To make our modern agriculture successful, the use of new agricultural technology in a short span of 35-40 years have caused havoc by contaminating our soil, environment and food with toxic pesticides residues. Modern agriculture is exploitive of growth resources and has caused very serious problems such as environmental pollution through (i). contamination of underground drinking water resources, food and fodder with pesticides and nitrates, which are harmful to human beings and livestock, (ii). poor soil health/ soil Sickness leading to low soil productivity and (iii). poor quality of life. These problems may be overcome with the adoption of Organic Agricultural practices. The definition of Organic Agriculture used in this paper is "Organic Agriculture consists of those practices, which reduces the use of outside inputs viz., fertilizers and pesticides etc on the farm". Therefore, various types of allelopathic strategies may be used for (a) maintenance of soil fertility (use of crop rotations, Biological Nitrogen Fixation, crop mixtures, crop residues and leaf litter etc.), (b) weed management (cover crops, crop residues as mulches, intercropping, crop rotations, phytotoxic or allelopathic varieties and natural herbicides etc.), (c) insects pest management (cropping systems, resistant varieties, insecticidal allelochemicals etc.), (d) nematodes management (plant materials, oilseed cakes, nematicidal compounds etc.), (e) diseases management (cropping systems, crop residues, organic amendments etc.) and (f) use of allelochemicals as growth regulators. Therefore, research efforts are needed to utilise inhibitory allelopathic effects of plants for natural control of crop pests (weeds, insects, nematodes, pathogens), so that use of present pesticides' could be minimized or eliminated for developing Sustainable Organic Agriculture, keeping the environment clean for our future generations and reducing the cost of Organic food.
The phytotoxicity of high purity helvolic acid and a related compound, fusidic acid was assessed using multiple growth and biochemical endpoints performed on tissues of several plant species. Bioassay tests for phytotoxicity of helvolic (0.25 mM) and fusidic (0.50 mM) acids were conducted on weed and crop species including: germination/growth (seeds/seedlings) of hemp sesbania [Sesbania exalta (Raf.) Rydb.], sicklepod (Cassia obtusifolia L.), mung bean (Vigna radiata L.), wheat (Triticum aestivum L.), and cucumber (Cucumis sativa L.; leaf disk electrolyte leakage of corn (Zea mays L.) and giant ragweed (Ambrosia trifida L.) leaf tissues; and greening of etiolated tissues of hemp sesbania, sicklepod, wheat (Triticum aestivum L.), mung bean, and sorghum (Sorghum vulgare L.) tissues. Fusidic acid reduced the chlorophyll accumulation in hemp sesbania (95%), wheat (70%), mung bean (60%), sorghum (60%) and sicklepod (48%); helvolic acid at this low concentration had only weak effects, except in mung bean. Neither compound affected the germination at the concentrations used, but both inhibited the seedling growth of all test species except sicklepod and helvolic acid-treated hemp sesbania. Both chemicals increased the electrolyte leakage in corn and giant ragweed leaf disks after 48-h exposure. Overall these natural products have broad-range phytotoxicity and may affect the plants directly or indirectly via antibiotic effects on soil/rhizosphere organisms.
Medicinal plants contain an array of natural chemicals and often research has focussed on their pharmacological value. During 2004/2005, we investigated the potential of bioactive chemicals in medicinal plants to inhibit plant growth using a Lemna (Lemna aequinoctialis) bioassay. Aqueous extracts from plant parts (viz. leaf, stem, bark, root etc.) of 8 test species (Ageratum conyzoides, Acacia farnesiana, Acacia melanoxylon, Alphitonia excelsa, Castanospermum australe, Chamaesyce hyssopifolia, Melaleuca quinquenervia and Phyllanthus virgatus) were added to Lemna nutrient medium resulting in a 2% extract concentration. Then using digital photographs, the growth of the Lemna was measured for 7 days using Scion computer software. Extracts from all eight species affected the growth of L. aequinoctialis, with the strongest growth inhibition coming from stem and bark extract of A. melanoxylon (98% and 91% growth inhibition, respectively), leaf extract of P. virgatus (91 % growth inhibition) and leaf extract of A. conyzoides (88 % growth inhibition).
