sustainability

Article Potential Allelopathic Candidates for Land Use and Possible Sustainable Weed Management in South Asian Ecosystem

Kohinoor Begum 1 , Mashura Shammi 2 , Nazmul Hasan 3 , Md. Asaduzzaman 4 , Kwame Sarpong Appiah 1 and Yoshiharu FUJII 1,*

1 Department of Biological Production Science, United Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan; [email protected] (K.B.); [email protected] (K.S.A.) 2 Department of Environmental Science, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh; [email protected] 3 Fruit Science Laboratory, Department of Biological Resource Science, Faculty of Agriculture, Saga University, Saga 840-0027, Japan; [email protected] 4 Hajee Mohammad Danesh Science and Technology University, Dinajpur 5200, Bangladesh; [email protected] * Correspondence: [email protected]



Received: 29 March 2019; Accepted: 3 May 2019; Published: 9 May 2019


Abstract: Weed management is one of the significant challenges of field crops since weeds pose a remarkable threat to crop productivity in South Asian countries, including Bangladesh. Allelopathy, a phenomenon whereby secondary metabolites produced and released by one plant species influence the growth and development of other species can be exploited in sustainable management. The focus of this study was to evaluate potential allelopathic plant species which can be further explored as alternatives to synthetic herbicides or incorporated as part of integrated weed management in sustainable agriculture. Two hundred fifty-two plant samples from 70 families were collected from Bangladesh and evaluated with the sandwich bioassay. Thirty-one percent of the samples showed significant allelopathic potential on lettuce radicle elongation. Among the species that showed substantial inhibition, more than 7% of the samples showed higher inhibition (HI) and 25% showed moderate inhibition (MI) on lettuce radicle. Fruit pulps of Couroupita guianensis (95.4%), fruits of Phyllanthus emblica (95.4%), and Acacia concinna (95.4%) showed the highest inhibition on lettuce radicle elongation. In contrast, the leaf of Bombax insigne had growth promoting activity by stimulating radicle (23%) and hypocotyl (80%) elongation of lettuce seedlings. This result suggested that the species with significant plant growth inhibitory potential may play a vital role as an alternative to the increasing use of synthetic herbicides for sustainable weed management in agricultural land.

Keywords: allelopathy; sandwich bioassay; natural weed management; growth inhibition; agro- ecology; sustainability

1. Introduction Bangladesh, along with the other agriculture-dominated developing countries in the world, is addressing alarming problems of crop production because of the excessive application of agro-chemicals in agricultural land. Additionally, weeds, diseases, and pests are also critical issues of crop cultivation that negatively affect crop productivity. The consequence is the misapplication of several classified hazardous, persistent organic pollutants (POPs), pesticides, fungicides and weedicides [1], which has resulted in the potential contamination of water, soil, and food threatening environmental safety [2,3].

Sustainability 2019, 11, 2649; doi:10.3390/su11092649 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 2649 2 of 18

Moreover, there is a lack of advanced knowledge in farm management practices in the agricultural sector in Bangladesh [4]. In addition to the problems associated with the misapplication of agro-chemicals, Bangladesh is densely populated with an increasing population [5,6]. It has been estimated that the population of Bangladesh would be approximately 215.45 million by 2061 under high-variant fertility assumption, which is about 56.6% higher than the present situation [5]. However, agriculture employs about 47.5% of the population in Bangladesh with 70% deriving their livelihood from agriculture [7]. In order to ensure food safety for the huge population, there is a need to adopt strategies that would optimize the productivity of agricultural lands in Bangladesh. According to the report of Oerke, potential yield losses by weeds are 37% in rice, 23% in wheat, 37% in soybeans, 40% in maize, 36% in cotton, and 30% in potatoes [8]. Weeds have indeed become the primary concern of farmers resulting in billions of dollars of yield loss [9]. Before the 1960s, the application of pesticides in field crop was virtually insignificant in Bangladesh. As a result of various government schemes that favor the use of agro-chemicals, the application of pesticides has increased dramatically over the past four decades [10–13]. Moreover, the indiscriminate use of synthetic pesticides, including herbicides, has created resistance capacity in the weed species, that might be a notable threat for the field ecosystem [14,15]. Allelopathy can be a comprehensive alternative approach to sustainable weed management in agriculture [16]. To explore the allelopathy of Bangladeshi plant species (medicinal and non-medicinal), there is a need to evaluate plant species for potential allelopathic species and their corresponding allelochemicals. Allelochemicals that are released to the environment through different routes, such as leaching, volatilization, root exudation, and decomposition of plant residues, have been well studied [17,18]. Some of the screened plant samples of this study have plant and weed suppression ability. HeIianthus annuus suppressed Abutilon theophrasti, Datura stramonium, Ipomoea purpurea, and additionally Brassica kaber [19,20]. Leaf extract of Psidium cattleianum and Cymbopogon flexuosus affected seed germination and early seed development of Zea mays and Raphanus sativus [21]. Aqueous extract of cinnamon (Cinnamomum verum), showed decreasing germination potential (86.3%) on lettuce seeds [22]. Aqueous extract of Syzygium aromaticum with eugenol as the major component, [23] inhibited seed germination of lettuce (70–100%) and tomato (60–100%) at the concentration of 7.75 mg/mL [24]. Eight and ten percent aqueous extracts of dry leaves of Ficus bengalensis, Azadirachta indica, Melia azedarach, Mangifera indica, and Syzygium cumini significantly reduced the seeds germination of parthenium in laboratory bioassays. Ficus bengalensis and Mangifera indica were found to be the most inhibitory to radicle and plumule growth of parthenium [25]. The germination of Hibiscus esculentus was reduced by 30% when treated with aqueous root extracts of Azadirachta indica, and it increased up to 43.3% with 2% aqueous leaf extract [26]. Seed kernel aqueous extracts of A. indica and Melia azedarach had more pronounced adverse effects on wheat and rice but in contrast, weed (E. crus-galli, Medicago hispida, and Phalaris minor) germination was less adversely affected compared to extracts from leaf and seed coat [27]. Hazra and Tripathi [28] reported that under semi-arid conditions, forage yield of oats (Avena sativa) was 26% less under neem (A. indica) tree than in open plots. The aqueous extracts of wood apple fruit (Aegle marmelos) and leaves perhaps are the most promising and received attention at least partly owing to the presence of growth inhibitory compound. The crude extracts had a herbicidal effect on spiny amaranth, barnyard grass, and green amaranth seeds [29]. Aqueous extracts and leachates of fresh leaves and the litter of Eupatorium riparium suppressed germination and radicle and plumule growth of Galin-soga ciliate and G. parviflora, Eucalyptus odorata extracts reduced the germination of the seeds of spinach, Chinese cabbage, rape and Capsicum frutescens [30,31]. In contrast, the mechanism of the inhibitory effect of allelochemicals acts as promotor by the termination of cell division, plant hormones assembly, protein synthesis, enzyme activities, membrane permeability, proper mineral uptake, pigment synthesis, photosynthesis, respiration, movement of stomata, and nitrogen fixation [32–34]. The sandwich bioassay method adopted in this study is an efficient tool for screening the allelopathic effect of leachate under laboratory conditions on a large scale. Besides, the dynamics of Sustainability 2019, 11, x FOR PEER REVIEW 3 of 18

SustainabilityThe 2019sandwich, 11, 2649 bioassay method adopted in this study is an efficient tool for screening3 of 18 the allelopathic effect of leachate under laboratory conditions on a large scale. Besides, the dynamics of the environmental factors may be relatively manipulated to hold some bioassay characteristics (like the environmental factors may be relatively manipulated to hold some bioassay characteristics (like physical, chemical, and biological) on field condition. This bioassay methodology has been explored physical, chemical, and biological) on field condition. This bioassay methodology has been explored in in the identification of several allelopathic plants. It may draw attention to the effects of natural the identification of several allelopathic plants. It may draw attention to the effects of natural herbicides herbicides on farming to promote sustainable agriculture practices. on farming to promote sustainable agriculture practices. Given this context, the present study attempted to identify (a) the potential allelopathic species Given this context, the present study attempted to identify (a) the potential allelopathic species from Bangladesh (b) and examine the prospect of significant allelochemical isolating candidates as a from Bangladesh (b) and examine the prospect of significant allelochemical isolating candidates as future scope. In this study, a total of 252 plant samples from Bangladesh were evaluated to select a future scope. In this study, a total of 252 plant samples from Bangladesh were evaluated to select promising allelopathic species through sandwich bioassay. promising allelopathic species through sandwich bioassay. 2. Materials and Methods 2. Materials and Methods

2.1.2.1. Study Study Area Area TheThe plant plant samples samples were were collected collected from from the the South South Asian Asian country, country, Bangladesh, Bangladesh situated, situated between between 24°00′ north latitude and 90°00′ east longitude. The major neighboring country is India all around 24◦000 north latitude and 90◦000 east longitude. The major neighboring country is India all around and in the southwest region, Myanmar. The capital city, Dhaka, is situated at 23°51′ north latitude and in the southwest region, Myanmar. The capital city, Dhaka, is situated at 23◦510 north latitude and 90°24′ east longitude. Chittagong is another major city in a hilly area of Bangladesh located at and 90◦240 east longitude. Chittagong is another major city in a hilly area of Bangladesh located at 22°21′ north and 91°50′ east coordination. The Tropic of Cancer line passes through the country and 22◦210 north and 91◦500 east coordination. The Tropic of Cancer line passes through the country and touchestouches Dhaka, Dhaka, Khulna Khulna and and Chittagong Chittagong divisions, divisions and, thusand the thus climate the climate of the territory of the territory becomes be mainlycomes subtropical.mainly subtropical. Though it Though is a sub-tropical it is a sub country,-tropical the couareantry, accomplishes the area accomplisheswith the diverse with plant the species. diverse Twoplant hundred species. fifty-two Two hundred samples fifty were-two collected samples from were diff collectederent places from of thedifferent country places (Figure of 1the). country (Figure 1)

Figure 1. Samples collection locations in Bangladesh (1. Dhaka National Botanic Garden, Dhaka— DNBG,Figure 2. 1. Sher-e-Bangla Samples collection Agriculture locations University, in Bangladesh Dhaka—SAU, (1. Dhaka 3. Bangladesh National Botanic Agriculture Garden, University, Dhaka— Mymensingh—BAU,DNBG, 2. Sher-e- 4.Bangla Chittagong Agriculture University, University, Chittagong—CU, Dhaka— 5.SAU, Jahangirnagar 3. Bangladesh University, Agriculture Savar, Dhaka—JU,University, 6. Mymensingh The local market,—BAU, Dhaka—LM). 4. Chittagong University, Chittagong—CU, 5. Jahangirnagar 2.2. PlantUniversity, Samples Savar, and Preparation Dhaka—JU, 6. The local market, Dhaka—LM).

