Full Text: 1 Introduction Allelopathy is the effect caused by a plant to the surrounding plant either by deteriorating or enhancing its growth depending on its chemical present (Gibson & Liebman, 2003; Mafeo et al., 2010). The performance of seed germination and seedling growth determines the possibility of one plant having an allelopathic effect on another plant by releasing allelochemicals, which thereafter interfere in its physiological development (Nega & Guteda, 2019). The leaves are known to be the most influential source of allelochemicals (Kumar et al., 2006). This allelopathic effect might be positive or negative, it varies with plant species. In agroforestry, the perennial plants play a major role by providing food, fodder, fuel wood, and income by selling the woods, helps to stabilize the environment by providing shade, purify air, control erosion and enhance nutrient cycling (Sobola et al., 2015). However, incorporation of perennial plants in agroforestry could result in unfavourable allelopathic effects on neighbouring plants (Mughal, 2000).  Therefore, assessment of this effect for checking the compatibility of any tree crop is important before establishing any agroforestry systems. Bamboo based agroforestry system plays an important role in enhancing food productivity, diminished the exploitation of important timbers, provide household income and a suitable resource for biofuels (Chin et al., 2017; Akoto et al., 2018). Bamboo being fast-growing, renewable versatile plant and the fast regrowth characteristics has proved to sequester more CO₂ in a short period (Ahlawat, 2014), thus help mitigate climate change. However, the rate of carbon sequestration depends upon the age and species composition, silviculture practices, and land use system and environmental factors (Partey et al., 2017). It also enhances the degraded soil and advances the economics of developing tropical nations by securing foods (Kittur et al., 2016). D. longispathus is a clump-forming bamboo and characterized by thick culm wall (12mm) and is grown naturally in the forests of North East India (Banik, 2015). It is widely found in India, Bangladesh, Myanmar and Thailand (Barooah & Borthakur, 2003). S.dullooa has thin culm wall and is dominant bamboo species that forms the most important vegetation in the place they grow both in tropical and subtropical hills (Nath & Das, 2010).  However, there is a need to test their compatibility with associate crops for its phytotoxic effect before recommending to be a suitable crop combination for bamboo-based agroforestry systems. Therefore, the current study aims to understand the allelopathic effect of D. longispathus and S. dullooa on maize and soyabean (local variety) crop based agroforestry systems. Further, effect of these two bamboo species on germination and growth behaviour of maize and soyabean crop was also evaluated during the study. 2 Materials and Methods 2.1 Experimental Setup The study was carried out in the Forestry Department, Mizoram University, Tanhril, Aizawl (23°44'05.5" N latitude, 92°40'25.0" E longitude; 795 meters above sea level). Naturally shed leaves of two bamboo plant species i.e. D. longispathus and S. dullooa approximately 5 years of age were collected from Forest Research Centre for Bamboo and Rattan located at Bethlehem Vengthlang, Aizawl, Mizoram. The collected leaves were kept for air drying for two weeks. After drying, leaves were wiped with cloth and ground to powder with the help of grinder and passed through 0.5mm mesh sieve. The sieve samples were stored in air-tight polythene bags for use in extract preparation. The aqueous extract was prepared separately for both the selected bamboo species by adding 100 gram ground leaves to 1000 ml of distilled water which made up the ratio of 1:10 (w/v), mixed thoroughly. After 24 hours of keeping at room temperature, the extracts were obtained by filtering the solutions with Whatman filter paper No. 1.  Different concentrations were made by diluting the stock solution with distilled water viz., 5%, 10%, 15%, 20%, and 25% respectively. Before use, surface sterilization of the maize and soyabean seeds was done by sodium hypochlorite (0.1%) for two minutes followed by rinsing with tap water. Twenty treated seeds of each food crops were kept in Petri-plates after sterilizing (hot air oven at 120⁰C) containing the filter paper and saturated with respective concentration except control treatment (with distilled water). Seed germination, shoot and root extension were measured and recorded after 21 days of sowing. In the case of poly pot experiment, the ground leaves (henceforth, will be termed as leaf extract) were thoroughly mixed with 5 kg of soil per pot and different treatments were prepared viz., 5g+soil, 10g+soil, 15g+soil, 20g+soil, 25g+soil, for both the bamboo species. Soil without amendment with grounded leaf was taken as control. Ten seeds each of maize and soyabean were sown in each poly pot and irrigated with water. At 3-4 leaf stage after germination, the best performing plant was selected and retained while others were removed from the polypot. Germination percentage and other growth parameters were recorded after two months of sowing. The following formulae were used for obtaining percentage of germination and inhibition or stimulation (Surendra & Pota, 1978): GP (Germination percent)=
                                        Seed germinated/Total seeds sown × 100 Inhibition or Stimulation Percentage =