Based on earlier research, phenol 2,4-bis(1,1-dimethylethyl) provides the resistance against the verticillium wilt in eggplant cultivars. We studied the effects of phenol, 2,4-bis(1,1-dimethylethyl) on germination and growth of eggplant, mycelium growth of Verticillium dahliae and incidence of verticillium wilt in bioactivity tests and field experiments. The low concentrations (0.05 mmol· L -1) significantly increased the germination rate, germination index, vigour index and radicle length of eggplant, but the high concentrations (0.10-1.00 mmol· L -1) inhibited all the germination indexes. In field experiment, the low concentration (0.05 mmol· L -1) slightly promoted the stem diameter and dry weight, improved the root activity and polyphenol oxidase (PPO) activity but decreased the content of malondialdehyde (MDA), chlorohpyll and activities of phenylalanine ammonia-lyase (PAL) and peroxidase (POD). The growth of eggplants was stunted at high concentrations (0.10-1.00 mmol·L -1). The mycelium growth of Verticillium dahliae was drastically decreased with the increasing concentrations (0.50 to 2.00 mmol· L -1). The 0.05 mmol·L -1 concentration proved most suitable to enhance the resistance against verticillium wilt and its control in eggplant.
Plant essential oils possess the biological activities, such as antibacterial, antifungal and antioxidant properties (12,14,15,26,50). The plant essential oils also exerted allelopathic effects on other plants (4,5,19,32,40). The Tagetes minuta and Schinus areira oils inhibits the root growth of Zea mays seedlings (38). Costunolide and parthenolide, isolated from the leaves of Magnolia grandiflora L, exhibited allelopathic potential on wheat (Triticum aestivum L.), lettuce (Lactuca sativa L.), radish (Raphanus sativus L.) and onion (Allium cepa L.) (2). Currently, the plant essential oils are being tried as potential candidates for weed (9), pest and disease management (1,20). The Eucalyptus urophylla is dominant specie in man-made forest communities in South China (23). However, in the past few years, there has been a growing concern on the excessive plantations of Eucalyptus which has decreased the biodiversity. Allelopathy is considered to be a major cause of understory suppression by Eucalyptus (25,27,29,46).
Whitetop (Cardaria draba) is a noxious perennial weed found throughout the world and exhibits a wide range of ecological tolerance It is very competitive with several crops ranging from field crops to fruit trees, has little economic value and is toxic to cattle. The weed quickly forms pure colonies that are impossible to be invaded by other plant species and surrounded by an inhibitory zone. Although it prefers alkaline conditions, it is highly successful in different soil types. Its ability to reproduce from seeds and vegetatively by creeping roots, make it difficult to control by traditional weed control methods. The large proportion of belowground tissue and the wide variation in phenology among plants at a given time, causes difficulty in chemical control. This species interferes with other plant species through competition and allelopathy. Shoot and root extracts, plant residues, volatiles and foliage leachates all exhibited phytotoxicity.
PCR-RFLP analysis, a culture-independent method was used to compare the bacterial community structure in two contrasting types of soils: soil monocropped with rice and soil rotated with different kinds of vegetables. Bacterial 16S rRNA gene (16S rDNA) libraries of the two types of soils were built and the 16S rDNA were then reamplified and digested with restriction endonuclease (Hinf I). In the vegetable soil, there were total 33 16S rDNA genotypes in 75 recombinants, while in rice soil there were total 17 16S rDNA genotypes in 55 recombinants. Compared to the rice paddy soil, the vegetable soil showed higher bacterial diversity index and most of the clones belonged to Proteobacteria γ, α and β subdivisions, while a few clones were affiliated with high G+C bacteria, Chloroflexus and Nitrospina bacteria. In rice soil, half of the clones belonged to Proteobacteria γ and β subdivisions, with the remaining half belonging to high G+C bacteria, Prosthecobacter and Sphingobacterium.