2.2.The Plant sample Samples plant and parts Preparation were freshly collected from the spots to evaluate the allelopathic potentiality of the different plant species. The samples were packed in separate paper bags and dried in the sun for 72 h. Then each sample was kept in an air-tight zip-lock paper bag separately for further use. A thick, Sustainability 2019, 11, x FOR PEER REVIEW 4 of 18

SustainabilityThe 2019 sample, 11, 2649 plant parts were freshly collected from the spots to evaluate the allelopathic4 of 18 potentiality of the different plant species. The samples were packed in separate paper bags and dried in the sun for 72 h. Then each sample was kept in an air-tight zip-lock paper bag separately unscentedfor further tissue use. was A thick locked, unscented inside each tissue bag to was absorb locked the inside unwanted each moisture bag to absorb trapped the inside. unwanted These samplesmoisture were trapped sent to inside. the Department These samples of Biological were sent Production to the Department Science, Laboratory of Biological of International Production Agro-BiologicalScience, Laborator Resourcesy of International and Allelopathy, Agro-Biological Tokyo University Resources of and Agriculture Allelopathy, and Technology,Tokyo University Japan forof conductingAgriculture theand study.Technology, The majorityJapan for ofconducting the plant the samples study. wereThe majority collected of fromthe plant the Nationalsamples Botanicwere collected Garden, from Mirpur, the National Dhaka (DNBG), Botanic Gar 44%,den, followed Mirpur, byDhaka Sher-e-Bangla (DNBG), 44%, Agriculture followed University,by Sher-e- Dhaka—(SAU)Bangla Agriculture and ChittagongUniversity, University,Dhaka—(SAU) Chittagong—(CU), and Chittagong 19%,University, Localmarket, Chittagong Dhaka—LM,—(CU), 19% 7%,, BangladeshLocal market, Agriculture Dhaka—LM, University, 7%, Bangladesh Mymensingh—(BAU), Agriculture University, 6%. Jahangirnagar Mymensingh University,—(BAU), Savar, 6%. Dhaka—(JU),Jahangirnagar 5%. University, Savar, Dhaka—(JU), 5%.

2.3.2.3. Sandwich Sandwich Method Method TheThe sandwich sandwich method method [ 35[35]] was was adoptedadopted toto determinedetermine thethe allelopathy due to leachates from from the the selectedselected plant plant samples samples in in the the laboratory laboratory condition condition (Figure (Figure2). 2 All). All the the plant plant samples samples were were screened screened out byout this by method this method using using a six-well a six plastic-well plastic dish. The dish. dimension The dimens of eachion of well each was well 36 mmwas 3618 mm mm. × 18 Various mm. × amountsVarious ofamounts dry plant of dry materials plant materials (10 mg and (10 50mg mg) and and 50 mg) 10 mL and of 10 0.75% mL of autoclaved 0.75% autoclaved agar was agar set was as a sandwichset as a sandwich pattern. The pattern. amount The of amount (10 or 50)of (10 mg or per 50) well mg (10 per cm well2) considered (10 cm2) considered based on the based estimation on the ofestimation average fallen of average leaves falle aboutn leaves 3–5 tons about per ha3–5 per tons year per [ 35ha]. per Only year the [35 autoclaved]. Only the agar autoclaved without plantagar materialwithout in plant multiple material dishes in wasmultiple used dishes as a control. was used Five as lettuce a control. seeds Five (Lactuca lettuce sativa seedsvar. (Lactuca legesse, sativa Takii Seedvar. Co.,legesse, Ltd., Takii Kyoto, Seed Japan) Co., Ltd. used, Kyoto, as receptor Japan) plants,used as were receptor placed plants, at the were top ofplaced the agar at the layer. top Dishesof the wereagar appropriately layer. Dishes sealedwere appropriately by cellophane sealed tape toby avoid cellophane external tape contamination to avoid external or gaseous contamination interaction. or Thegaseous dishes interaction. were wrapped The indishes aluminum were wrapped foils to prohibit in aluminum the light foils interaction to prohibit and the incubated light interaction for three days and atincubated 25 ◦C in the for incubator three days (NTS at Model 25 °C MI—25S). in the incubator Each of the (NTS experiments Model MI was—25S). replicated Each at of least the threeexperiment times. s was replicated at least three times.

Additional 5 ml agar/well

Six-wells * A (10 mg) 4th step multiple 1st step * B (50 mg) plastic dish Placing lettuce seeds at the top Adding 5 ml Plant dry agar layer 2nd step agar/well samples/well 3rd step

FigureFigure 2. 2.Sandwich Sandwich method method [35 [35]], first, first step step to theto the fourth fourth step, step, condition condition with with 0.75% 0.75%w/v autoclavedw/v autoclaved agar foragar sandwich for sandwich layers, layers, oven dried oven plant dried materials plant materials (10 mg and(10 mg 50 mg), and five50 mg), lettuce five seeds lettuce (Lactuca seedssativa (Lactucavar. legesse,sativa v Takiiar. legesse, Seed Co., Takii Ltd., Seed Kyoto, Co., Ltd. Japan), Kyoto, placed Japan vertically.) placed vertically.

2.4.2.4. Analytical Analytical Study Study TheThe experimental experimental design design of of this this study study was was set set up up as aas completely a completely randomized randomized design design (CRD) (CRD) with ninewith replications. nine replications. The statistical The statistical analysis analysis was done was by done the evaluation by the evaluation of means of (M), means standard (M),deviations standard (SD),deviations and standard (SD), and deviations standard variances deviations (SDV) variances using (SDV) Microsoft using O Micrfficeosoft program Office 2016. program The criterion 2016. The of thecriterion standard of deviationthe standard variance deviation (SDV) variance estimated (SDV) the range estimated of significant the range effects of ofsignificant the species. effects Criteria of indices:the species. * = M Criteria+ 0.5 (SD), indices ** = M: * += M1 (SD), + 0.5 *** (SD),= M **+ =1.5 M (SD),+ 1 (SD) ****, =***M = +M2 + (SD) 1.5 indicate(SD), **** the = M radicle + 2 (SD) and hypocotylindicate the inhibition radicle rate.and hypocotyl inhibition rate. TheThe allelopathic allelopathic potentiality potentiality waswas evaluatedevaluated byby comparingcomparing the differences differences of the inhibitions of of radiclesradicles and and hypocotyls hypocotyls of of the the test test plants plants (Lactuca (Lactuca sativa sativa) grown) grown on agar on agar sandwich sandwich without without dried dried plant samplesplant samples and the and treatments the treatments with dried with plantdried samples plant samples. using Equations (1) and (2) below [18,36].

(Av. L. o f Tr / H) x 100 E or Gr % = (1) Av. L o f Cr / H Sustainability 2019, 11, 2649 5 of 18

(E : Elongation, Gr : Growth rate, Av : Average, L : Length, Tr : Treatment radicle,

Cr : Control radicle, H : Hypocotyl

I% = 100 E or Gr % (2) − (Inhibition : I, Elongation : E, Growth rate : Gr)

3. Results

3.1. Allelopathic Effect: Inhibition Diversity among the Plant Species The inhibition diversity was evaluated based on the allelopathic effect of the leachates of the different plant parts on lettuce seedlings. Inhibition evaluation was done for all the 252 plant samples (Table1) according to di fferent plant species under different plant families. The inhibition percentage range on lettuce radicles and hypocotyls was 23.1 to 95.4 % and 150 to 80.0%, respectively, when − − treated with 10 mg. Whereas the range became 0.92 to 100%, 121 to 100% by the treatment of 50 mg − dry plant sample. The inhibition of lettuce radicle varied more than the hypocotyls. Among the 252 plant samples, 81 showed potential radicle inhibition under 10 mg dry plant sample treatment evaluated by standard deviation variance (SDV). Among samples that showed potential inhibition of lettuce radicle, more than 17 samples (6% of total samples) showed higher inhibitory activity (HIA) that ranged from 76.9 to 95.4%., 63 samples (25% of total samples) showed moderate inhibitory activity (MIA) with 53.6–76.5% inhibition range. One hundred seventy-two samples (67% of total samples) showed lower inhibition activity (LIA) by the evaluation of the sandwich method. Among all evaluated plant samples, the highest plant species were examined from the family of Fabaceae (18 species), Asteraceae (17 species), Acanthaceae and Apocynaceae (12 species), Euphorbiaceae and Lamiaceae (10 species), Rutaceae (9 species), Malvaceae (7 species), Rubiaceae (7 species), and some other following species under different families also evaluated. Among the 252 plant samples the fruit pulp of Couroupita guianensis (Lecythidaceae), fruit of Phyllanthus emblica (Phyllanthaceae), and fruit (pod) of Acacia concinna (Fabaceae) showed most robust radicle inhibition value of 95.4% with 10 mg dry sample. Whereas under 50 mg treatment these three species showed 98% inhibition state. The ± correlation between the inhibition percentages of radicle and hypocotyl of the samples revealed that the allelochemicals inhibition affects radicles more than the hypocotyls for both 10 mg and 50 mg dried plant matters.