                  [(Control value- Treatment value)/control value] × 100. 2.2 Statistical analysis Data were subjected to analysis of variance and the mean values were compared using Duncan’s Multiple Range Test at 5% and 1% probability level. Statistical analysis was done using SPSS version 20. 3 Results and discussions 3.1 Bioassay 3.1.1 Germination The aqueous leaf extracts of D. longispathus and S. dullooa were found to stimulate the germination percentage of maize with increased concentration which was recorded 96.67% and 93.33% at 15% concentration of D. Longispathus and S. Dullooa respectively, however this difference was not found significant (p≤0.05). On the other hand, both the bamboo species inhibited the germination rate of soyabean seed which was recorded highest at 10% (83.33%) and 25% (88.33%) concentrations respectively (Table 1). This finding agreed with Abugre et al. (2011), where the root extract of Sennasiamea increased the germination of Zea mays and Lycopersicon esculentum. Further, Suseelamma & Venkata (1994) stated that the inhibition of germination might be the resultant effect of allelochemicals that are water-soluble entering into the seed, which retard germination and growth. The findings also conform to the report of Nega & Gudeta (2019) where aqueous extracts of Eucalyptus globules inhibited the germination and seedling growth of highland teff and barley at different concentrations. 3.1.2 Root and Shoot Elongation The extracts of D. longispathus stimulated maize root and shoot elongation whereas highest stimulatory effect on root length (+26.47%) and shoot length (+144.50%) was observed at 25% concentration of D. longispathus (Table 2), these findings are in agreement with the results of Stachon & Zimdahl (1980) and Rejila & Vijayakumar (2011). The study revealed that the root length of soyabean is less affected at the higher concentration of D. longispathus leaf extracts, thereby showing the highest significant stimulatory effect at 25% (+19.96%). The above finding is in agreement of the result of Lalremsang et al. (2017) where lateral roots of maize showed stimulatory effect at higher concentration of Schimawallichi and Mesuaferrea leaf extracts when compared to control in a pot experiment.  Similar to D. longispathus, the highest concentration (25%) of S. Dullooa leaf extracts also had a stimulatory effect on root length of maize (+6.28%) for S. Dullooa, however, the leaf extract of the same species showed inhibitory effect on shoot length of maize, the highest being at 10% concentration (-37.36%) (Table 2). The results of Saboya & Borghetti (2012) are in agreement with the results of the present study where seedling’s mean root length of Copaifera langsdorffii and Dioscorea alata were enhanced by four times compared to mean shoot length. However, the aqueous leaf extracts of S. dullooa showed an inhibitory effect on the root and shoot length of soyabean. The highest inhibition was observed at 15% (-14.79%) and 5% (-29.07%) concentrations for root and shoot respectively (Table 2). This might be due to the interference of phytohormones of the food crops by chemicals present in the extract (Cheng & Cheng, 2016). This finding is also at par with the findings by Jash et al. (2019) where Chromolaena adolata significantly reduces the grass pea’s root and shoot length as well as its biomass in the bioassay experiment.  3.2 Pot culture 3.2.1 Germination percentage All treatments of D. longispathus extract except 20g+soil inhibited seed germination in maize when compared to control. Similar to maize, it also had an inhibitory effect on the soyabean seed germination and among the tested treatments 20g+soil and 25g+soil had higher seed germination than the control (Table 1). These findings are similar to the findings of Rafigul Hoque et al. (2003), where the germination rate of Brassica juncea, Phaseolus mungo, Raphanus sativus, Vigna unguilata, and Cicer arietinum were inhibited highly with increase of extract concentration in Acacia auriculiformis. These results are in agreement with the findings of Thakur et al. (2017) those who reported inhibitory effect of Melia dubia leaf extracts and litter on germination and growth of green gram and black chickpea. Further, S. dullooa leaf extracts reduced seed germination in both maize and soyabean crop. The inhibitory effect was concentration-dependent. Maximum inhibitory effect was observed at 25g+soil for both maize and soyabean when compared to control (Table 1). These findings are similar to findings reported by Mandal et al. (2016), Wu et al. (2015), Nath et al. (2016), where inhibition may be caused by occurrence of nutrients, growth regulators, alkaloids and toxins in the leaf leachates that causes retardation of seed germination and seedling growth.  3.2.2 Root and shoot elongation The leaf extracts of D. longispathus showed stimulatory effect with increased in concentration for both root and shoot length of maize, wherein significant stimulatory effect for shoot length was observed at 25g+soil (+28.64%). However, D. Longispathus extracts had retarding effect on the root as well as shoot length of soyabean and this effect was found concentration dependent. The maximum inhibition was observed at 20g+soil (-10.66%) and 25g+soil (-8.28%) for root as well as shoot length respectively (Table 3). The above results conform to the result given by Salama & Rabiah (2015) where the low concentrations of aqueous extract of C. colocynthis had a stimulatory effect while higher concentration induced greater inhibition on root and shoot length of Hordeum vulgare. Like D. Longispathus, the leaf extract of S. dullooa also had an inhibitory effect of the root length of maize and maximum root inhibition was reported at the highest concentration of S. dullooa while in case of shoot length it showed concentration dependent effect. The highest stimulatory effect for root length was observed at the lowest concentration (+34.43%) which was followed by 20g+soil (+29.96) (Table 3). Results are in agreement with the findings of Sisodia & Siddiqui (2010), who reported reduction in radical, plumule length and dry weight of test seedlings with Croton bonplandianum extracts application. Altering the pH and osmotic potential of extracts causes inhibitory effects (Sisodia & Siddiqui 2008). In soyabean, the root length growth was highly affected by the leaf extracts of S. dullooa. The maximum inhibitory effect on root growth was observed at 5g+soil (-4.45%) and 20g+soil concentration of S. dullooa (-9.01%). These results confirm the findings of Barkosky & Einhellig (2003), where seedlings growth of soyabean was reduced with increasing concentrations of hydroxy benzoic acid (allelochemicals) under greenhouse condition. Similar findings had been observed by Kumar et al. (2019) on wheat by Anthocephalus cadamba and Melia dubia leaf extracts.  