Nematicidal and allelopathic potential of Argemone mexicana,a tropical weed

Argemone mexicana L. (Papaveraceae), a tropical annual weed, is phytotoxic to many crop species. This study was designed to examine the allelochemical and nematicidal potential of A. mexicana and to better understand the role of this weed in the ecosystem. A methanol-soluble extract of the leaf material caused greater juvenile mortality of Meloidogyne javanica than did ethyl acetate or hexane extracts indicating the polar nature of the toxins. Decomposing tissues of A. mexicana in soil at 50 g kg^–1 were highly deleterious causing 80% mortality of tomato plants. At 10 g kg^–1 plant growth was enhanced, while at 30 g kg^–1 plant growth was substantially retarded. M. javanica population densities in the rhizosphere and in roots, and gall formation were significantly suppressed when 10, 30 or 50 g kg^–1 A. mexicana was allowed to decompose in the soil. To establish whether decomposition was necessary to produce phytotoxic symptoms, or whether the shoot extract alone could interfere with plant growth, an aqueous shoot extract was applied to soil. Whereas a 50% extract promoted plant growth, a 100% (100 g/500 mL distilled water) concentration significantly reduced plant height, and fresh weights of shoot and root. In general, decomposing plant material caused greater phytotoxicity compared to the aqueous extract. Addition of N as NH₄NO₃ partially alleviated the phytotoxic action of A. mexicana,and also reduced severity of root-knot disease. Adding Pseudomonas aeruginosa to soil amended with A. mexicana resulted in decreased density of M. javanicain the rhizosphere and in tomato roots, suppressed galling rates and enhanced plant growth.     

Genetic structure of drone congregations of the stingless bee Scaptotrigona mexicana

Drones of stingless bee species often form distinctive congregations of up to several hundred individuals which can persist over considerable periods of time. Here we analyse the genetic structure of three drone congregations of the neotropical stingless bee Scaptotrigona mexicana employing eight microsatellite markers. Two congregations were close to each other (50 m), the third one was located more than 10 km away from them. This spatial pattern was also reflected on the genetic level : the two close congregations did not show any population sub-structuring, whereas the more distant congregation showed a significant population differentiation to both of them. Population subdifferentiation was however low with F _st values (F _st = 0.020 and 0.014) between the distant congregations, suggesting gene flow over larger distances mediated by the drones of S. mexicana. Based on the genotypic data we also estimated the number of colonies contributing drones to the congregations. The two joint congregations consisted of drones originating from 39,6 colonies, while the third congregation was composed of drones from 21,8 colonies, thus proving that congregations of S. mexicana are constituted of unrelated drones of multicolonial origin. Received 23 April 2007; revised 21 September 2007; accepted 2 October 2007.     

Six new species ofAcourtia (Asteraceae) and a historical account ofAcourtia mexicana

Six Mexican species ofAcourtia are described. One of these novelties seems to be related toAcourtia mexicana (Lag. ex D. Don) H. Rob., whose nomenclature has been misunderstood for decades; an exhaustive literature review and examination of herbarium material supports Robinson’s combination.

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Resumen  Se describen seis nuevas especies mexicanas deAcourtia. Una de estas novedades parece estar relacionada conAcourtia mexicana (Lag. ex D. Don) H. Robinson, especie cuya nomenclatura ha sido mal interpretada por décadas; una exhaustiva revisión de la literatura así como de material de herbario, apoyan la combinación de Robinson.

     