Table 1. The radicle and hypocotyl inhibition percentage of lettuce seedlings in sandwich method agar gel containing 10 mg plant dry materials.

Dry Samples Content Site (10 mL Agar 1) Score Family Botanical Name Plant Part − Code 10 mg 50 mg R% H% R% H% Acanthaceae 1 Rungia pectinate Leaf 78.3 27.2 77.1 4.67 ** * − − Acanthaceae 4 Justicia adhatoda Leaf 76.4 11.4 82.8 44.5 ** − Acanthaceae 4 Asystasia gangetica Leaf 72.7 19.0 17.0 66.4 ** − − Acanthaceae 3 Phaulopsis imbricate Leaf 67.7 12.6 75.7 17.7 ** − Acanthaceae 5 Adhatoda vasica Leaf 56.7 10.4 71.5 44.9 * Acanthaceae 3 Nelsonia canescens Leaf 50.0 78.8 63.7 16.0 - − Acanthaceae 1 Justicia gendarussa Leaf 45.5 8.69 62.3 14.4 - Acanthaceae 1 Justicia peruviana Leaf 34.5 13.0 68.7 46.2 - Acanthaceae 3 Justicia peruviana Stem 30.9 48.5 80.7 17.3 - − Acanthaceae 4 Acanthus ilicifolius Leaf 27.5 84.3 62.0 45.9 - − − Acanthaceae 3 Hygrophila schulli Leaf 19.0 54.7 61.0 16.8 - − − Acanthaceae 1 Andrographis paniculata Stem 17.0 60.8 49.6 6.71 - − − Acanthaceae 1 Andrographis paniculata Leaf 4.79 72.0 36.8 43.2 - − − Achariaceae 2 Hydnocarpus kurzii Leaf 64.0 0.18 78.6 29.2 * − Amaranthaceae 5 Alternanthera philoxeroides Leaf 68.9 29.2 82.7 41.0 ** Amaranthaceae 2 Cyathula prostrata Leaf 64.1 2.11 73.1 24.0 * Sustainability 2019, 11, 2649 6 of 18

Table 1. Cont.

Dry Samples Content Site (10 mL Agar 1) Score Family Botanical Name Plant Part − Code 10 mg 50 mg R% H% R% H% Anacardiaceae 1 Mangifera indica seed 37.3 9.11 86.0 52.0 - Anacardiaceae 2 Mangifera indica Leaf 19.5 8.72 54.7 30.4 - − Anacardiaceae 1 Mangifera indica Peel 18.4 19.7 69.6 42.4 - − Anacardiaceae 1 Buchanania lanzan Stem 6.8 29.9 2.56 53.9 - − − − Annonaceae 4 Artabotrys hexapetalus Leaf 29.5 4.53 55.1 14.7 - − Apiaceae 2 Centella asiatica Leaf 75.5 37.3 85.1 10.3 ** − Apiaceae 2 Cuminum cyminum seed 8.37 37.3 44.9 13.9 - − − Aplaceae 3 Foeniculum vulgare seed 28.7 0.53 62.9 31.0 - Apocynaceae 1 Holarrhena pubescens Leaf 74.7 44.8 92.3 79.0 ** Apocynaceae 1 Rauvolfia serpentine Leaf 72.7 16.2 81.0 28.0 ** Apocynaceae 1 Calotropis gigantean Leaf 65.9 1.49 82.3 16.6 ** − Apocynaceae 1 Tabernaemontana divaricate Leaf 44.3 18.8 75.3 18.6 - − Apocynaceae 1 Tabernaemontana dichotoma Flower 39.0 38.8 60.0 15.4 - − − Apocynaceae 1 Calotropis gigantean Stem 37.8 11.1 75.5 50.5 - − Apocynaceae 2 Nerium oleander Leaf 36.8 30.4 53.1 17.0 - − − Apocynaceae 1 Allamanda cathartica Leaf 33.0 38.9 62.8 37.8 - − − Apocynaceae 3 Holarrhena pubescens Leaf 22.4 53.7 23.3 53.4 - − − Apocynaceae 1 Hemidesmus indicus Leaf 13.2 67.5 48.6 17.3 - − − Apocynaceae 1 Nerium album Leaf 10.0 44.2 41.7 16.8 - − Apocynaceae 5 Alstonia macrophylla Leaf 6.05 89.7 32.4 33.1 - − − − Araceae 2 Dieffenbachia seguine Leaf 61.9 6.76 70.4 1.83 * − − Asparagaceae 1 Asparagus racemosus Root 13.2 46.2 70.6 18.5 - − Asteraceae 5 Eupatorium triplinerve Leaf 80.2 33.6 90.3 56.9 ** * Asteraceae 4 Ageratum conyzoides Leaf 77.2 17.4 88.5 67.7 ** * Asteraceae 4 Vernonia cinerea Leaf 71.0 11.6 76.3 6.26 ** Asteraceae 2 Brickellia baccharidea Leaf 62.3 10.3 76.3 7.77 * − Asteraceae 5 Spilanthes cliata Leaf 58.7 7.72 77.6 35.4 * − Asteraceae 2 Dittrichia viscosa Leaf 58.6 5.94 85.0 43.0 * − Asteraceae 2 Tagetes erecta Leaf 56.9 34.2 82.4 2.84 * − Asteraceae 2 Helianthus annuus Leaf 56.3 33.9 68.4 2.67 * − − Asteraceae 1 Tagetes erecta Flower 51.4 25.6 73.9 5.47 - − Asteraceae 4 Artemisia nilagirica Leaf 43.3 9.74 100 100 - − Asteraceae 1 Vernonia patula Leaf 43.0 4.58 69.2 17.4 - − − Asteraceae 4 Gigantochloa apus Leaf 37.5 13.6 66.4 11.3 - − Asteraceae 4 Wedelia chinensis Leaf 36.5 65.8 55.2 25.2 - − − Asteraceae 4 Mikania cordata Leaf 34.3 13.2 84.4 40.1 - − Asteraceae 4 Mikania micrantha Leaf 20.7 46.7 28.7 17.3 - − − Asteraceae 4 Blumea lacera Leaf 11.5 80.6 35.3 73.0 - − − Asteraceae 4 Bidens pilosa Leaf 4.74 82.6 29.9 84.0 - − − − Betulaceae 1 Betula alnoides Leaf 14.5 36.0 19.4 41.7 - − − Bignoniaceae 1 Parmentiera cereifera Leaf 58.6 12.8 85.7 42.9 * − Bignoniaceae 1 Stereospermum angustifolium Leaf 44.8 18.1 68.3 12.6 - − Bignoniaceae 1 Jacaranda mimosifolia Leaf 6.07 48.9 46.3 24.9 - − − Bombacaceae 1 Bombax ceiba Root 22.4 58.8 47.0 28.8 - − − Bombacaceae 3 Bombax ceiba Leaf 21.7 41.5 29.8 27.6 - − − Boraginaceae 5 Cordia dichotoma Leaf 65.1 25.6 87.4 26.9 ** − Boraginaceae 2 Coldenia procumbens Leaf 21.3 45.1 51.7 43.0 - − − Boraginaceae 4 Heliotropium indicum Leaf 19.0 66.0 42.7 12.5 - − − Bromeliaceae 4 Ananas comosus Leaf 13.2 7.36 38.9 1.40 - − Burseraceae 4 Canarium resiniferum Leaf 51.5 32.9 67.2 0.07 - − − Burseraceae 1 Protium serratum Leaf 24.6 51.5 58.9 15.3 - − − Caesalpiniaceae 1 Cassia renigera Leaf 52.5 3.40 84.9 25.4 - − Caesalpiniaceae 1 Pongamia pinnata Leaf 33.4 16.7 68.6 36.3 - − Caesalpiniaceae 1 Senna tora Leaf 30.5 57.0 61.2 1.59 - − − Caesalpiniaceae 1 Cassia angustifolia Leaf 20.1 16.7 64.0 13.4 - − Calophyllaceae 1 Calophyllum inophyllum Leaf 26.0 22.7 40.1 0.42 - − − Calophyllaceae 1 Mesua ferrea Leaf 1.01 55.5 26.2 27.2 - − − − Calophyllaceae 1 Mesua ferrea Flower 29.0 23.9 62.8 6.68 - − Caricaceae 2 Carica papaya Leaf 60.0 26.0 83.1 13.2 * − Combertaceae 1 Terminalia catappa Leaf 63.2 20.5 81.1 24.0 * Combretaceae 1 Terminalia chebula Leaf 64.7 6.28 89.7 63.1 * − Combretaceae 1 Terminalia belerica Leaf 16.9 36.1 64.1 4.34 - − − Combretaceae 1 Terminalia arjuna Leaf 16.4 24.8 83.1 12.8 - − Combretaceae 3 Terminalia chebula Fruit 0.82 62.3 49.4 3.26 - − − Commelinaceae 2 Commelina benghalensis Leaf 44.0 60.2 69.6 17.2 - − − Sustainability 2019, 11, 2649 7 of 18

Table 1. Cont.