3.2.2 Biomass The study showed that extracts of D. longispathus inhibit the dry root weight of maize in all the treatments when compared to control (Table 4). Similar to these results, Namkeleja et al. (2013) also reported that the A. mexicana seed and leaf extracts reduced both the fresh and dry weight of B. dictyoneura as concentration increased. This may be due to the presence of allelochemicals that inhibit the synthesis of protein along with carbohydrates, thereby growth inhibited. In soyabean, the dry weight of root and shoot increased amid high extract concentration compared to control. The highest shoot biomass was observed at 10g+soil (+23.40%) and 25g+soil tretments (+10.63%) (Table 4). A similar result was observed by Khan et al. (2007), who reported that Eucalyptus extracts had a stimulatory effect on dry root and shoot weight of maize which may be due to its oil having antiseptic properties that might help in increase root, shoot length and weight. Further, similar results were observed by Lalremsang et al. (2018) where the aqueous leaf extracts of Flemingia semialata showed a stimulatory effect on the biomass of maize. The leaf extract of S. dullooa exhibited a higher inhibitory effect on root dry weight than shoot dry weight of maize where the highest reduction of root dry mass was observed at 10g+soil and 20g+soil treatments (-22.91%) (Table 5). Similar results were reported by Namkeleja et al. (2013), these researchers evaluated the allelopathic effect of Argemone mexicana on roots and shoot dry  weight of Brachiaria dictyoneura and Clitoria ternatea and found that root growth was severely affected than shoot growth. On the contrary, enhanced root and shoot dry weight of soyabean was recorded at high concentration. The highest stimulatory effects of root (+ 60.00%) and shoot (+101.89%) biomass were observed in the treatment with 25g+soil (Table 5). The above results were at par with the findings of Wu et al. (2015) who reported that extracts of Mikania micrantha promoted the dry weight of shoot, root as well as leaf area of test crops. 3.2.4 Collar diameter and number of leaves The leaf extracts of D. longispathus showed an inhibitory effect on the collar diameter of maize and soyabean crops. The highest inhibition on collar diameter was observed at lower concentration (5g+soil) for maize and for soyabean at 15g+soil while the highest concentration (25g+soil) of D. longispathus had stimulatory effect on the collar diameter of maize. In the case of soyabean the highest enhancement in collar diameter was observed at a lower concentration of 10g+soil (Figure 1). Maximum number of leaves was recorded in lower concentrations than the higher concentration of extracts in both the test crops (Figure 2). Previous research of Ahmed et al. (2018) also gave similar results on these aspects who concluded that the leaf litter of E. camaldulensis negatively reduced the collar diameters and leaf number with increasing concentration of leaf litter. Similarly, leaf extracts of S. dullooa prominently reduced the collar diameter. The highest inhibitory effects were observed at 10g+soil and 20g+soil concentration in maize and soyabean respectively (Figure 1). The number of leaves was found to be increased in all concentrations of extracts when compared to control (Figure 2). These observations agreed with the findings of Adetayo et al. (2005) and Abu-Romman (2011), who suggested that leaf number, was significantly influenced by the allelochemicals of Chromolaena odorata and Achillea biebersteinii. Kumar et al. (2018) also reported reduce collar diameter of maize with the application of Melia dubia leaf extracts.  Conclusions The results of the experiment revealed that the leaf extracts of D. longispathus and S. dullooa had pronounced effect on soyabean in terms of germination percent, and growth parameters compared to maize crops. It can also be concluded from the study that S. dullooa leaf extracts has a higher inhibitory effect than the D. longispathus on the test crops. The allelochemicals from bamboo leaves influenced the germination percent, growth parameters differently on the same crop. Therefore, there is a need to determine the types of allelochemicals present in the bamboo species which might have regulated the stimulatory as well as inhibitory effects on the test crops before recommending the two bamboo species as potential woody perennial to be used in agroforestry systems.  Acknowledgements The authors are grateful to the members of the Forest Research Centre for Bamboo and Rattan, Bethlehem Aizawl, Mizoram for allowing the collection of bamboo leaves and also to the Head, Department of Forestry for permitting us to use the necessary instruments required for the completion of the research work. Thanks are also to Dr. J.K. Chaudhary, Department of Animal Breeding and Genetics, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Selesih for his help in analysing the data with statistical softwares. Conflict of Interest The authors declare that there is no conflict of interest.