What makes Allium species effective against pathogenic microbes?

The antimicrobial activity of garlic (Allium sativum L.) has been known since ancient times. The first citation dates back to the Egyptian period of fifteenth century BC when garlic was reported to be used in folk medicine as a remedy for microbial infections. Scientific investigations on garlic started in 1858 with the work of Pasteur who first noted antibacterial properties of garlic extracts. From that date to the discovery of antibiotics, garlic has been used against amoebic dysentery and epidemic diseases such as typhus, cholera, diphtheria, and tuberculosis. But what makes garlic and Allium species effective against pathogenic microbes? The volatile allicin and other thiosulfinates, giving pungency to Allium plants, are well-studied antimicrobial agents. The thiosulfinates can decompose to form additional sulfur constituents, including diallyl, methyl allyl, and dipropyl mono-, di-, tri- e tetra-sulfides, and (E)- and (Z)-ajoene without losing antimicrobial activity. Besides these compounds, onion and garlic are characterized by polar compounds of steroidal and phenolic origin, often glycosilated, not pungent and more stable during cooking, showing also antimicrobial activity. Recently, there has been increasing scientific attention given to such compounds. Nitrogen organic compounds, like alkaloids and polypeptides, have also been isolated from these plants and have shown antimicrobial activity. In this paper, the literature about the major volatile and non-volatile organic compounds of garlic and other Allium plants has been reviewed. Particular attention is given to the compounds possessing antimicrobial activity and to the correlation between the observed activity and the chemical structure of the tested compounds.     

A comparative study of sulphur content of someAllium L. Species

Garlic has been used worldwide as a folk medicine to cure a wide range of diseases. AlthoughAllium sativum is the species commonly used, several otherAllium species have been used as a substitute for common garlic, especially in the past. This work compares the extracts from bulbs of common garlic with those of otherAllium species. TLC analysis was used to compare the sulphur compounds inA. sativum, A. subhirsutum, A. pendulinum, A. roseum, andA. triquetrum. Results have showed that the use of the above mentioned wildAllium species is not without scientific support.     

Bioactive polar natural compounds from garlic and onions

Bioactive natural compounds from garlic and onions have been the focus of researches for decades, firstly due to their pharmacological effects, and secondly due to their defence properties against plant diseases. In fact, garlic and onion, belonging to Allium genus, are among the oldest food plants known since ancient times and used as ingredient of many recipes and for therapeutic properties. These plants are well known to produce bioactive apolar sulphur compounds but less is known about their polar natural compounds, such as phenols, sapogenins and saponins, that are more stable to cooking, So, we continued our work on the discovery of polar bioactive metabolites from Allium with the isolation of a number of sapogenins and saponins from the wild onion species Allium elburzense, Allium hirtifolium, Allium atroviolaceum, and Allium minutiflorum, and, more recently, from the cultivated white onion, Allium cepa, and garlic, Allium sativum. In particular, the sapogenins and saponins isolated from A. elburzense and A. hirtifolium, named elburzensosides and hirtifoliosides respectively, exhibited significant antispasmodic properties. In addition, the saponins named minutosides isolated from A. minutiflorum showed promising antimicrobial activity. More recently the phytochemical analysis of A. cepa and A. sativum has been undertaken and afforded the characterization of saponins, phenols and N-cynnamic amides which showed significant antifungal activity.     

Stemphylium leaf blight of onion

A foliar blight disease of onion (Allium cepa L.) and garlic (Allium sativum L.) hitherto unreported from India has been described from Varanasi, U. P. The infection is confined to the leaves and inflorescence stalks. The conidial stage of the pathogen is more injurious to the plants, whereas the perithecial stage occurs on the inflorescence stalks in isolated locations. The conidiophores and conidia typical of the genus Stemphylium Wallroth are formed during the early development of the disease followed by perithecia predominantly developing on the peduncles. The perithecia were also induced to develop in artificial culture and were identical in diagnostic characters to those from the field. The conidia and ascospores from both host and artificial culture were reciprocally pathogenic to onion and garlic. Morphology of the fruiting structures indicated identity of the pathogen in its conidial stage with Stemphylium vesicarium (Wallroth) Simmons and in the perithecial stage with Pleospora allii (Rabenh.) Ces. and de Not., to which they are referred respectively.     