Sugarcane is crop of tropical and subtropical regions mainly cultivated for sugar production. It has been cultivated for thousands of years, hence, its morphology, biology and ecology are well known. It is source of sucrose and several of its bioactive compounds and possess pharmaceutical and plant defence properties. Intra and interspecific allelopathy have been described for sugarcane. In this review, sugarcane is presented as source of several allelopathic compounds, as evident from laboratory, pot and field studies.
Augustin Pyramus de Candolle (1778-1841) was one of the pre-eminent botanists of the nineteenth century. He is best remembered for his contributions to plant systematics; however, he is the first scientist to provide a comprehensive account of allelopathy. His considerations of root excretions commenced in 1805, and culminated in his theory of crop rotation, based on the idea that plants leave behind excremental matter that is particular harmful to the same species. De Candolle's ideas dominated from 1830-1840, but scientists at that time lacked the technology to discover the compounds required to vindicate his theories.
Changes in the morphometry (dorsal and ventral plates and posterior spine lengths of lorica) of Lecane stokesii were quantified with or without the presence of allelochemical asplanchnin from the predatory rotifer Asplanchnopus multiceps. As in many other species of Lecane, the dorsal plate of L stokesii is wide, the ventral plate is long (total lorica length, excluding spines 130-138 μm) and there is a linear relation between the length and the width of lorica. Compared to the size of L stokesii lorica cultured without asplanchnin, animals cultured in a medium with this allelochemical showed significant increase (up to 10%) in the size of lorica. The posterior spines of L stokesii grew 25% longer, when cultured with asplanchnin than those cultured without asplanchnin. However, we did not observe significant changes in the anterior spine lengths of L stokesii, when cultured with or without asplanchnin in the medium. The presence of two posterior spines of lorica appeared as a stable taxonomie character of L stokesii that distinguished it from L ohioensis or L ludwigii.
Passion fruit (Passiflora incarnata and Passiflora edulis) is medicinal plant and widely grown in tropical and subtropical countries for edible fruits and medicines. In bioassay and greenhouse studies, application of plant materials significantly inhibited the germination and growth of indicator plants and major paddy weeds. In field trial, plant materials applied at 1-2 ton ha -1 reduced the initial growth of paddy weeds by 70% and increased rice yield by 30%. The allelopathic properties of plant parts followed as the order: Leaf > stem> root. Numerous chemical substances belonging to alkaloids, phenolics, flavonoids, and volatiles were found in these plants, of which kavain, yagonin, dihydromethysticin and coumarin completely suppressed the barnyardgrass growth at 500 mg L -1. Hence Passion fruit may be used as natural herbicide to reduce the dependency on synthetic herbicides and other agrochemicals.
Barley is integrated with other crops to inhibit weed growth, through allelopathic interactions. Effects of barley on growth of other crops, weeds and autotoxicity among cultivars result primarily from allelopathy mediated by allelochemicals released from plant components and/or exuded from living roots. A limited number of allelochemicals are identified that contributes to allelopathic effectiveness of barley. High allelopathic effectiveness of barley has resulted in its wide adoption as a cover crop in sustainable agricultural systems for weed management. The allelopathic effectiveness varies among the barley cultivars, hence, selection programmes might improve the allelopathic potential of new cultivars used for weed management. Allelochemicals in barley may be candidates for natural herbicides and innovative approaches for integrating barley cover cropping with other cultural practices to improve the sustainable or ecologically-based weed management.
