Anatomical and chemical characterization of leaves from <em>Oreopanax</em> spp. (Araliaceae), the Mexican xoco tamale food complex

Background: Based on the concept of “plant species complex,”, defined as a group sharing local names and morphological, aromatic, and curative properties, we analyzed the leaves of three species of the genus Oreopanax that are used as wrappers for tamales called “xocos” or “chocos” in Veracruz, Mexico, searching for common traits. Question: Do leaves of the genus Oreopanax form an ethnobotanical food complex sharing chemical and anatomical characteristics? Studied species / data description: Leaves from three species of the genus Oreopanax: O. capitatus, O. echinops, and O. flaccidus. Study site and dates: Leaves of O. capitatus and O. echinops were recollected on January 25 and 26, 2021, in the Clavijero Botanic Garden of the Instituto de Ecología, A. C. in Xalapa, Veracruz; leaves of O. flaccidus were recollected in Atapalchico, Tlacolulan, Veracruz. Methods: Chemical analyses consisted of oil extraction of the studied species' leaves, which were then injected into a gas chromatographer coupled to a mass spectrometer (GC-MS). Anatomical analyses included: fixation, paraffin sectioning, and staining of leaf sections of the three species. Observations were performed with a compound microscope using a bright field or UV light. Results: For the first time, we are reporting major volatile compounds common in the three analyzed species (several aliphatic and aromatic alcohols, and terpenoids). The three species present resin canals in the mesophyll and the cortex of the midrib of the leaf. Conclusions: The studied Oreopanax species form an ethnobotanical food complex since they share similar uses, smells, and tastes

Biocontrol and plant growth promoting traits of two avocado rhizobacteria are orchestrated by the emission of diffusible and volatile compounds

Avocado (Persea americana Mill.) is a tree crop of great social and economic importance. However, the crop productivity is hindered by fast-spreading diseases, which calls for the search of new biocontrol alternatives to mitigate the impact of avocado phytopathogens. Our objectives were to evaluate the antimicrobial activity of diffusible and volatile organic compounds (VOCs) produced by two avocado rhizobacteria (Bacillus A8a and HA) against phytopathogens Fusarium solani, Fusarium kuroshium, and Phytophthora cinnamomi, and assess their plant growth promoting effect in Arabidopsis thaliana. We found that, in vitro, VOCs emitted by both bacterial strains inhibited mycelial growth of the tested pathogens by at least 20%. Identification of bacterial VOCs by gas chromatography coupled to mass spectrometry (GC–MS) showed a predominance of ketones, alcohols and nitrogenous compounds, previously reported for their antimicrobial activity. Bacterial organic extracts obtained with ethyl acetate significantly reduced mycelial growth of F. solani, F. kuroshium, and P. cinnamomi, the highest inhibition being displayed by those from strain A8a (32, 77, and 100% inhibition, respectively). Tentative identifications carried out by liquid chromatography coupled to accurate mass spectrometry of diffusible metabolites in the bacterial extracts, evidenced the presence of some polyketides such as macrolactins and difficidin, hybrid peptides including bacillaene, and non-ribosomal peptides such as bacilysin, which have also been described in Bacillus spp. for antimicrobial activities. The plant growth regulator indole-3-acetic acid was also identified in the bacterial extracts. In vitro assays showed that VOCs from strain HA and diffusible compounds from strain A8a modified root development and increased fresh weight of A. thaliana. These compounds differentially activated several hormonal signaling pathways involved in development and defense responses in A. thaliana, such as auxin, jasmonic acid (JA) and salicylic acid (SA); genetic analyses suggested that developmental stimulation of the root system architecture by strain A8a was mediated by the auxin signaling pathway. Furthermore, both strains were able to enhance plant growth and decreased the symptoms of Fusarium wilt in A. thaliana when soil-inoculated. Collectively, our results evidence the potential of these two rhizobacterial strains and their metabolites as biocontrol agents of avocado pathogens and as biofertilizers

Electroantennographic Responses of Wild and Laboratory-Reared Females of Xyleborus affinis Eichhoff and Xyleborus ferrugineus (Fabricius) (Coleoptera: Curculionidae: Scolytinae) to Ethanol and Bark Volatiles of Three Host-Plant Species

Chemical ecology studies on ambrosia beetles are typically conducted with either wild or laboratory-reared specimens. Unlike laboratory-reared insects, important aspects that potentially influence behavioral responses, such as age, physiological state, and prior experience are unknown in wild specimens. In this study, we compared the electroantennographic (EAG) responses of laboratory-reared and wild X. affinis and X. ferrugineus to 70% ethanol and bark odors (host kairomones) of Bursera simaruba, Mangifera indica, and Persea schiedeana aged for 2, 24, and 48 h. Chemical analyses of each odor treatment (bark species x length of aging) were performed to determine their volatilome composition. EAG responses were different between laboratory-reared and wild X. ferrugineus when exposed to ethanol, whereas wild X. affinis exhibited similar EAG responses to the laboratory-reared insects. Ethanol elicited the strongest olfactory responses in both species. Among the bark-odors, the highest responses were triggered by B. simaruba at 48 h in X. affinis, and P. schiedeana at 24 and 48 h in X. ferrugineus. Volatile profiles varied among aged bark samples; 3-carene and limonene were predominant in B. simaruba, whereas &alpha;-copaene and &alpha;-cubebene were abundant in P. schiedeana. Further studies are needed to determine the biological function of B. simaruba and P. schiedeana terpenes on X. affinis and X. ferrugineus, and their potential application for the development of effective lures

