which maize cv. Kisan seeds were sown on soil treated with extracts of Eucalyptus camaldulensis or tap water. Eucalyptus extract reduced the germination percentage of maize seed and delayed germination compared with the control. Seedling height and fresh root weight were also reduced, while dry matter production was increased. The extract reduced soil ph but increased Phosphorus content. Patil and Sukanya (2001) studied the polybag experiment to determine the allelopathic effect of Eucalyptus on some legume crops (groundnut, green gram and soyabean). Soil samples along with natural leaf fall from eucalyptus tree row site were collected from 3 m away from the tree row to 18 m distance (6 distance intervals), and 2 kg soil from each distance was put in polybags. Shoot length, root length and shoot dry weight per plant were significantly less in 3 and 6 m distance soils, while root dry weight was reduced up to 9 m distance soil, indicating more adverse effect on the root portion than on the shoot portion. Groundnut shoot length did not change over distances, while

21 that of green gram was adversely affected up to 6 m and that of soyabean up to 3 m. Root growth of all the 3 crops was inhibited in 3 and 6 m distance soils, the greatest reduction being recorded with ground nut. Similar was the case with shoot weight. Patil (2002) studied a greenhouse experiment to determine the allelopathic effect of Eucalyptus site soil on the germination and growth of maize, wheat and sorghum. Soil samples were collected at 3, 6, 9, 12, 15 and 18 m distances from the tree row. Two kg of soil containing natural eucalyptus litter from each distance was placed into the polybags and then watered to bring the soil moisture to field capacity. Ten seeds of each crop were dibbled into the polybags and watered regularly to maintain uniform soil moisture. Twenty one days after sowing, shoot length and dry weight, and root length and dry weight per plant were recorded. The site soil had significant effect on all the parameters studied. The soil collected from 3 and 6 m distances significantly reduced the shoot and root dry weights per plant. The shoot length, and shoot and root dry weights of wheat was the most affected in polybag containing soil collected from 3 m distance. Maize was relatively tolerant to the allelopathic effect of the eucalyptus site soil. Patil et al., (2002) studied the polybag wherein, soil collected near (3 m) the tree row had the maximum inhibitory effect on shoot and root growth, and dry matter accumulation of wheat followed by soil from 6 and 9 m distance. However, the inhibitory effect was not recorded in soil collected from 12 to 18 m distances. Results indicated that the interference of allelochemicals released from decomposing litter present in the soil collected near (3, 6, and 9 m) the tree row and the adverse effect of the Eucalyptus tree was due to both competition for physical resources and inhibitory effects of allelochemicals. Hossain et al., (2002) studied the effects of forest topsoil + leaf litter mixture of four common plantation tree species (Acacia auriculiformis, Artocarpus chaplasha, Dipterocarpus turbinatus and Eucalyptus camaldulensis) on the germination and initial seedling growth of Leucaena leucocephala. The topsoil of adjacent bushy scrub forest area served as control. Highest germination occurred in the topsoil + leaf litter mixture (90:10) of D. turbinatus, whereas, the topsoil + leaf litter mixture of Acacia auriculiformis caused maximum stimulation in the seedling growth and biomass production in L. leucocephala. Mixtures of topsoil + leaf litter mixture (50:50) of E.