Dry Samples Content Site (10 mL Agar 1) Score Family Botanical Name Plant Part − Code 10 mg 50 mg R% H% R% H% Commelinaceae 1 Commelina diffusa Leaf 37.0 62.5 66.3 2.32 - − Crassulaceae 4 Bryophyllum pinnatum Leaf 65.8 30.2 79.3 28.1 ** Cucurbitaceae 2 Cucumis sativa Peel 77.8 100 83.1 27.8 ** * − Cucurbitaceae 2 Cucurbita moschata Peel 61.6 21.3 74.3 43.1 * Cucurbitaceae 1 Gynostemma pentaphyllum Leaf 43.4 29.3 49.4 11.1 - − Cucurbitaceae 4 Coccinia grandis Leaf 40.2 7.44 89.1 37.9 - − Cucurbitaceae 2 Benincasa hispida Peel 10.1 42.2 57.4 2.71 - − Dilleniaceae 1 Dillenia indica Leaf 14.2 77.1 29.7 47.8 - − − Dipterocarpaceae 1 Dipterocarpus turbinatus Leaf 62.0 27.8 74.7 20.6 * − Dipterocarpaceae 1 Hopea odorata Leaf 40.1 10.3 68.6 5.85 - − − Dipterocarpaceae 1 Anisoptera scaphula Leaf 36.5 66.3 56.4 5.16 - − − Ebenaceae 1 Diospyros montana Leaf 68.5 15.4 76.2 56.5 ** Euphorbiaceae 4 Manihot esculenta Leaf 71.0 13.6 84.0 5.29 ** − − Euphorbiaceae 3 Euphorbia neriifolia Leaf 61.2 3.95 89.3 46.2 * − Euphorbiaceae 2 Euphorbia tithymaloides Seed 60.4 29.3 64.7 22.1 * − Euphorbiaceae 4 Euphorbia tirucalli Seed 53.6 17.5 76.4 41.7 * Euphorbiaceae 4 Cnesmone javanica Leaf 46.1 31.4 81.2 55.3 - − Euphorbiaceae 4 Macaranga tanarius Leaf 43.1 42.6 69.8 30.6 - − − Euphorbiaceae 2 Ricinus communis Seed 40.1 47.9 54.8 28.5 - − Euphorbiaceae 2 Ricinus communis Root 28.3 38.4 84.9 15.8 - − − Euphorbiaceae 3 Pedilanthus tithymaloides Leaf 25.6 58.5 67.2 25.2 - − − Euphorbiaceae 5 Croton roxburghii Leaf 29.3 13.1 42.1 13.9 - − − Fabaceae 2 Acacia concinna Fruit 95.4 64.2 96.3 72.8 ** ** Fabaceae 2 Saraca asoca Bark 81.5 18.4 87.4 40.7 ** * Fabaceae 4 Mucuna pruriens Leaf 76.8 33.0 88.9 52.5 ** * Fabaceae 4 Tephrosia candida Leaf 75.5 42.4 86.4 23.3 ** − Fabaceae 4 Senna alexandrina Leaf 74.8 17.3 83.9 60.9 ** Fabaceae 1 Senna alata Leaf 70.5 7.62 73.5 0.99 ** − Fabaceae 1 Senna siamea Leaf 58.7 19.1 72.6 10.5 * − − Fabaceae 5 Pisum sativum Peel 56.6 9.73 77.4 49.6 * − Fabaceae 2 Trigonella foenum-graecum Fruit 53.7 15.1 75.9 46.7 * Fabaceae 1 Indigo fera Leaf 50.5 41.1 51.0 5.71 - − Fabaceae 1 Cicer arietinum Leaf 48.5 94.5 71.5 13.3 - − − Fabaceae 1 Dalbergia Sissoo Leaf 46.3 20.0 75.3 36.1 - − Fabaceae 2 Millettia peguensis Leaf 40.2 30.3 68.4 24.5 - − Fabaceae 1 Cassia nodosa Leaf 38.7 24.5 78.4 21.9 - − Fabaceae 5 Glycyrrhiza glabra Stem 35.2 4.74 48.2 25.6 - Fabaceae 1 Vachellia nilotica Bark 12.4 56.3 10.2 67.9 - − − Fabaceae 2 Saraca asoca Leaf 11.6 73.0 12.5 0.47 - − Fabaceae 4 Cajanus cajan Leaf 3.75 84.8 7.94 113 - − − Flacourtiaceae 1 Flacourtia jangomas Leaf 28.0 3.40 62.1 35.8 - − − Fumariaceae 4 Fumaria indica Leaf 20.3 82.4 70.2 50.4 - − − Gentianaceae 6 Swertia chirayita Flower 24.8 2.35 53.1 16.2 - − Gentianaceae 6 Swertia chirayita Leaf 9.47 32.1 32.0 18.1 - − − Gentianaceae 6 Swertia chirayita Stem 4.00 25.1 33.7 5.47 - − Lamiaceae 2 Mentha spicata Leaf 47.3 0.25 69.8 36.0 - − Lamiaceae 3 Ocimum Sanctum Leaf 44.9 62.5 49.1 30.2 - − − Lamiaceae 1 Premna latifolia Leaf 42.1 13.5 67.1 8.64 - − − Lamiaceae 1 Tectona grandis Leaf 42.0 49.8 52.0 26.4 - − − Lamiaceae 4 Clerodendrum infortunatum Leaf 38.5 20.0 69.1 32.2 - − Lamiaceae 6 Hyptis suaveolens Fruit 32.7 21.6 68.4 10.6 - − Lamiaceae 4 Ocimum gratissimum Leaf 15.3 92.1 46.5 66.4 - − − Lamiaceae 4 Ocimum basilicum Leaf 12.6 72.0 49.0 55.5 - − − Lamiaceae 4 Vitex trifolia Leaf 2.60 57.1 47.5 22.2 - − − − Lamiaceae 6 Gmelina arborea Bark 73.9 1.47 89.0 26.7 ** Lauraceae 1 Cinnamomum verrum Bark 91.8 80.0 100 100 ** ** Lauraceae 3 Litsea glutinosa Leaf 41.4 11.8 61.7 39.3 - − Lauraceae 4 Cinnamomum camphora Leaf 36.6 24.5 84.9 85.9 - − Lauraceae 1 Cinnamomum verum Leaf 25.1 21.9 62.6 21.3 - − Lauraceae 2 Cinnamomum tamala Leaf 7.72 28.4 35.1 3.46 - − − Lecythidaceae 2 Couroupita guianensis Fruit 95.4 65.1 98.5 69.5 ** ** Lecythidaceae 2 Couroupita guianensis Leaf 71.9 11.8 80.3 46.0 ** Lecythidaceae 2 Couroupita guianensis Flower 44.4 26.5 63.7 13.2 - − Lecythidaceae 4 Careya arborea Leaf 67.8 5.42 66.6 24.0 ** − Sustainability 2019, 11, 2649 8 of 18

Table 1. Cont.