environment. It is one of the hotspots in Ecology and Agronomy. In this paper, we have retrieved from the Web of Science (WoS) SCI-E database the allelopathy-related studies (1960-2019). The Annual Number of Publications, Authors, Countries, Institutions, Journals and Keywords were analyzed by the bibliometric method to determine the research trends and hotspot changes in this field over the past 6 decades. From 1960-2019, the WoS database included 4,114 studies in the field of plant allelopathy. During this period of 60 years, the number of publications has gone through three stages: (i). Initial Stage (1960-1990), (ii). Growing Stage (1991-2009) and (iii). Stable Stage (2010-2019). The studies were conducted by 9,956 authors at 2,166 institutions across 100 countries. The United States, China, and Japan have the highest number of publications. The top three institutions with the highest number of publications are the Chinese Academy of Sciences, Kagawa University and USDA, USA. The top three authors are H. Kato-Noguchi, F.A. Macias, and C.H. Kong. The major Journals in this field are: (i). Allelopathy Journal, (ii). Journal of Chemical Ecology and (iii). Plant and Soil. The results of keyword clustering showed that the main research directions in this field are: (i). Metabonomics undergoing allelopathy, (ii). Functions of allelopathy substances, (iii). Molecular biology, (iv). Allelopathy of aquatic plants, (v). Alien plants invasion and (vi). Application of plant allelopathy in agroforestry production. Plant allelopathy is a research field that aims to maintain stable development. Future studies should focus on strengthening the cooperation among international scholars in plant allelopathy research and improving the output in frontier and hotspot areas.
HPLC quantitative analysis of 2,4-dihyroxy-7-methoxy-1, 4-benzoxazin-3- one (DIMBOA) in seedling of 3 wheat varieties (Zhongfu 9507, Jing 411 and Zhongbeizhong 39) shoots showed that DIMBOA concentration could be induced by several chemicals [Methyl jasmonate (JA), methyl salicylate (SA), triadimefon, potassium dihydrogen phosphate (KH 2PO 4) and cupric chloride (CuCl 2)] in different concentrations. The inducement effects on DIMBOA content in hydroponic solution were not obvious, but the inducement effects on DIMBOA production of shoot in wheat seedlings followed the order: JA > SA > triadimefon > KH 2PO 4 > CuCl 2. Common inducers such as JA and SA showed significant inducement effects, whereas, the effects of systemic fungicide triadimefon and the fertilizer KH 2PO 4 were weak. A heavy metal ion CuCl 2, showed inhibitory effects on Zhongfu 9507. The optimal concentration of JA is 561.0 μg/ml (2.5 μmol/ml), which was much higher than any other treatments.
This study was designed to evaluate the antifungal activities of pure oxygenated monoterpenes (borneol, borneol acetate, camphor, carvone, 1,8-cineole, citronellal, β-citronellol, dihydrocarvone, fenchol, fenchone, geraniol acetate, isomenthol, limonene oxide, linalool, linalool acetate, menthol, menthone, nerol, nerol acetate, terpinen-4-ol and α-terpineol) against 31 plant pathogen fungi in in vitro mycelial growth assays. Among the tested compounds, β-citronellol, nerol, menthol, terpinen-4-ol, α-terpineol, carvone, borneol and commercial benomyl had potent inhibitory effects against most of the tested fungal species. In particular, β-citronellol and nerol completely inhibited the growth of assayed fungi. Their inhibitory effects were also more stronger than commercial benomyl. Based on these results, β-citronellol, nerol as well as menthol, α-terpineol and terpinen-4-ol may be used as new antifungal compounds against plant pathogenic fungal species in agriculture.
Mikania micrantha H.B.K. is one of the world's worst weeds. It has caused serious damage to natural ecosystems and plantation crops. The successful invasion of M. micrantha is due not only to its wide eco-physiological tolerance and strong reproduction but also to its allelopathic effects on neighboring plants This paper mainly reviews the research on M. micrantha allelopathy. This weed produces a variety of allelochemicals (phenolics, flavonoids, alkaloids, terpenes) that can be released by volatilization, lixiviation of aerial parts and decomposition of plant debris in the soil. M. micrantha had allelopathic effects on crops, weeds, co-occurring plant species, insects and pathogens. Its allelopathic potential is modified by environment factors and changes in plant tissues. Its allelopathic potential clearly facilitates its successful invasion.