Evaluation of Argemone mexicana for Control of Root-Infecting Fungi in Tomato

Argemone mexicana L. (Papaveraceae), a tropical annual weed, is known to be phytotoxic to many crop species. This study was designed to examine the possible impact of A. mexicana on root‐infecting fungi, changes in fungal community structure and the growth of tomato. A. mexicana decaying shoots in soil provided a marked decrease in the infectivity of Fusarium solani and Rhizoctonia solani but Macrophomina phaseolina remained unaffected. Plant height and shoot growth of tomato plants increased markedly though high concentration of A. mexicana (5% w/w) was deleterious to tomato plants. General species diversity of soil fungal communities increased in the amended soils over the controls and greater increase in diversity occurred at higher concentrations of decaying A. mexicana. Likewise, equitability and richness components of diversity increased in treatments compared to controls but declined with increasing sampling period. Aspergillus nidulans, Cephaliophora irregularis, Drechslera halodes, Paecilomyces lilacinus and Trichoderma viride were isolated exclusively from the amended soils. Aqueous extract of A. mexicana when applied in soil greatly suppressed all three of the above root‐infecting fungi, and at lower concentration actually enhanced plant growth. The influence of different levels of N‐fertilization with NH₄NO₃ on the modification of the effect of decaying A. mexicana on root‐infecting fungi was also investigated. N‐fertilization to some extent alleviated the phytotoxicity to tomato plants while suppressing the root‐infecting fungi. A. mexicana in conjunction with Pseudomonas aeruginosa, a plant growth‐promoting rhizobacterium, significantly suppressed root‐infecting fungi with concomitant increase in plant growth. Whereas P. aeruginosa was reisolated from the rhizosphere and inner root tissues of tomato, its population slightly declined in the amended soil but not to an extent that could reduce the biocontrol and growth promoting potential of the bacterium.     

Sporoderm development inNymphaea mexicana (Nymphaeaceae)

Mature pollen grains ofNymphaea mexicana have a verrucate proximal surface, a psilate distal surface and an anazonasulculus (encircling-sulcate aperture). The developmental events of microspores and tapetal cells were observed with TEM and SEM. Radially oriented substructural elements are seen in the microspore surface coating ofNymphaea mexicana from the early tetrad stage through the whole exine development. These elements, being the structural units of the microspore surface matrix (glycocalyx), are associated with sporopollenin precursor accumulation. In young free microspores, radially oriented elements are observed at both proximal and distal poles as a palisade between the endexine and plasmalemma.—Several points are discussed: (1) the initial and mature forms of exine substructure elements; (2) the significance of exine substructure for realisation of morphogenetic processes; (3) the ways by which verrucate and psilate sculpture patterns are developed.     

Development and cross-species testing of western bluebird (Sialia mexicana) microsatellite primers

Western and eastern bluebirds (Sialia mexicana and S. sialis) are socially monogamous passerines that engage in extra‐pair copulations. We obtained microsatellites from S. mexicana and optimized and characterized 15 microsatellite DNA loci in 60 individuals of this species. Primer pairs yielded an average of 13 alleles per locus in western bluebirds (range 3–35 alleles) with an average observed heterozygosity of 0.68 (range 0.27–0.88). All 15 loci also successfully amplified in S. sialis (n = 24), with an average of 11.5 alleles per locus (range 4–26) and an average observed heterozygosity of 0.59 (range 0.22–0.90).     

Comparative chemical composition of Agastache mexicana subsp. mexicana and A. mexicana subsp. xolocotziana

A comparative chemical analysis of Agastache mexicana subsp. mexicana and A. mexicana subsp. xolocotziana reveals that their methanol extracts constituents were very similar, with acacetin and (2-acetyl)-7-O-glucosyl acacetin being the most abundant compounds obtained. These results are consistent with the information reported for other species of Agastache. However, GS-MS analyses showed that methyl chavicol, limonene and linalool were the main constituents of the essential oils of A. mexicana subsp. mexicana, while pulegone, menthone and isopulegone were the major constituents found in A. mexicana subsp. xolocotziana. Furthermore, a different composition was found in their respective hexane extracts. These chemical composition dissimilarities between the two taxa support their recognition as distinct subspecies.     

Phytophthora-Stammbasisfäule an Dieffenbachia maculate (Erreger: P. mexicana Hots. et Hart.)

Stem base rot of Dieffenbachia maculata caused by Phytophthora mexicana During the last years a stem rot of Dieffenbachia maculata (Lodd.) G. Don has been observed in greenhouses of several commercial nurseries, located in different parts of the Federal Republic of Germany. The disease partly caused heavy losses. From all diseased plant parts (stem base, petiole and root) the same fungus could be isolated. It was diagnosed as Phytophthora mexicana Hots, et Hart., which is closely related to P. palmivora (Butl.) Butl. Apparently the former species is recorded for the first time as the causal organism of a Dieffenbachia stem rot and also for the first time in Europe. It is supposed that the fungus was imported to Germany via the Netherlands because all plants had been bought there, which diseased later.     