Dry Samples Content Site (10 mL Agar 1) Score Family Botanical Name Plant Part − Code 10 mg 50 mg R% H% R% H% Lecythidaceae 4 Barringtonia acutangula Leaf 46.2 67.2 76.1 21.1 - − − Lecythidaceae 5 Gustavia superba Leaf 20.7 29.2 40.6 38.5 - − − Liliaceae 1 Asparagus racemosus Root 37.9 29.9 54.3 4.53 - − − Linderniaceae 1 Lindernia procumbens Leaf 2.50 56.3 41.8 17.7 - − − Lythraceae 1 Lawsonia inermis Leaf 37.3 6.13 90.5 53.4 - − Lythraceae 2 Punica granatum Leaf 35.7 65.9 72.1 16.2 - − − Lythraceae 4 Lagerstroemia speciosa Leaf 10.6 72.6 65.9 0.59 - − − Malvaceae 4 Urena lobate Leaf 53.7 9.15 73.4 18.6 * Malvaceae 1 Sida acuta Leaf 51.2 30.9 75.1 9.84 - − Malvaceae 4 Urena lobate Stem 45.0 37.2 73.5 17.7 - − − Malvaceae 1 Sida cordifolia Leaf 44.9 16.5 72.1 20.0 - − − Malvaceae 2 Pterospermum semisagittatum Leaf 43.9 45.3 69.1 29.0 - − − Malvaceae 1 Heritiera fomes Leaf 15.1 28.6 60.5 5.27 - − − Malvaceae 1 Hibiscus cannabinus Leaf 8.25 150 44.6 121 - − − Malvaceae 1 Bombax insigne Leaf 23.1 80.0 6.99 71.9 - − − − Meliaceae 1 Azadirachta indica Leaf 83.3 77.3 89.0 81.3 ** * Meliaceae 6 Chukrasia tabularis Leaf 65.5 17.7 78.2 3.26 ** − − Meliaceae 2 Aphanamixis polystachya Leaf 37.6 58.4 100 100 - − Meliaceae 1 Swietenia macrophylla Seed 4.82 31.1 0.92 50.3 - − − Mimosaceae 1 Entada rheedei Fruit 58.4 17.6 78.5 46.3 * Mimosaceae 1 Mimosa pudica Leaf 45.8 1.12 63.2 20.6 - − Mimosaceae 2 Adenanthera pavonina Leaf 41.0 74.8 69.3 1.62 - − Mimosaceae 1 Xylia xylocarpa Leaf 35.4 52.4 60.5 20.5 - − − Mimosaceae 1 Calliandra ruba Leaf 17.3 22.8 52.8 0.88 - − − Moraceae 6 Artocarpus lacucha Leaf 47.9 27.9 66.9 5.39 - − − Moraceae 1 Artocarpus altilis Leaf 45.0 18.2 57.9 28.8 - − Moraceae 6 Ficus benghalensis Leaf 30.9 33.8 47.1 18.7 - − − Musaceae 4 Musa spp. Peel 6.02 90.8 41.0 33.3 - − − Myristicaceae 1 Myristica fragrance Leaf 28.0 7.85 58.9 44.4 - Myristicaceae 1 Myristica fragrance Fruit 11.5 18.9 51.7 57.0 - Flower Myrtaceae 1 Syzygium aromaticum 76.2 60.0 94.4 100 ** bud Myrtaceae 1 Syzygium firmum Leaf 55.9 12.1 79.3 33.6 * Myrtaceae 1 Psidium guajava Leaf 54.4 20.1 76.9 13.6 * − Myrtaceae 1 Psidium guajava Bark 11.6 22.1 51.0 9.76 - − − Myrtaceae 4 Melaleuca citrina Leaf 9.03 26.6 48.4 2.39 - − Myrtaceae 4 Syzygium cumini Seed 2.32 31.3 40.9 2.07 - − Myrtaceae 2 Syzygium fruticosum Leaf 0.62 37.9 50.2 13.3 - − − − Oleaceae 2 Jasminum scandes Leaf 37.3 7.50 69.7 26.2 - − Onagraceae 1 Ludwigia octovalvis Leaf 49.6 27.3 84.7 42.6 - Orchidaceae 6 Geodorum densiflorum Leaf 16.9 62.9 22.6 39.4 - − − − Oxalidaceae 2 Averrhoa bilimbi Leaf 28.1 15.8 57.6 5.49 - − Pandanaceae 2 Pandanus amaryllifolius Leaf 32.3 40.9 62.3 16.2 - − Pandanaceae 6 Pandanus tectorius Leaf 18.3 46.6 32.7 31.4 - − − Phyllanthaceae 6 Phyllanthus emblica Fruit 95.4 76.1 96.1 78.0 ** ** Phyllanthaceae 3 Phyllanthus urinaria Leaf 23.6 93.4 30.6 76.7 - − − Phyllanthaceae 6 Phyllanthus niruri Leaf 4.93 59.6 31.9 21.9 - − − Piperaceae 1 Piper longum Fruit 91.3 62.9 96.0 77.8 ** ** Piperaceae 1 Piper nigrum Fruit 77.5 59.2 87.0 74.2 ** * Piperaceae 1 Piper chaba Leaf 71.6 22.1 87.1 56.9 ** Plantagenaceae 1 Plantago scabra Seed 14.9 40.4 24.8 60.4 - − − Plumbaginaceae 2 Aegialitis rotundifolia Leaf 43.2 22.6 76.7 31.2 - − Poaceae 1 Axonopus compressus Leaf 75.6 20.3 83.9 43.6 ** Poaceae 1 Dendrocalamus longispathus Leaf 50.6 5.73 55.2 5.50 - − − Poaceae 1 Dendrocalamus giganteus Leaf 41.6 38.2 91.0 66.2 - − Poaceae 2 Cymbopogon citratus Leaf 34.8 27.6 100 100 - − Poaceae 1 Cynodon dactylon Leaf 31.0 54.8 38.0 37.3 - − − Poaceae 2 Dactyloctenium aegyptium Leaf 18.0 45.4 57.9 17.5 - − − Podocarpacea 1 Podocarpus neriifolius Leaf 74.7 53.6 99.2 100 ** Ranunculaceae 6 Nigella sativa Seed 68.2 39.2 70.7 41.4 ** Rhamnaceae 1 Ziziphus mauritiana Leaf 48.5 43.0 64.2 19.1 - − − Rhizophoraceae 1 Carallia brachiate Leaf 34.3 23.2 62.4 19.2 - − − Rubiaceae 5 Spermacoce mauritiana Leaf 54.7 8.17 66.6 5.86 * − Rubiaceae 4 Morinda citrifolia Leaf 52.4 7.77 82.5 52.8 - − Sustainability 2019, 11, 2649 9 of 18

Table 1. Cont.

Dry Samples Content Site (10 mL Agar 1) Score Family Botanical Name Plant Part − Code 10 mg 50 mg R% H% R% H% Rubiaceae 3 Paederia foetida Leaf 51.7 13.2 74.4 7.43 - − − Rubiaceae 1 Mitragyna parvifolia Leaf 47.4 5.50 73.0 18.4 - − Rubiaceae 1 Exeocaicaria bi-color Leaf 34.2 29.0 80.7 18.3 - − Rubiaceae 1 Haldina cordifolia Leaf 34.0 20.3 56.0 11.0 - − Rubiaceae 1 Gardenia coronaria Leaf 17.1 66.2 51.4 37.2 - − − Rutaceae 1 Aegle marmelos Leaf 86.1 14.3 74.8 0.79 ** * Rutaceae 6 Aegle marmelos Fruit 75.5 7.29 84.8 38.2 ** Rutaceae 4 Citrus medica Leaf 64.6 1.33 74.9 34.8 * − Rutaceae 2 Melicope triphylla Leaf 56.1 3.30 87.2 44.2 * − Rutaceae 1 Glycosmis pentaphylla Leaf 52.8 17.7 82.5 70.2 - Rutaceae 1 Murraya paniculata Leaf 49.0 2.09 77.9 37.8 - − Rutaceae 1 Limonia acidissima Leaf 47.4 15.1 65.1 11.2 - − Rutaceae 4 Clausena heptaphylla Leaf 39.3 10.3 75.1 35.2 - − Rutaceae 4 Citrus medica Bark 31.2 29.2 43.8 13.8 - − − Rutaceae 1 Zanthoxylum rhetsa Leaf 18.7 31.7 49.2 10.3 - − Sapindaceae 6 Sapindus mukorossi Fruit 82.8 39.0 91.1 52.5 ** * Sapindaceae 5 Lepisanthes rubiginosa Leaf 64.7 11.2 71.1 13.6 * − − Sapindaceae 1 Dimocarpus longan Leaf 63.3 10.2 76.4 6.74 * − Sapindaceae 1 Nephelium longana Flower 57.2 11.8 71.9 26.2 * − Sapindaceae 1 Litchi chinensis Leaf 55.2 16.1 75.2 48.5 * Sapindaceae 1 Lepisanthes alata Leaf 37.0 33.3 62.4 7.30 - − − Sapindaceae 1 schleichera oleosa Leaf 30.6 16.2 76.8 53.4 - − Sapindaceae 1 Dodonaea viscosa Leaf 3.49 65.1 79.5 27.6 - − Sapotaceae 2 Chrysophyllum cainita Leaf 83.5 5.51 76.8 0.46 ** * − Sapotaceae 1 Mahua longifolia Flower 60.3 37.4 65.5 30.3 * − − Sapotaceae 1 Mimusops elegi varigata Leaf 34.3 24.7 78.2 32.8 - − Sapotaceae 1 Mimusops elengi Leaf 29.6 30.2 44.6 23.5 - − − Scrophulariaceae 2 Limnophila repens Leaf 25.6 60.6 34.0 27.6 - − − Solanaceae 6 Datura metel Seed 33.7 18.3 49.0 4.63 - − Solanaceae 2 Solanum tuberosum Peel 23.9 14.3 56.2 23.7 - − Sterculiaceae 2 Abroma augustum Leaf 62.5 68.3 66.4 33.8 * − − Sterculiaceae 2 Sterculia villosa Leaf 37.2 15.4 55.2 32.1 - Theaceae 5 Camellia sinensis Leaf 39.3 41.2 63.1 40.1 - − Thymelaeaceae 1 Aquilaria khasiana Leaf 28.2 44.7 78.3 10.0 - − − Urticaceae 4 Boehmeria macrophylla Leaf 59.7 3.22 74.6 11.3 * − Verbenaceae 1 Duranta repens Leaf 84.2 39.3 80.8 27.1 ** * Verbenaceae 4 Lantana camara Leaf 57.4 19.7 85.2 61.8 * Verbenaceae 3 Clerodendrum indicum Leaf 42.9 51.6 77.8 23.0 - − − Verbenaceae 2 Lippia gerinate Leaf 30.8 40.3 62.0 34.5 - − Verbenaceae 1 Nyctanthes arbortristis Leaf 28.4 67.2 56.1 19.8 - − − Verbenaceae 2 Vitex negundo Leaf 24.1 44.1 50.4 7.20 - − − Zingiberaceae 6 Kaempferia galanga Root 71.3 29.4 82.1 68.9 ** Zingiberaceae 4 Curcuma roxburghii Leaf 38.5 16.1 72.6 40.7 - − Zingiberaceae 3 Curcuma aromatica Leaf 19.6 8.74 55.8 37.3 - − Site code indicates the areas of sample collection, 1. Dhaka National Botanic Garden, Dhaka—DNBG, 2. Sher-e-Bangla Agriculture University, Dhaka—SAU, 3. Bangladesh Agriculture University, Mymensingh—BAU, 4. Chittagong University, Chittagong—CU, 5. Jahangirnagar University, Savar, Dhaka—JU, 6. Local Market, Dhaka—LM. Score indicates the strong inhibitory activity of the test plant samples on the radicle inhibition of the (control plant) lettuce by the standard deviation variance (SDV), where: * = M + 0.5 SD, **=M + 1 SD, ** * = M + 1.5 SD, ** ** = M + 2 SD. Additional * means strong inhibition. M = Mean of radicle inhibition, SD = Standard deviation of length of tested lettuce radicle, R% = Radicle inhibition percentage, H% = Hypocotyl inhibition percentage.