Bermudagrass [Cynodon dactylon (L.) Pers] is a C4 perennial grass and is one of the 10 worst world weeds. Its roots produces phenolic acids and cyanogenic compounds, which adversely impacts the growth and yield of field crops. Its rhizomes contains laevulose, triticin, vanillin, saponin, agropyrene (antimicrobial substance), iron and other minerals. Bermudagrass is used in traditional medicine as an anti-inflammatory, diuretic, antiemetic and purifying agent and to treat dysentery. Its essential oil has weak activity against some microbes.
Soil acidification due to excess use of nitrogen fertilisers in Chinese greenhouses is threatening the vegetable production through aluminum (Al) toxicity and low pH stress. We examined the changes in N assimilation in cucumber seedlings (Cucumis sativus L. cv. LuMing No. 1) under Al toxicity and H+ stress in presence/absence of 24-epibrassinolide (EBL), a potent allelochemical. Al toxicity suppressed the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamate synthase (GOGAT) but not glutamate dehydrogenase (GDH), causing the accumulation of nitrate (NO3−) and ammonium (NH4+) in plants and reducing the shoot dry weight, root dry weight and plants height. H+ stress did not affect the plant growth but slightly altered the N assimilation pathway with significant increase in NR and GS/GOGAT activity and drastic decline in GDH activity. The spray of EBL on plant shoots, overcame the growth inhibition of Al toxicity through elevating the antioxidant capacity and enhancing the N assimilation enzymes, but had no effect on N assimilation in plants subjected to H+ stress. In acidic soils, Al3+ stress instead of H+ stress significantly suppressed the nitrogen assimilation by vegetable crops and exogenous EBL alleviated the adverse effects of Al toxicity on nitrogen assimilation.
Allium is medicinal genus, rich in carbohydrates and organic-sulphur compounds such as Allicin (a precursor for the production of alkaloids, saponins and glycosides). Many phytochemicals have been isolated from various species of this genus, but only few (Allinase and Ajoene) are active as pesticides. Leaf extracts of garlic (A. sativum) controls 98% growth of citrus nematode (Tylenchulus semipenetrans). Allium cepa, A. sativum, A. fistulosum and A. ampeloparasum are fungicidal against the Alternaria alternata, A. brassicola and Myrothecium roridum. The phenol and sulphur based allelopathic compounds of genus Allium can be used for weeds and insects management in agricultural systems.
We grew cucumber in pots in greenhouse for 9-successive cropping cycles and analyzed the rhizosphere Pseudomonas spp. community structure and abundance by PCR-denaturing gradient gel electrophoresis and quantitative PCR. Results showed that continuous monocropping changed the cucumber rhizosphere Pseudomonas spp. community. The number of DGGE bands, Shannon-Wiener index and Evenness index decreased during the 3rd cropping and thereafter, increased up to the 7th cropping, however, however, afterwards they decreased again. The abundance of Pseudomonas spp. increased up to the 5th successive cropping and then decreased gradually. These findings indicated that the structure and abundance of Pseudomonas spp. community changed with long-term cucumber monocropping, which might be linked to soil sickness caused by its continuous monocropping.
Eupatorium adenophorum is worldwide-spread invasive plant. This review focussed on unique metabolite, Euptox A, released by this plant and its importance in invasion, use and control. Based on previous literature, it is concluded that the mechanism of the invader’s success has a close relationship with a special compound, Euptox A. Its release and degradation mostly determines the spread of E. adenophorum. Besides, the control and use of this invasive species should consider the toxicity of Euptox A. This review suggests that the secondary metabolite, Euptox A, might be a key in controlling and using this invasive plant. This review will increase our knowledge of the role of a natural chemical in biological invasion.