Antithrombotic and anticancer effects of garlic-derived sulfur compounds: a review

Garlic (Allium sativum L.) has a long history as being a food having a unique taste and odor along with some medicinal qualities. Modern scientific research has revealed that the wide variety of dietary and medicinal functions of garlic can be attributed to the sulfur compounds present in or generated from garlic. Although garlic produces more than 20 kinds of sulfide compounds from a few sulfur-containing amino acids, their functions are different from one another; e.g., allicin, methyl allyl trisulfide, and diallyl trisulfide have antibacterial, antithrombotic, and anticancer activities, respectively. The present paper reviews the physiological functions of garlic in the limited study fields of its antithrombotic and anticancer effects. Before describing these effects, however, we will discuss briefly some characteristics of garlic as a plant and some modes of absorption of orally-administered sulfur compounds from garlic.     

Chemical constituents and medicinal properties of Allium species

Allium species, belonging to Alliaceae family, are among the oldest cultivated vegetables used as food. Garlic, onions, leeks and chives, which belong to this family, have been reported to have medicinal properties. The Allium species constituents have been shown to have antibacterial and antioxidant activities, and, in addition, other biological properties. These activities are related to their rich organosulfur compounds. These organosulfur compounds are believed to prevent the development of cancer, cardiovascular, neurological, diabetes, liver diseases as well as allergy and arthritis. There have also been reports on toxicities of these compounds. The major active compounds of Allium species includes, diallyl disulfide, diallyl trisulfide, diallyl sulfide, dipropyl disulfide, dipropyl trisulfide, 1-propenylpropyl disulfide, allyl methyl disulfide and dimethyl disulfide. The aim of this review is to focus on a variety of experimental and clinical reports on the effectiveness, toxicities and possible mechanisms of actions of the active compounds of garlic, onions, leek and chives.

     

Antifungal saponins from bulbs of garlic,Allium sativum L. var. Voghiera

A bioassay-guided phytochemical analysis of the polar extract from the bulbs of garlic, Allium sativum L., var. Voghiera, typical of Voghiera, Ferrara (Italy), allowed the isolation of ten furostanol saponins; voghieroside A1/A2 and voghieroside B1/B2, based on the rare agapanthagenin aglycone; voghieroside C1/C2, based on agigenin aglycone; and voghieroside D1/D2 and E1/E2, based on gitogenin aglycone. In addition, we found two known spirostanol saponins, agigenin 3-O-trisaccharide and gitogenin 3-O-tetrasaccharide. The chemical structures of the isolated compounds were established through a combination of extensive nuclear magnetic resonance, mass spectrometry and chemical analyses. High concentrations of two eugenol diglycosides were also found for the first time in Allium spp. The isolated compounds were evaluated for their antimicrobial activity towards two fungal species, the air-borne pathogen Botrytis cinerea and the antagonistic fungus Trichoderma harzianum.     

Antifungal cinnamic acid derivatives from Persian leek (Allium ampeloprasum Subsp. Persicum)

A cinnamic imidate, (1Z,2E)-methyl 3-(-p-hydroxy-m-methoxyphenyl)-N-(-p-hydroxyphenethyl) acrylimidate, named persicoimidate (1), has been isolated and characterized from bulbs and seeds of Persian leek, Allium ampeloprasum Subsp. Persicum. Two cinnamic acid derivatives, N-feruloyl tyramine (2) and N-caffeoyl tyramine (3) were isolated from bulbs and seeds. Compound 2 has been previously reported from garlic and leek, while compound 3 is described in Allium plants for the first time. The chemical structures of the isolated compounds have been elucidated unambiguously by spectroscopic methods, including 2D NMR and MS. The isolated compounds were evaluated for their antifungal activity against four fungal pathogens, the soil-borne pathogen Penicillium italicum, the air-borne pathogens Aspergillus niger and Botrytis cinerea, and the antagonistic fungi Trichoderma harzianum to evaluate the possible involvement of such compounds in resistance to pathogen attack.     