3.2. Optimal Inhibition Effect by Allelopathic Plants The allelopathic evaluation of the plant samples was done by the different parts of the plants like leaf, stem, flower, bark, peel, fruits, root, and seed. The composition of plant parts among the samples were leaves 78%, followed by stems 3%, flower 3%, fruit peel 3%, roots 2%, seed 4% and fruits 5%. In the present study, it was revealed that among the plant parts, fruit part showed the most vigorous inhibitory activities on the test plant, compared to other tissues. In this experiment, the radicle inhibition area was modeled by the assembling evaluation of all plant samples under 10 mg Sustainability 2019, 11, 2649 10 of 18 dry plant material leaching treatment. Invariably, the modeling area was representing a selection of the (higher inhibitory activity) HIA, (moderate inhibitory activity) MIA, (lower inhibitory activity) LIA and non-inhibitory activity (NIA) plant samples that emulated the radicle inhibition area (high, medium, low), and the appendage elongation area (Figure3). Under the consideration of 10 mg of dry plant samples, the inhibition area was spread out from 0 to 95.4%. The fruit pulp of Couroupita guianensis showed the highest inhibitory effect 95.4%, followed by the fruit of Acacia concinna 95.4%, and fruit of Piper longum 91.3% of inhibition status on lettuce radicle. Although, some plant sample evaluations revealed that rather than inhibition, secondary metabolites leaching stimulated the radicle elongation of lettuce seedlings (0 to 23.1%). Bombax insigne caused 23.1% stimulation of lettuce radicle, − Sustainabilityfollowed by 2019 a leaf,, 11,, xx of FORFORGeodorum PEER REVIEW densiflorum (16.9%) and leaves of Alstonia macrophylla (6%). 10 of 18

100

75

50

25 Inhibition (%) Inhibition Inhibition (%) Inhibition 0

-25-25

Vitex trifolia

Vitex trifolia

Nerium album Nerium

Nerium album Nerium

Bombax Bombax insigne

Bombax Bombax insigne

Paederia foetida Paederia

Paederia foetida Paederia

Cynodon dactylon Cynodon

Cynodon dactylon Cynodon

Mikania micrantha Mikania

Mikania micrantha Mikania

Piper longum Piper

Syzygium firmum Syzygium

Piper longum Piper

Syzygium firmum Syzygium

Cordia dichotoma Cordia

Curcuma Curcuma roxburghii

Cordia dichotoma Cordia

Curcuma Curcuma roxburghii

Abroma augustum

Duranta repens Duranta

Abroma augustum

Nephelium longana Nephelium

Duranta repens Duranta

Nephelium longana Nephelium

Tephrosia Tephrosia candida

Tephrosia Tephrosia candida

Acacia concinna. Acacia

Acacia concinna. Acacia

Barringtonia acutangulaBarringtonia

Barringtonia acutangulaBarringtonia

Ageratum conyzoides Ageratum

Ageratum conyzoides Ageratum

Couroupitaguianensis

Couroupitaguianensis

Eupatorium triplinerve Eupatorium

Eupatorium triplinerve Eupatorium

Couroupitaguianensis Couroupitaguianensis

Figure 3.3. Area of radicleradicle inhibition.inhibition. Inhibition Inhibition considering considering 10 10 mg plant dry matter (representative((rrepresentative selections of of total totaltotal samples samples samples for for for modeling modeling inhibition inhibitioninhibition area). area) area) The.. T rangehe rangerange of area of of showed area area showed the lettuce thethe radiclelettuce lettuce radicleelongationradicle elongation and inhibition and inhibitioninhibition from 23.1 fromfrom to −23.1 95.4% to inhibition 95.4% inhibition state. state.. − The observationobservation ofof maximummaximum inhibitioninhibition status status can can be be used used to to evaluate evaluate the the higher higherigher potentiality potentialitypotentiality of ofallelopathic allelopathic plant plant species. species. The rate The of rate the inhibition of the inhibition is different is from different species from to species. species Inhibitions to species. by InhibitionstheInhibitions allelochemicals byby thethe allelochemicalsallelochemicals are exhibited by are relatively exhibited di ffbyerent relatively patterns different of changes, pattern suchs of as, chang the radiclees,, such color, as, thethe shaperadicleradicle of color,color, the root, thethe necrosis,shapeshape ofof darkenedthethe roroot, necrosis, and swollen darkened seeds, curlingand swollen of root seeds, axis andcurling reduction of root of axis the andsize reduction [37]. The fruit of the pulp size of [37][37]Couroupita.. TheThe fruitfruit guianensis pulppulp ofof ,Couroupita under the guianensis lower concentration,, underunder thethe (10 lowerlower mg) concentrationconcentration of treatment, (10caused(10 mg) mg) discoloration of of treatment, treatment, of caused caused lettuce discoloration discoloration sprouts root. of of Additionally, lettuce lettuce sprouts sprouts maturation root. root. Additionally and elongation,, maturation maturation areas turned and and elongationbrown with areas curling turned orientation brown with (Figure curling4). orientation (Figure 4).

Figure 4. Radicle discoloration in brown color and curling orientation orientation,,, by by Couroupita guianensis fruitfruit pulp, 10 mg treatment inin thethe lettucelettuce seedlings.

The fruit of Phyllanthus emblica exhibited dark brown or black and thin root pattern, and curling formation (Figure 5). This study foundfound thatthat lower lower (10 (10 mg mg dry dry samp sample)le) concentration concentration treatmenttreatment indicated indicated inincomplete radicle inhibition. However, increasing thethe concentration showed furtherfurther inhibition.inhibition. Couroupita guianensis ffruit pulp and Phyllanthus emblica fruitfruit showed inhibition of radicle of approximately 99% and around 97%,, respectively,, by 50 mg dry sample, whereas Cinnamomum verrum ((bark) showed complete suppression by 50 mg of the dry plant sample treatmenttreatment onon lettucelettuce seedlings. Sustainability 2019, 11, 2649 11 of 18

The fruit of Phyllanthus emblica exhibited dark brown or black and thin root pattern, and curling formation (Figure5). This study found that lower (10 mg dry sample) concentration treatment indicated incomplete radicle inhibition. However, increasing the concentration showed further inhibition. Couroupita guianensis fruit pulp and Phyllanthus emblica fruit showed inhibition of radicle of approximately 99% and around 97%, respectively, by 50 mg dry sample, whereas Cinnamomum verrum

(bark)Sustainability showed 2019, complete 11, x FOR PEER suppression REVIEW by 50 mg of the dry plant sample treatment on lettuce seedlings.11 of 18

Figure 5. 5. RadicleRadiclediscoloration discoloration in in dark dark brown brown or orblack black color color and and thin thin axis, axis, by Phyllanthus by Phyllanthus emblica emblicafruit, 10fruit, mg 10 treatment mg treatment in the in lettuce the lettuce seedlings. seedlings.

3.3. Selective Species:Species: Maximal Status of Inhibition The top eight inhibitory samples, namely, CouroupitaCouroupita guianensisguianensis (Fruit(Fruit pulp)pulp),, PhyllanthusPhyllanthus emblicaemblica (Fruit),(Fruit), CinnamomumCinnamomum verrum verrum(Bark), (Bark),Acacia Acacia concinna concinna(Fruit), (Fruit),Piper Piper longum longum(Fruit), (Fruit),Aegle marmelosAegle marmelos(Leaf), Duranta(Leaf), Duranta repens (Leaf),repens (Leaf), and Chrysophyllum and Chrysophyllum cainito cainito(Leaf) (Leaf) were were selected selected to check to check the the correlations correlations of inhibitionof inhibition and and the the weight weight of of dry dry plant plant matter. matter The. The sandwich sandwich experiment experiment furtherfurther proceededproceeded withwith an increasedincreased amount of plantplant samples.samples. The amount of plant sample was extended from 10 mg and increasedincreased toto 30,30, 50,50, 7070 andand 100100 mg.mg. EachEach experimentexperiment waswas replicatedreplicated fivefive times.times. TheThe percentagepercentage ofof inhibitioninhibition ofof lettucelettuce radicleradicle and and hypocotyl hypocotyl was was measured measured for for each each amount amount of of dry dry plant plant sample sample used used in thein the sandwich sandwich method. method. The correlation The correlation between between the inhibition the inhibition percentages percentages of radicle of and radicle hypocotyl and ofhypocotyl the eight of plants the eight species plants revealed specie thats reve thealed inhibition that the of inhibition radicles was of radicle more thans was the more inhibition than the of hypocotyls.inhibition of The hypocotyl correlations. The coe correlationfficient (0.605) coefficient suggested (0.605) that suggest the dryed plantthat the samples dry plant caused samples more inhibitioncaused more on radicleinhibition rather on than radicle the hypocotyls, rather than which the hypocotyls indicates that, which the radicleindicates is morethat susceptiblethe radicle to is plantmore leachates.susceptible to plant leachates. There was a positivepositive correlationcorrelation between the dry weight of thethe samplesample andand thethe percentagepercentage of inhibitioninhibition ofof radicleradicle andand hypocotyl.hypocotyl. With 10 mg of dry plant sample, Couroupita guianensis fruit pulp (95.9%)(95.9%) causedcaused the the highest highest lettuce lettuce radicle radicle inhibition inhibition followed followed by Phyllanthus by Phyllanthus emblica emblicafruit (95.9%), fruit (95.9Acacia%), concinnaAcacia concinnafruit (95.8%) fruit, (9Cinnamomum5.8%), Cinnamomum verrum bark verrum (92.7%), barkPiper (92.7%), longum Piperfruit longum (92.0%), fruitAegle (92.0 marmelos%), Aegleleaf (87.8%),marmelosDuranta leaf (87.8 repens%), leafDuranta (85.8%) repens and leafChrysophyllum (85.8%) and cainito Chrysophyllumleaf (84.8%) cainito (Figure lea6).f (84.8Duranta%) (Fig repensureleaf 6). showedDuranta 100%repens inhibition leaf showed with the 100% weight inhibition of 100 mg with plant the dry weight material of in100 sandwich mg plant method dry material which was in followedsandwich by methodCouroupita which guianensis was followedfruit pulp by (99.3%), CouroupitaPhyllanthus guianensis emblica fruitfruit pulp (97.7%), (99.3Piper%), longumPhyllanthusfruit (97.2%),emblica fruitAcacia (97.7 concinna%), Piperfruit longum (97.1%), fruitAegle (97.2 marmelos%), Acacialeaf concinna (91.4%), Chrysophyllumfruit (97.1%), Aegle cainito marmelosleaf (86.5%). leaf Interestingly,(91.4%), ChrysophyllumCinnamomum cainito verrum leafbark (86.5 showed%). Interestingly, 100% inhibition Cinnamomum at 50 mg verrum of dry material.bark showed 100% inhibitionThe lettuce at 50 mg hypocotyl of dry material. showed highest inhibition percentage (80.7%) with 10 mg Cinnamomum verrum bark, followed by Acacia concinna fruit (75.2%), Piper longum fruit (74.0%), Phyllanthus emblica fruit (67.8%), Couroupita guianensis fruit pulp (66.6%), Duranta repens leaf (55.9%), Aegle marmelos leaf (42.2%), and Chrysophyllum cainito leaf (34.0%) with theLatuca same sativa amount (Control) of plant sample in agar sandwich (Figure1007). Like radicle, the lettuce hypocotyl showedCouroupita 95.6% inhibitionguianensis (Fruit) whiley treated = 0.039x with + 96.1 100 r = mg0.921** dry y = 0.019x + 95.9 r = 0.982** Piper longum fruit and followed by Couroupita guianensisPhyllanthusfruit emblica pulp (Fruit) (87.5%), Phyllanthus emblica fruit y = 0.086x + 93.1 r = 0.860** (86.7%), Acacia concinna fruit (84.6%), Aegle marmelosCinnamomumleaf (70.0%), verrumDuranta (Bark) repens leaf (64.5%) and the y = 0.016x + 95.9 r = 0.935** lowest was Chrysophyllum cainito leaf (31.0%). InterestinglyAcacia concinna again, (Fruit)Cinnamomum verrum bark imposed y = 0.062x + 92.0 r = 0.925** 100% inhibition80 on lettuce hypocotyl at 50 mg weightPiper of longum the dry(Fruit) sample. Another noticeable subject was that the lettuce radicle inhibition percentage showedAegle marmelos a positive (Leaf) correlationy = 0.039x with + the86.8 increasingr = 0.853** 20 y = 0.180x + 82.4 r = 0.967** amount of Chrysophyllum cainito leaf. However, it showedDuranta repens a negative (Leaf) correlation with the inhibition RadicleInhibition % y = 0.020x + 84.4 r = 0.713* percentage0 of the hypocotyl. Chrysophyllum cainita (Leaf) 0 20 40 60 80 100 Dry weight (mg)