Developmental sequence for the copulatory organs of Kontikia mexicana with remarks on taxonomic significance (Turbellaria: Tricladida: Geoplanidae)

Five specimens, presumably representing different developmental stages of the land planarian Kontikia mexicana (Hyman, 1939), were used to reconstruct the development of the copulatory apparatus in this species. The results support the notion that Kontikia differs from the closely related Caenoplana in its possession of a penis papilla. In the earliest stage available, a penis papilla was absent and other components were not differentiated. In a late-juvenile condition, the gonopore, seminal vesicle, and ejaculatory duct were present. The short penis papilla appeared to arise in this stage by elongation of the terminal tissue around the ejaculatory duct and its separation from the antral wall. The female canal was guarded by an epithelial fold and the glandular duct was present. In the mature condition, the penis papilla was more elongate, and the secretory (prostatic) region of the ejaculatory duct was functional. The female canal, guarded by an epithelial fold, was well-developed with enlarged glandular duct but lacking the posterior diverticulum and the sperm storage system associated with the ovovitelline ducts known in Kontikia orana Froehlich, 1955.     

Leishmania (L.) mexicana Infected Bats in Mexico: Novel Potential Reservoirs

Leishmania (Leishmania) mexicana causes cutaneous leishmaniasis, an endemic zoonosis affecting a growing number of patients in the southeastern states of Mexico. Some foci are found in shade-grown cocoa and coffee plantations, or near perennial forests that provide rich breeding grounds for the sand fly vectors, but also harbor a variety of bat species that live off the abundant fruits provided by these shade-giving trees. The close proximity between sand flies and bats makes their interaction feasible, yet bats infected with Leishmania (L.) mexicana have not been reported. Here we analyzed 420 bats from six states of Mexico that had reported patients with leishmaniasis. Tissues of bats, including skin, heart, liver and/or spleen were screened by PCR for Leishmania (L.) mexicana DNA. We found that 41 bats (9.77%), belonging to 13 species, showed positive PCR results in various tissues. The infected tissues showed no evidence of macroscopic lesions. Of the infected bats, 12 species were frugivorous, insectivorous or nectarivorous, and only one species was sanguivorous (Desmodus rotundus), and most of them belonged to the family Phyllostomidae. The eco-region where most of the infected bats were caught is the Gulf Coastal Plain of Chiapas and Tabasco. Through experimental infections of two Tadarida brasiliensis bats in captivity, we show that this species can harbor viable, infective Leishmania (L.) mexicana parasites that are capable of infecting BALB/c mice. We conclude that various species of bats belonging to the family Phyllostomidae are possible reservoir hosts for Leishmania (L.) mexicana, if it can be shown that such bats are infective for the sand fly vector. Further studies are needed to determine how these bats become infected, how long the parasite remains viable inside these potential hosts and whether they are infective to sand flies to fully evaluate their impact on disease epidemiology.     

Comparative karyotype analysis ofCeratozamia mexicana andMicrocycas calocoma (Zamiaceae) using fluorochrome banding (CMA/DAPI) and fluorescence in situ hybridization of ribosomal DNA

Orcein staining, differential staining with CMA and DAPI, and FISH with an rDNA probe were used to compare somatic chromosomes ofCeratozamia mexicana andMicrocycas calocoma. CMA-positive dots and hybridization signals appeared on chromosomes at early interphase and mitotic prophase, but in significantly different number in the two species. InCeratozamia mexicana, the CMA-positive and DAPI-negative bands and the hybridization signal were located at the terminal region of the long arm of three median-centromeric chromosomes, the terminal region of the short arm of two median-centromeric chromosomes and the terminal region of the long arm of two subterminal-centromeric chromosomes. InMicrocycas calocoma, they were located at the pericentric region of two median-centromeric chromosomes. These chromosome data suggested thatMicrocycas has no simple Robertsonian relationship toCeratozamia.     