Three water-soluble compounds were isolated and characterized from the rhizomes of Polygonatum cirrhifolium. Their structures were determined as (25A)spirost-5-ene-3β-ol-3-O-α-L-rhamnopyranosyl( 1 → 2)-[α-L-rhamnopyranosyl ( 1 → 4)]β-D- glucopyranoside (A), (25R)-spirost-5-ene-3β-ol-3-O-[a-L-rhamnopyranosyl (1→4)]-β-D- glucopyranoside (B) and n-butyl- β-D-fructopyranoside (C). These compounds were isolated first time from P. cirrhifolium and their antifungal activity was tested against growth of 11 plant pathogenic fungi. The compound A (3-sugars linked at C-3) drastically inhibited the growth of Exserohilum turcicum and Botryosphaeria ribis than compound B (2-sugars linked at C-3), with EC 50 of 46.8 and 57.5 μg/ml, respectively. Diosgenin (the aglycone of compound A and B) was also more inhibitory to growth of Fusarium oxysporum with EC50 of 288.4 μg/ml.
Isolation and identification of allelochemicals is an important step to study allelopathy. Our previous work demonstrated that Streptomyces strain 6803 showed allelopathic effects on both plants and plant fungal pathogens. In this study four macroporous resins (S-8, X-5, AB-8 and HP-20) were used to collect the allelochimcals from the fermentation broth of Streptomyces strain 6803. Among the four resins HP-20 macroporous resin had the highest adsorption capacity for bioactive compounds from the fermentation broth. Three allelochemicals [5,7-dihydroxyflavone (I), 5-hydroxy-7-methoxy- flavone (II) and di (2-ethylhexyl) phthalate] were isolated and purified from the fermentation broth of this strain by column chromatography. Their structure was identified by ESI-MS, 1HNMR, 13CNMR and IR. All isolated compounds showed herbicidal activity. Compound I and II inhibited the root growth of rape (Brassica campestris L.) by 71% and 69% at a concentration of 0.3 mmol/L, respectively. The mean diameter of inhibition zone of compounds I, II and III at 0.3 mmol/L were 22.4, 25.5 and 26.1 mm against the fungal pathogen Fusarium graminearum and 18.9, 16.2 and 15.8 mm against Glomerella cingulata (Stonem), respectively. Our results suggest that HP-20 resin can be efficiently used to collect the allelochemicals from microbial fermentation broth and the compounds I, II and III were responsible for phytotoxic and antifungal activities of Streptomyces strain 6803.
Streptomyces spp produces numerous antibiotics to inhibit the growth of neighbouring microbial competitors, however, their potential allelopathic effects on plants is ignored. Streptomyces sp. strain 6803 was isolated from the rice soil. This strain showed allelopathic effects on both fungal. pathogens and plants. Ten allelochemicals were isolated and purified from fermented broth of the strain through column chromatography. Their structure was identified on the basis on their IR, MS, 1H and 13C NMR. The identified compounds are: 7, 4'-dihydroxy- flavone (I), 5,7dihydroxy -8-methoxyflavone (II), 5,7,4'-trihydroxyfiavone (Apigenin, III), 5,7,4'trihydroxy- isoflavone (Genistein, IV), diisobutyl phthalate (DiBP, V), dibutyl phthalate (DBP, VI), 4-hydroxy -benzoic acid (VII), salicylic acid (VIII), benzoic acid (IX), N-acetyl- tyramine (X). Bioassay showed that all isolated compounds had phytotoxicity. Among them the phenolic compounds (VII-IX) displayed higher phytotoxicity. Compound VIII inhibited the root growth of barnyardgrass (Echinocliloa crusgalli) and rape (Brassica campestris L.) by 86.6 and 100%, respectively at 0.3 mM concentration. The flavones (I-IV) showed strong antimicrobial activity. The compounds II, III and IV at 0.3 mM inhibited the Fusarium graminearum in 25.0, 26.6 and 28.2 mm diameters, respectively. However, these flavones were less allelopathic to plants than phenolic compounds. Our results suggested that Streptomyces sp. strain 6803 uses flavone compounds for resistance to microbes and phenolic compounds for allelopathic effects on plants.