Figure 6. The positive correlation between the weight of dry plant samples and the percentage of radicle inhibition. Based on the Pearson correlation coefficient, (r) significantly correlated. Correlation coefficient higher than 5% (*), correlation coefficient higher than 1% (**).

The lettuce hypocotyl showed highest inhibition percentage (80.7%) with 10 mg Cinnamomum verrum bark, followed by Acacia concinna fruit (75.2%), Piper longum fruit (74.0%), Phyllanthus emblica fruit (67.8%), Couroupita guianensis fruit pulp (66.6%), Duranta repens leaf (55.9%), Aegle marmelos leaf Sustainability 2019 11 , , 2649 12 of 18

Latuca sativa (Control) Couroupita guianensis (Fruit) y = 0.039x + 96.1 r = 0.921** 100 y = 0.019x + 95.9 r = 0.982** Phyllanthus emblica (Fruit) y = 0.086x + 93.1 r = 0.860** Sustainability 2019, 11, x FOR PEER REVIEW Cinnamomum verrum (Bark) 12 of 18 Acacia concinna (Fruit) y = 0.016x + 95.9 r = 0.935** (42.2%), and Chrysophyllum cainito leaf (34.0%) with the same amount y of = 0.062x plant +sample 92.0 r = in0.925** agar 80 Piper longum (Fruit) sandwich (Figure 7). Like radicle, the lettuce hypocotylAegle marmelos showed (Leaf) 95.6% inhibitiony = 0.039x while + 86.8 treated r = 0.853** with 100 mg20 dry Piper longum fruit and followed by CouroupitaDuranta repens guia (Leaf)nensis fruit ypulp = 0.180x (87.5 +% 82.4), Phyllanthus r = 0.967** emblica % Radicle Inhibition 0 fruit (86.7%), Acacia concinna fruit (84.6%Chrysophyllum), Aegle marmelos cainita (Leaf)leaf (70.0y %= ),0.020x Duranta + 84.4 repens r = 0.713* leaf (64.5%) and0 the20 lowest40 was60 Chrysophyllum80 100 cainito leaf (31.0%). Interestingly again, Cinnamomum verrum bark imposedDry 100% weight inhibition (mg) on lettuce hypocotyl at 50 mg weight of the dry sample.

Another noticeable subject was that the lettuce radicle inhibition percentage showed a positive Figure 6. The positive correlation between the weight of dry plant samples and the percentage of correlationFigure 6. with The positivethe increa correlationsing amount between of Chrysophyllum the weight of drycainito plant leaf. samples However, and theit showe percentaged a negative of radicle inhibition. Based on the Pearson correlation coefficient, (r) significantly correlated. Correlation correlationradicle inhibition. with the Basedinhibition on the percentage Pearson correlation of the hypocotyl. coefficient, (r) significantly correlated. Correlation coefcoefifficientcient higher higher than than 5% 5% (*), (*), correlation correlation coef coeffificientcient higher higher than than 1% 1% (**). (**).

100 Latuca sativa (Control) y = 0.256x + 64.8 r = 0.953** Couroupita guianensis (Fruit) 80 Phyllanthus emblica (Fruit) y = 0.228x + 67.2 r = 0.909** Cinnamomum verrum (Bark) y = 0.251x + 79.3 r = 0.840** 60 Acacia concinna (Fruit) y = 0.110x + 74.9 r = 0.951** Piper longum (Fruit) y = 0.270x + 71.1 r = 0.956** 40 Aegle marmelos (Leaf) y = 0.374x + 30.6 r = 0.734* Duranta repens (Leaf) y = 0.122x + 50.6 r = 0.698

20 Chrysophyllum cainito (Leaf) y = -0.040x + 34.2 r = 0.424 HypocotileInhibition % 0 0 20 40 60 80 100 Dry weight (mg) FigureFigure 7.7. The positive positive correlation correlation between between the the weight weight of ofdry dry plant plant samples samples and and the thepercentage percentage of ofhypocotyl hypocotyl inhibition. inhibition. Based Based on onthe the Pearson Pearson correlation correlation coefficient, coefficient, (r) (r) si significantlygnificantly correlated. correlated. CorrelationCorrelation coecoefffificientcient higherhigher thanthan 5%5% (*),(*), correlationcorrelation coecoefffificient higher than 1% (**).