Synthesis of eco-friendly silver nanoparticles using Allium sp. and their antimicrobial potential on selected vaginal bacteria

Allium cepa and garlic Allium sativa plants were used to evaluate their potential synthesis of silver nanoparticles and their antibacterial effect on Streptococcus pneumoniae and Pseudomonas aeruginosa. Transmission electron microscopy (SEM) was used to distinguish the morphology of the nanoparticles attained from plant extracts. Energy dispersive X-ray (EDX) spectrometer established the existence of elemental sign of the silver and homogenous allocation of silver nanoparticles. Diffraction by using X ray (XRD) analysis for the formed AgNPs revealed spherical plus cubical shapes structure with different planes ranged between 111 and 311 planes. The antibacterial action of AgNPs against vaginal pathogens, Streptococcus pneumoniae and Pseudomonas aeruginosa was recognized. Our work showed a rapid, eco-safety and suitable method for the synthesis of AgNPs from Allium cepa and garlic Allium sativa extracts and can be used in biomedical applications.     

GarlicESTdb: an online database and mining tool for garlic EST sequences

Background  

Allium sativum., commonly known as garlic, is a species in the onion genus (Allium), which is a large and diverse one containing over 1,250 species. Its close relatives include chives, onion, leek and shallot. Garlic has been used throughout recorded history for culinary, medicinal use and health benefits. Currently, the interest in garlic is highly increasing due to nutritional and pharmaceutical value including high blood pressure and cholesterol, atherosclerosis and cancer. For all that, there are no comprehensive databases available for Expressed Sequence Tags(EST) of garlic for gene discovery and future efforts of genome annotation. That is why we developed a new garlic database and applications to enable comprehensive analysis of garlic gene expression.     

Floral development in bolting garlic

Garlic (Allium sativum L.) is a completely sterile plant, propagated only vegetatively. The aim of this research was to study the sequence of morphological processes occurring during floral initiation and development of a number of bolting garlic accessions from the Allium gene bank in Israel by using SEM. The garlic inflorescence is an umbel-like flower arrangement, the branches (flower clusters) of which arise from a common meristem. The numerous flowers have a distinct morphology typical of the genus Allium. Flower-stalk elongation precedes the swelling of the apical meristem and its subdivision into several centers of floral development. Within clusters, floral primordia develop unevenly. Differentiation of topsets begins after floral differentiation on the peripheral part of the apical surface, and their size, number and rate of development vary among genotypes. At least four morphological types differing in flower/topset ratio were distinguished among the 12 clones studied in this investigation. For further studies of flowering physiology and fertility restoration, only clones which can differentiate the greatest proportion of normal flowers and the least of topsets in the apical meristem should be selected. Received: 28 June 2000 / Revision accepted: 6 November 2000     

Screening of Botanical Extracts for Repellence against Western Corn Rootworm Larvae

The ability of western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) to develop resistance to various management practices requires the development of new management options. Repellent extracts can act as efficacy enhancing agents in WCR control. The present study investigated the potential repellence of garlic (Allium sativum L.), pepper (Capsicum sp. L), cape aloe (Aloe ferox Mill.), neem (Azadirachta indica A. Juss) and turmeric (Curcuma longa L.) derived extracts against WCR larvae in a no-choice bioassays. In initial screenings garlic and turmeric were evaluated as the most promising extracts as WCR larvae avoided garlic / turmeric treated soil. Turmeric was further evaluated in a rhizotron set up to quantify larval distribution and behavioral changes over time. WCR larvae avoided turmeric treated soil up to 0.05 m from its application in the root system, resulting in an increased dispersal and the formation of multiple clusters in the rhizotron. The proportion of larvae actively moving in the soil subsequently increased, whereas larval feeding significantly decreased. The spatial and behavioral alterations in the soil lead to the conclusion that turmeric is a repellent extract for WCR larvae. Turmeric repellence might further be exploited for WCR management through a synergy with insecticidal substances or microbial antagonists.     