To understand the process of natural regeneration failure in Abies pindrow forests in western Himalayas, the allelopathic interactions of one under-storey shrub species (Viburnum nervosum D. Don) were studied with keystone species (Abies pindrow Spach). The effects of foliage leachates (0%, 5%, 10%, 15%. 20%) of V. nervosum were investigated on the seed germination, radicle, plumule and seedling growth of A. pindrow. The leachate concentrations inhibited the seed germination, radicle and plumule growth, seedling height and seedling basal diameter of the receptor species. Trans-5-p-coumaroylguinic acid, p-coumaric acid, m-coumaric acid and flavanol were identified as phenolic phytotoxins produced in V. nervosum leaves, which may be responsible for the inhibition of various physiological processes in receptor tree species. Allelopathic interactions of V. nervosum may explain the relative absence of seed germination, poor establishment and growth of seedlings of A. pindrow on the forest floor in these temperate forests. Knowing such tree/under-storey interactions can help the foresters in regenerating these forests by manipulating the silvicultural practices. However, further research is required to identify such other allelopathic interactions in natural habitat of forest tree species in the region.
To understand the process of natural regeneration failure in Abies pindrow forests in western Himalayas, allelopathic interactions of one understorey shrub species (Sarcococca saligna (D. Don) Muell.-Arg.) with the keystone species (Abies pindrow Spach) were studied. The effects of foliage leachates (0, 5%, 10%, 15% and 20%) of Sarcococca saligna were investigated on the seed germination, radicle, plumule and seedling growth of Abies pindrow. The leachate concentrations significantly inhibited the seed germination, radicle and plumule growth, seedling height and collar diameter of receptor species. The rate of inhibition increased with the increase in concentrations of leachates. Four phenolic compounds viz., neochlorogenic acid, trans-5-p-coumaroylguinic acid, kaempferol-3-Oglucopyranoside and flavanol were identified from the foliage leachates of Sarcococca saligna, which may be responsible for inhibiting the various processes in tree species. It seems that the dynamics of Abies pindrow - understorey (Sarcococca saligna) interactions created unfavorable conditions for the regeneration of Abies pindrow on the forest floor.
We grew cucumber in pots in greenhouse for 9-successive cropping cycles and analyzed the rhizosphere Pseudomonas spp. community structure and abundance by PCR-denaturing gradient gel electrophoresis and quantitative PCR. Results showed that continuous monocropping changed the cucumber rhizosphere Pseudomonas spp. community. The number of DGGE bands, Shannon-Wiener index and Evenness index decreased during the 3rd cropping and thereafter, increased up to the 7th cropping, however, however, afterwards they decreased again. The abundance of Pseudomonas spp. increased up to the 5th successive cropping and then decreased gradually. These findings indicated that the structure and abundance of Pseudomonas spp. community changed with long-term cucumber monocropping, which might be linked to soil sickness caused by its continuous monocropping.
The genus Abutilon has more than 80 spp., distributed in tropical and subtropical countries. Some spp. (e.g. A. asiaticum, A. indicum, A. persicum, A. theophrasti) are cultivated as crops for fibre and medicines in China and Tibet. The information about distribution of its 24 spp. is available. Abutlion theophrasti is major weed spp. which reduces the crops yields. It is propagated through seed. Bioassays, pot culture and field studies revealed that all plant parts viz., seed, shoot, root are toxic to crop plants and some fungal spp. Its glandular trichomes on stem and petioles exude very phytotoxic exudates, The quantity and phytotoxicity of exudate vary with site and climatic conditions. The allelochemicals have been identified as amino acids, phenolic compounds, flavonoids and terpenoids, phytotoxic to germination and seedling growth of crops and have fungitoxic effects. The fungitoxic properties needs to be exploited for management of pathogens.