4.4. DiscussionDiscussion FromFrom 233233 plantplant species,species, 252252 BangladeshiBangladeshi plant samples were were collected collected and and studied studied A Amongmong th thee plantplant samples,samples, thethe fruitsfruits ofof CouroupitaCouroupita guianensis,guianensis, Phyllanthus emblica, emblica, andand AcaciaAcacia concinna concinna showedshowed thethe radicleradicle inhibitioninhibition valuevalue ofof 95.4%95.4% with 10 mg plant dry mat matter.ter. Here, Here, we we would would introduce introduce the the evaluatedevaluated highly highly bioactive bioactive potential potential of of allelopathic allelopathic plant plant species, species, which which have have not not been been reported reported yet yet as allelopathicas allelopathic species. species Two. Two new new plants plants with with high allelopathichigh allelopathic potential potential observed observed were the were fruit the pulp fruit of C.pulp guianensis of C. guianensisand fruits and of fruitsP. emblica, of P. whichemblica with, which minimum with minimum dry quantity dry quantity (10 mg) (10 aff mg)ected affected the radicle the andradicle hypocotyl and hypocotyl growth, respectively. growth, respectively. In this study In evaluated this study another evalua firmted inhibitoryanother firm specimen inhibitoryAcacia concinnaspecimenfruits Acacia (pods), concinna a tropical fruits southern(pods), a tropical Asia medicinal southern plant Asia already medicinal reported plant asalready a growth reported inhibitor as ona growth test plants inhibitor (dicotyledonous on test plants and (dicotyledonous monocotyledonous and monocotyledonous plants) [38]. Therefore, plants with) [38] the. Therefore approach, ofwith natural the approach or ecological of natural interaction or ecological of vegetation, interaction weed of management vegetation, can weed be management possible by direct can be or indirectpossible involvement by direct or ofindirect the allelochemicals involvement of through the allelochemicals suppression through of the radicle suppression development, of the radicle curling, discoloration,development, delayed,curling, slowing,discoloration, stunted delayed, root formation slowing, stunted [18,36,37 roo]. Althought formation leaves [18,36,37 and]. roots Although are the mostleaves common and roots sources are the of most allelochemicals, common sources it is also of allelochemicals noticeable in di, ffiterent is also parts noticeable of the plant, in different such as stems,parts of buds, the plant fruits,, such peels, as bark, stems, and bu seedsds, fruits, [39]. peels, However, bark, the and amount seeds [39] of allelochemicals. However, the variesamount from of oneallelochemicals tissue to another varies [40 from]. one tissue to another [40]. AAmember member ofof LecythidaceaeLecythidaceae family,family, Couroupita guianensis isis native native to to the the tropics tropics of of the the northern northern partpart of of South South America America and and the the West West Indies, Indies, especially especially Amazon rainforestrainforest.. It It has has always always been been a a botanicallybotanically fascinatingfascinating plant plant due due to to the the unique unique shape shape of the of flowersthe flowers and fruits,and fruits and, itand is widely it is widely spread asspread an ornamental as an ornamental plant in plant tropical in tropical and subtropical and subtr countriesopical countries in the world in the [41world]. It is[41] a. fast-growing It is a fast- Sustainabilitygrowing 2019deciduous, 11, x; doi: tree. FOR The PEER fruit REVIEW pulp of the plant is one of the highwww.mdpi.com/journal/ potential candidatesustainabilitys for this study. All parts of this plant (leaves, fruit, flowers, stems, roots, and seeds) have been reported to have medicinal value due to its properties, such as anti-inflammatory [42], allelopathic [43], wound healing [44], antimicrobial [44,45] and antioxidant [46,47]. Typically, the plant leaves appear to be the most consistent source of chemicals involved in phytotoxicity, while fewer and less potent toxins occur in roots [48]. The aqueous methanol extracts of C. guianensis leaves significantly Sustainability 2019, 11, 2649 13 of 18 deciduous tree. The fruit pulp of the plant is one of the high potential candidates for this study. All parts of this plant (leaves, fruit, flowers, stems, roots, and seeds) have been reported to have medicinal value due to its properties, such as anti-inflammatory [42], allelopathic [43], wound healing [44], antimicrobial [44,45] and antioxidant [46,47]. Typically, the plant leaves appear to be the most consistent source of chemicals involved in phytotoxicity, while fewer and less potent toxins occur in roots [48]. The aqueous methanol extracts of C. guianensis leaves significantly inhibited germination and growth of dicotyledonous plants and monocotyledonous weeds [43]. The fruit pulp of the plant has not been studied yet as a potential plant growth inhibitor in the context of weed management. It contains several chemical constituents, such as indigo, indirubin, tryptanthrin, isatin, triterpenes, phenolic compounds, couroupitine, stigmasterol, and other essential oils [49,50]. However, there is no detailed research information about these chemicals as plant growth inhibitors. Conversely, sterols and their derivatives promote and maintain growth and development in plants [51]. In our further study, we are pursuing to identify the effect of these candidates chemical as plant growth inhibitors and their applications as new allelochemical on plants. Further studies on these candidates may identify the specific bioactive allelochemicals from the fruit pulps of C. guianensis, that may be a potential alternative to the synthetic herbicidal compounds. Nonetheless, depending on different types of soils, morphologies, and physiologies, allelochemicals may show a different mode of action, compositions, and developments among the plants of the same genus, even species [52,53]. This report revealed for the first time that Couroupita guianensis fruit pulps have significant allelopathic potential in weed management by releasing bioactive secondary metabolites. Another promising allelopathic candidate in this study was the fruit of Phyllanthus emblica with 95.4% inhibition value. This plant is widely distributed in subtropical and tropical areas, and it contains ample amounts of superoxide dismutase and vitamin C [54]. This plant is famous as a traditional medicinal plant, widely used in Chinese herbal medicine and Indian Ayurvedic medicine [55]. The fruits, leaves, and bark of P. emblica are rich in polyphenol (primarily, gallic acid and ellagic acid) [56]. P. emblica fruit is used in Ayurveda and also clinical medicine. P. emblica fruit has been reported as an agent with antimicrobial [57,58], anti-inflammatory [59,60], and anticancerous properties [61,62]. It has been reported that it contains phenolic compounds that enthrall intense antioxidant activity and can protect the cells from the oxidative damage caused by free radicals [63]. However, P. emblica fruit contains a high amount of polyphenols (hydrolyzable tannins like Emblicanin A and Emblicanin B). Besides, excessive oxidation of phenol causes high toxicity and changing root color [64]. This study revealed that allelochemicals released from P. emblica reduced radicles growth and changed the color of the root of lettuce seedlings. However, the adverse effect of phytotoxins on the growth of a weed species at specific concentrations might cause less or no growth inhibition on other species [65]. Moreover, the interaction of bioactive allelochemicals disrupts physiological processes and hormonal balances of plants that obstruct the growth of other organisms [66,67]. However, another report identified, the relative germination ratio of root length of Indian chickpea inhibited when of aqueous leaf extract of Phyllanthus emblica increased with time and concentration [68]. Similarly, Japanese medicinal plant Emblica pectinate leaves exhibited 93% radical and 74% hypocotyl inhibition on lettuce plant [69]. However, P. emblica fruit was not revealed as potential allelopathic plant species. This study reported that Phyllanthus emblica fruit is another new significant allelopathic candidate in terms of sustainable weed management. The total area of inhibition study of the entire species revealed that Bombax insigne appeared with growth-promoting potentiality, promoting approximately 23% elongation under the screening by the sandwich method. The plant is locally known as Shalmali (Sanskrit), Shimul-Tula (Bengali), Didu (Andaman) attaining an extended height up to 36 m with widespread branches [70]. Bombax insigne is therapeutically relevant containing phytochemicals like alkaloids, flavonoids, phenols, triterpenoids, saponins, and cardiac sterols [71]. Considerably, all the species might that have an impact on the promotion of the plant growth exhibit the adverse effect. Growth promotion or successions studied by Booth and Mania [72] on North American grasslands and abandoned Japanese field, resulted in Sustainability 2019, 11, 2649 14 of 18 allelopathy as growth promotor can stimulate the growth of pioneer species on pasture [73]. This study is considering plant growth inhibitor rather than growth promotion to focus on sustainability factors in weed management. However, growth promoting allelopathic species and releasing secondary metabolites may create an opportunity for growth promoting allelopathic studies. According to sample screening and evaluations, potential eight species were further studied to examine the correlation of the relative concentrations (10–100 mg) of the plant material leaches and the increased suppression effect of the hypocotyl and radicle, respectively. However, it found that the inhibitory activity depended on the concentration of chemical extraction [74,75]. A higher level of active allelochemicals leachates may stop or reduce the growth of lettuce seedlings. More than 50 mg leached of dry fruit pulp of C. guianensis, suppressed nearly 100% of the length of the radicle of lettuce seedling. Consequently, the effect of allelochemicals resulted in higher inhibition of lettuce radicles than hypocotyls. Aslani et al. observed the inhibitory impact depending on the concentration of allelopathic plant extracts [76,77]. The high concentration of Coffea arabica fruit crude dry matter is an allelopathic 1 inhibitor for hypocotyls and rootlets of L. sativa [78]. Barbosa reported that 10,000 µgmL− concentrations of sesquiterpenes in Brazilian pepper were found to inhibit the radicle growth of cucumber and lettuce by 50.5–84.5% and 88.6–92.4%, respectively [79]. Consequently, this study exhibited that the effectiveness of allelochemicals imposed higher inhibition on lettuce radicles than hypocotyls. Another report by Fujii et al. also indicated that L-DOPA had either no or very little influence on the growth of hypocotyl of lettuce [80]. In contrast, some allelopathic metabolites in higher concentrations inhibit growth but stimulate growth at lower levels. Several scientists previously evidenced this phenomenon. Sujeeun and Thomas named it as a rescue effect [21,81–83]. Sujeeun and Thomas [21] speculated the consistency of physiochemical sorption of allelopathic compounds by the media used. Moreover, the precipitation or altered mobility of allelochemical related to pH changes can also be a reason behind this immobilization. The results of this research indicate the evolution of new allelopathy species to be used to its most significant advantage in natural herbicide discovery and development. Furthermore, it is necessary to identify the specific bioactive allelochemicals and to understand the composition and the mode of action of promoting allelochemicals.

5. Conclusions Evaluation of allelopathic species and discovery of natural herbicides can be a significant advantage for land use and sustainable weed management in the agroecosystem. Identification of those unknown allelopathic plants from Bangladesh might provide the opportunity for new natural herbicide development. This research was undertaken to evaluate the allelopathic potentialities of plants. Furthermore, understanding the mode of action and the prospect of an individual or combined allelopathic compounds is necessary. Consequently, to fulfill the demand for safe food for the vast populated and developing country, a salient natural alternative is necessary rather than the implementation of chemical pesticides, weedicides, and fungicides in the field. This study gives evidence that the fruit pulps of Couroupita guianensis and the fruit of Phyllanthus emblica are new potential allelopathic candidates due to releasing bioactive secondary metabolites that may promote sustainable weed management in agriculture.

Author Contributions: Conceptualization, K.B. and Y.F.; methodology, Y.F.; software, Microsoft Office 2016; validation, K.S.A., M.S. and Y.F.; formal analysis, K.B., N.H.; investigation, K.B., N.H. and M.A.; resources, N.H. and M.A.; data curation, K.B.; writing—initial draft preparation, K.B.; writing—review and editing, M.S., N.H., K.S.A.; supervision, Y.F. Funding: This research received funding from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. This work was also partly supported by JST CREST Grant Number JPMJCR17O2 and JSPS KAKENHI Grant Number 26304024. Sustainability 2019, 11, 2649 15 of 18

Acknowledgments: The authors thank the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) for providing the scholarship to the first author at Tokyo University of Agriculture and Technology. We also thankfully acknowledge to Shahanara Begum; Department of Crop Botany, Faculty of Agriculture; Bangladesh Agricultural University, Mymensingh, Bangladesh; Mowri Dhali Moni; Department of biochemistry and molecular biology, University of Chittagong; and the authority of Dhaka National Botanic Garden, Dhaka; for the support of the legal procedures of this experimental work. Conflicts of Interest: The authors declare no conflict of interest.

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