A new and morphologically distinct population of cavernicolous Poecilia mexicana (Poeciliidae: Teleostei)

The cave molly, Poecilia mexicana, from the Cueva del Azufre, a sulfur cave in Tabasco, Mexico, ranks among the best-studied cave fishes worldwide, despite being known from a single population only. Here we describe a newly discovered second population of cave-dwelling P. mexicana from a nearby, but mostly non-sulfidic cave (Luna Azufre). Despite apparent similarities between the two populations (such as reduced eye diameter and reduced pigmentation), a geometric morphometric analysis revealed pronounced morphological differentiation between the two cave forms.     

Differential phagocytosis of Leishmania mexicana promastigotes and amastigotes by monocyte‐derived dendritic cells

Leishmania species are dimorphic protozoan parasites that live and replicate in the gut of sand flies as promastigotes or in mammalian hosts as amastigotes. Different immune cells, including DCs, and receptors differ in their involvement in phagocytosis of promastigotes and amastigotes and in recognition of different Leishmania species. In the case of L. mexicana, differences in phagocytosis of promastigotes and amastigotes by DCs and participation of C‐type lectin receptors (CLRs) have not been established. In the present study, flow cytometry and confocal microscopy were used to investigate the phagocytosis by monocyte‐derived dendritic cells (moDCs) of L. mexicana promastigotes and amastigotes in the presence or absence of immune serum during various periods of time. Blocking antibodies against mannose receptors and DC‐SIGN were used to explore the participation of these receptors in the phagocytosis of L. mexicana by moDC. The major differences in interactions of L. mexicana promastigotes and amastigotes with moDC were found to occur within the first 3 hr, during which phagocytosis of promastigotes predominated as compared with opsonization of promastigotes and amastigotes. However, after 6 hr of incubation, opsonized promastigotes were preferentially phagocytosed as compared with unopsonized promastigotes and amastigotes and after 24 hr of incubation there were no differences in the phagocytosis of promastigotes and amastigotes. Finally, after 3 hr incubation, DC‐SIGN was involved in the phagocytosis of promastigotes, but not of amastigotes.     

Partial characterization of an antheridiogen of Anemia mexicana: Comparison with the antheridiogen of A. phyllitidis

An antheridiogen of Anemia mexicana Klotzsch has been partially characterized by combined gas chromatography-mass spectrometry and gas chromatography-Fourier transform/infra-red spectrometry. It is a C₁₉-gibberellin(GA)-like compound with one carboxyl group, an exocyclic methylene group and a lactone ring. It also has one hydroxyl-group and one double-bond equivalent which has not been determined. On the basis of its mass spectrum, it is not identical to previously identified monohydroxy GAs with one ring double bond such as GA₅, GA₇, GA₃₁ and GA₆₂. By direct comparison of mass spectra, the antheridiogen of A. mexicana was also determined to be different from the antheridiogens of Anemia phyllitidis (L.) Swartz, Anemia hirsuta (L.) Swartz and Lygodium japonicum (Thunb.) Sw.Abbreviations GA(s) gibberellin(s) - GA_a gibberellin A_n - GC-FT/IR combined gas chromatography-Fourier transform/infra-red spectrometry - GC-MS combined gas chromatography-mass spectrometry - IR intra-red spectrometry - KRI Kovats Retention Index - m/z mass/charge - TLC thin-layer chromatography - TMSi trimethylsilyl     

Somatic embryogenesis from leaf callus of mature plants of the gymnospermCeratozamia mexicana var. robusta (Miq.) dyer (Cycadales)

Summary Embryogenic callus was induced from explanted pinnae of newly emerged leaves of mature plants ofCeratozamia mexicana var. Robusta (Gymnospermae, Cycadales) on a modified B5 formulation with 1 mg·liter⁻¹ kinetin and 1 mg·liter⁻¹ 2,4-dichlorophenoxyacetic acid. Proembryos developed on induction medium, but they were more numerous after subculture onto phytohormone-free medium, which also enabled suspensors to elongate. For nearly 1.5 yr after explanting, subsequent development of somatic embryos was not observed as suspensors dedifferentiated to form embryogenic callus on phytohormone-free medium. After this time, cotyledonary somatic embryos developed at the distal end of the suspensors. Somatic embryos have germinated on phytohormone-free medium. This is the first report of regeneration by somatic embryogenesis of a gymnosperm species from a mature tree. This technique has great potential for preservation of the highly endangered cycads.     