Plant growth-promoting rhizobacteria associated with avocado display antagonistic activity against <i>Phytophthora cinnamomi</i> through volatile emissions

<div><p>Rhizobacteria associated with crops constitute an important source of potentially beneficial microorganisms with plant growth promoting activity or antagonistic effects against phytopathogens. In this study, we evaluated the plant growth promoting activity of 11 bacterial isolates that were obtained from the rhizosphere of healthy avocado trees and from that of avocado trees having survived root rot infestations. Seven bacterial isolates, belonging to the genera <i>Bacillus</i>, <i>Pseudomonas</i> and <i>Arthrobacter</i>, promoted <i>in vitro</i> growth of <i>Arabidopsis thaliana</i>. These isolates were then tested for antagonistic activity against <i>Phytophthora cinnamomi</i>, in direct dual culture assays. Two of those rhizobacterial isolates, obtained from symptomatic-declining trees, displayed antagonistic activity. Isolate A8a, which is closely related to <i>Bacillus acidiceler</i>, was also able to inhibit <i>P</i>. <i>cinnamomi</i> growth <i>in vitro</i> by 76% through the production of volatile compounds. Solid phase microextraction (SPME) and analysis by gas chromatography coupled with mass spectrometry (GC-MS) allowed to tentatively identify the main volatiles emitted by isolate A8a as 2,3,5-trimethylpyrazine, 6,10-dimethyl-5,9-undecadien-2-one and 3-amino-1,3-oxazolidin-2-one. These volatile compounds have been reported to show antifungal activity when produced by other bacterial isolates. These results confirm the significance of rhizobacteria and suggest that these bacteria could be used for biocontrol of soil borne oomycetes through their volatiles emissions.</p></div

Co-cultivation of <i>Arabidopsis thaliana</i> seedlings with rhizobacterial isolates from symptomatic-declining avocado trees.

<p>Representative photographs of Arabidopsis Col-0 seedlings transferred to non-inoculated (Control) fresh media, or inoculated with rhizobacterial isolates at 2.5 cm (long distance) and 1 cm (close distance) from root tip. Primary root length (b), lateral root number (c) and fresh weight accumulation (d) were the developmental parameters analyzed. Data values represent the mean of 30 seedlings ± SE per treatment; different letters in graphs indicate significant differences (<i>P</i> < 0.05).</p

Antagonical activity of isolate A8a, phylogenetically close to <i>Bacillus acidiceler</i>, against <i>Phytophthora cinnamomi</i>.

<p>Disks of <i>P</i>. <i>cinnamomi</i> mycelium were grown on agar PDA-containing plates. Radial growth was monitored for 11 days in non-inoculated conditions (a). Confrontation with <i>B</i>. <i>acidiceler</i> was performed by directly co-cultivating mycelial disks with bacterial inoculum, at a distance of 2 cm (b), or indirectly, growing them on the opposite halves of the same Petri dish (c). Assays were carried out by triplicate. Representative plates were photographed at day 5 and 11 after inoculation (dai). At 7 dai, the inhibition percentage of mycelial radial growth by direct (light gray bars) or indirect (dark gray bars) antagonism was analyzed (d); hyphal deformations induced by indirect inoculation were visually analyzed by stereoscopic observations at 7 dai (e). Values shown in (d) represent the mean of three replicates ± SD; asterisks indicate significant inhibition (<i>P</i> ≤ 0.05).</p

Localization and characteristics of sampling site.

<p>Geographic projection of Veracruz state and the Municipality of Huatusco (a); view of sampling zones (b), the symptomatic zone A is surrounded by yellow ovals; a representative healthy or symptomatic-declining tree is shown (c, d); map (a) was created using ArcMap 10.2.2. The authors generated digital information such as polygons and contours (public domain).</p

Maximum-Likelihood tree of partially sequenced 16S rRNA genes.

<p>Bold letters indicate rhizobacterial isolates that were obtained in this study. Values above nodes are bootstrap values obtained from 1000 replicates.</p

Molecular identification of avocado rhizobacteria with plant growth promoting activity by 16S rRNA sequencing.

<p>Taxonomic assignment was determined with the rdp classifier tool. Sequence closest matches were based on the NCBI database “16S ribosomal RNA sequences (Bacteria and Archaea)”.</p

Direct antagonism assays of avocado rhizobacteria against <i>Phytophthora cinnamomi</i>.

<p>Mycelial growth was measured at fifth day after dual culture.</p