Leek Yellow Stripe Virus Can Adjust for Host Adaptation by Trimming the N-Terminal Domain to Allow the P1 Protein to Function as an RNA Silencing Suppressor

In Japan, the P1 protein (S-type) encoded by leek yellow stripe virus (LYSV) isolates detected in Honshu and southward is shorter than the P1 (N-type) of LYSV isolates from garlic grown in Hokkaido due to a large deletion in the N-terminal half. In garlic fields in Hokkaido, two types of LYSV isolate with N- and S-type P1s are sometimes found in mixed infections. In this study, we confirmed that N- and S-type P1 sequences were present in the same plant and that they belong to different evolutionary phylogenetic groups. To investigate how LYSV with S-type P1 (LYSV-S) could have invaded LYSV with N-type P1 (LYSV-N)-infected garlic, we examined wild Allium spp. plants in Hokkaido and found that LYSV was almost undetectable. On the other hand, in Honshu, LYSV-S was detected at a high frequency in Allium spp. other than garlic, suggesting that the LYSV-S can infect a wider host range of Allium spp. compared to LYSV-N. Because P1 proteins of potyviruses have been reported to promote RNA silencing suppressor (RSS) activity of HC-Pro proteins, we analyzed whether the same was true for P1 of LYSV. In onion, contrary to expectation, the P1 protein itself had RSS activity. Moreover, the RSS activity of S-type P1 was considerably stronger than that of N-type P1, suggesting that LYSV P1 may be able to enhance its RSS activity when the deletion is in the N-terminal half and that acquiring S-type P1 may have enabled LYSV to expand its host range.     

The Global Trade in Fresh Produce and the Vagility of Plant Viruses: A Case Study in Garlic

As cuisine becomes globalized, large volumes of fresh produce are traded internationally. The potential exists for pathogens infecting fresh produce to hitchhike to new locations and perhaps to establish there. It is difficult to identify them using traditional methods if pathogens are novel, scarce, and/or unexpected. In an attempt to overcome this limitation, we used high-throughput sequencing technology as a means of detecting all RNA viruses infecting garlic (Allium sativum L.) bulbs imported into Australia from China, the USA, Mexico, Argentina and Spain, and those growing in Australia. Bulbs tested were grown over multiple vegetative generations and all were stably infected with one or more viruses, including two species not previously recorded in Australia. Present in various combinations from 10 garlic bulbs were 41 virus isolates representing potyviruses (Onion yellow dwarf virus, Leek yellow stripe virus), carlaviruses (Shallot latent virus, Garlic common latent virus) and allexiviruses (Garlic virus A, B, C, D, and X), for which 19 complete and 22 partial genome sequences were obtained, including the first complete genome sequences of two isolates of GarVD. The most genetically distinct isolates of GarVA and GarVX described so far were identified from Mexico and Argentina, and possible scenarios explaining this are presented. The complete genome sequence of an isolate of the potexvirus Asparagus virus 3 (AV3) was obtained in Australia from wild garlic (A. vineale L.), a naturalized weed. This is first time AV3 has been identified from wild garlic and the first time it has been identified beyond China and Japan. The need for routine generic diagnosis and appropriate legislation to address the risks to primary production and wild plant communities from pathogens spread through the international trade in fresh produce is discussed.     

Attempts to overcome the sterility of common garlic (Allium sativum L.)

Neither the incubation of the flower scapes of garlic (Allium sativum L.) in tetracycline solution nor the extirpation of the bulblets from the inflorescences led to the development of fertile binuclear pollen. Higher tetracycline concentrations than 125 mg per litre showed a clearly phytotoxic effect. The removal of the bulblets from the inflorescences improved the survival of flowers but it enabled only the initial stages of seed development. The seeds obtained were defective and not able to germinate. The hypothesis on infectious nature of the factors causing sterility in garlic is discussed.     

Molecular Characterization of 16S Ribosomal DNA and Phylogenetic Analysis of Two X-disease Group Phytoplasmas Affecting China-tree (Melia azedarach L.) and Garlic (Allium sativum L.) in Argentina

Two phytoplasmas closely related to the X‐disease group were associated with China‐tree (Melia azedarach L.) and garlic (Allium sativum L.) decline diseases in Argentina. The present work was aimed at studying their phylogenetic relationship based on molecular characterization of the 16S ribosomal DNA sequences. Phytoplasma DNAs were obtained from naturally infected China‐tree and garlic plants from different geographical isolates. The results from analysis of restriction fragment length polymorphisms and nucleotide sequences of the 16S rDNA showed the affiliation of China‐tree and garlic decline phytoplasmas to the 16SrIII (X‐disease group), subgroups B and J, respectively. Both organisms had high sequence similarities in the 16SrDNA nucleotide sequence with the Chayote witches’ broom phytoplasma from Brazil. The phylogenetic tree, constructed by parsimony analysis, grouped the Garlic decline, China‐tree decline, Chayote witches’ broom and Clover yellow edge phytoplasmas into a cluster separated from the other phytoplasmas of the X‐disease group.     