Sexual and Aggressive Behaviour in Species Hybrids of Poecilia mexicana and Poecilia velifera (Pisces,Poeciliidae)

The inheritance of sexual behaviour patterns was studied in species hybrids of Poecilia mexicana and Poecilia velifera. In addition, the aggressive behaviour and some morphological characters have been investigated and checked for a possible correlation between and within these three different traits studied. All the characters are inherited polygenically. The minimum genetic factors could be estimated only for some characters.     

Atta mexicana waste dumps are hot spots of soil nutrients in an urban Neotropical cloud forest environment

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Phenology of Paralemanea mexicana (Batrachospermales,Rhodophyta) in a high‐altitude stream in central Mexico

The morphology and phenology of Paralemanea mexicana (Kützing) Vis et Sheath was evaluated seasonally in a fifth order high‐altitude stream in central Mexico. The gametophytes grew during oligotrophic and eutrophic conditions, and during particular microhabitat conditions: high current velocity (40–240 cm s^?1), low to medium irradiance (5–973 μmol photons m^?2 s^?1), and shallow depth (1–30 cm). The abundance of gametophytes was positively correlated with low temperature, high current velocity and concentrations of soluble reactive phosphorus. Interestingly, monoecious gametophytes formed two types of branches, true branches with sympodial pattern originating from meristematic cells in variable number, and abundant false branches produced during the development of the ‘Chantransia’ stage in the surface of the gametophyte or by uniseriate filaments arising within the thallus lumen. These filaments generally produce gametophytes and suggest that they could support the germination of carpospores. The frequently whorled branches are the result of a false branching pattern and are exclusive to P. mexicana. These morphological and reproductive characteristics appear to be biomechanical adaptations to avoid detachment and increase reproductive success. Efficient reproductive strategies of P. mexicana observed in this study can be interpreted as adaptations to successfully colonize streams; however, these features may not have been common in the study region due to restricted microhabitat conditions and geographic isolation.     

Leishmania tropica and Leishmania mexicana: cross-immunity in mice

The effect of a previous or concurrent Leishmania tropica major infection on a L. mexicana infection was studied. Mice which were recovering from or had recovered from a L. tropica infection were found to be totally resistant to L. mexicana. Infection of mice already carrying a L. mexicana infection with L. tropica resulted in subsequent ulceration and eventual healing of the lesions caused by both Leishmania species. Mice infected with L. mexicana were found normally to be no more susceptible to L. tropica than untreated mice: Only when L. tropica infections were located in the region of a draining lymph node already serving a L. mexicana infection did lesions of the former parasite persist.     

Fate of epiphytes on phorophytes with different architectural characteristics along the perturbation gradient of Sabal mexicana forests in Veracruz,Mexico

Question: Vascular epiphytes and hemiepiphytes (E/HE) in neotropical forests account for a large fraction of plant richness, but little is known of how the interplay between phorophyte architectural characteristics and habitat perturbation affect communities of E/HE. Location: Sabal mexicana forests in a coastal area of Veracruz, Mexico. Methods: We compared communities of E/HE on phorophytes with different architectural characteristics – the palm S. mexicana and non‐palm phorophytes – in three environments: conserved sites, perturbed sites and small regenerated forest fragments. We combined traditional (abundance, species richness, similarity and complementarity indices) and more recent (phylogenetic diversity) metrics to describe the communities of E/HE. Results: Overall, we recorded 924 E/HE individuals (nine families, 16 genera and 21 species). The abundance and species richness of E/HE was higher on palms than on non‐palm phorophytes. Abundance‐based complementarities between phorophytes and sites were high. We detected clear changes in community structure of E/HE with habitat perturbation, but there were no effects on the phylogenetic diversity of the E/HE community. Palm phorophytes hosted a more phylogenetically diverse community of E/HE than did non‐palm phorophytes. Conclusions: Palm phorophytes are key elements supporting the conservation of resilient communities of E/HE in S. mexicana forest. Habitat fragmentation has a strong effect on the structure of the E/HE community in S. mexicana forests. Ferns are the group of epiphytes most severely affected by habitat perturbation, but we detected no significant effect on the phylogenetic diversity of the community.