Characterization of chromosomal DNA and DNA polymorphism in Korean cultivars ofAllium sativum L.

The genetic background of the garlic (Allium sativum L.) is not well understood, since it is cultivated exclusively by vegetative propagation. To understand its genetic background, a local cultivar, Danyang, was chosen, and several basic characteristics of its chromosomal DNA were examined. Its G + C content was 40.6%, and the relative proportion of fast reassociated sequences, intermediate reassociated sequences, and slow reassociated sequences were 12%, 40%, and 48%, respectively. The genome size, calculated based on reassociation kinetic experiments, was 1.11 x 10¹⁰ bp or 12.16 pg per haploid genome. To compare the genetic variation among four local cultivars, Munkyung, Seosan, Euiseong, and Danyang, random amplified polymorphic DNA (RAPD) analysis was performed. By using slightly longer primers, 18–24 nucleotides in size, than the traditional primers used for such analysis, more reliable RAPD results were obtained. 15 primers gave rise to amplified bands, and the results could be grouped into two categories. The patterns of amplified products produced by 12 primers, group A, were polymorphic. These results were analyzed using a NTSYS-PC (Numerical Taxonomy and Multivariate Analysis System), and a dendrogram grouping the four local cultivars was produced. The three primers of group B gave rise to a monomorphic band pattern from four local garlic clutivars, indicating that these primers possibly recognize garlic specific sequences. These primers were useful in identifying genetic variations among theAllium species.     

Comparison of esterase isoenzyme patterns in seeds of someAllium species and in cultivars ofAllium cepa L

Esterase isoenzyme patterns were studied in seeds of 6 cultivars ofAllium cepa L. and of14 species ofAllium, namelyAllium aflatunense B. Fedtsch.,A. altaicum (Pall.) Reyse,A. Cristophii Trautv.,A. fistulosum L.,A. jajlae Vved.,A. Karsianum Fom.,A. nutans L.,A. porrum L. cv. Gigant,A. praemixtum Vved.,A. pskemense Vved.,A. ramosum L.,A.rotundum L.,A. schoenoprasum L.,A. stipitatum Regel. The cultivars differ in their isoenzyme patterns, the cultivar Ka?tická stands apart from all the other cultivars, probably due to the high alkalinity of its seed extract. The examined species, arranged according to their mutual similarity of isoenzyme patterns, form several groups corresponding to individual sections of the genus. Our results corroborate the recognizing of the sectionCepa and the subsectionPhyllodolon. The maintaining ofA. jajlae andA. rotundum as well described species fits better with our results, than degrading them to subspecies ofA. scorodoprason. Our results agree in main features with those obtained by the immunological method. Some few differences appear concerning individual species. It is evident that esterase isoenzyme patterns can be used in chemotaxonomy ofAllium on an infrageneric level, and, at least inA. cepa, also on an infraspecific level.     

Utilization of hydrolytic enzymes for the extraction of cycloalliin from garlic (Allium sativum L.)

In the present study, enzyme assisted extraction of organosulfur compounds, especially cycloalliin, from garlic (Allium sativum L.) was examined using various commercial cellulases, and the changes of the cycloalliin contents in garlic extract were investigated after storage at 40 °C and 60 °C for 30 days. Among the commercial enzymes tested, Ultraflo L showed the greatest yield of cycloalliin compared to other cellulases. The conditions were optimized to include 2.5% (v/w) addition of Ultraflo L, 1 h incubation at 40 °C and a pH of 6.0. Under the optimum conditions, the contents of cycloalliin achieved 1.5-folds increase in the enzyme-assisted garlic extract compared with the non-enzymatic extraction. In addition, the cycloalliin content was also significantly increased 3.8-fold after storage at 60 °C for 15 days. The polyphenol content was also significantly increased by 3-fold after at 60 °C for 30 days. Overall, Ultraflo L proved to be an efficient method to extract cycloalliin from garlic.