Effects of the fungus Pestalotiopsis maculans (Ascomycota: Amphisphaeriales) on the gametophytic development of the fern Lygodium venustum (Lygodiaceae)

Lygodium Sw. is the only genus of the family Lygodiaceae, with around 25 to 40 species inhabiting mostly tropical regions worldwide. In Argentina two species develop; one of them, L. venustum, grows in the Northeast of the country. Some species of Lygodium are invasive whereas medicinal uses have been reported for some taxa. As part of a project to ascertain on the reproductive biology of native ferns in Argentina, a fungus was found during in vitro spore culture of L. venustum. Dark brown spots and eruptive pustules were also observed in fertile leaves. Thus, emerged as objectives of this work: 1) to retrieve and identify the fungus from the sporophyte and from the spores cultures, 2) to inquire on the impact of the fungus on gametophyte generation, and 3) to perform experiments with untreated spores to demonstrate that the fungus is associated to the spores collected from infested sporophytes. Phytopathological techniques were applied in order to isolate the fungus and then to achieve monosporic cultures. The morpho-biometric features of the conidia corresponded with those of Pestalotiopsis maculans (Corda) Nag Raj [= Pestalotiopsis guepinii (Desm.) Steyaert] (Amphisphaeriales, Ascomycota). Re-inoculation of conidia on healthy gametophytes conducted to their necrosis and death. The percentages of spore germination were initially higher in unsterilized cultures, suggesting that disinfection protocol may have affected spore germination. This is the first report of Pestalotiopsis maculans on the sporophytes of Lygodium venustum. The information that emerges from our work could be useful for the biocontrol of other species of Lygodium, considered weeds in other regions of the world.

Efectos del hongo Pestalotiopsis maculans (Ascomycota: Amphisphaeriales) en el desarrollo gametofítico del helecho Lygodium venustum (Lygodiaceae). Lygodium Sw. es el único género de la familia Lygodiaceae, con alrededor de 25 a 40 especies que habitan en su mayoría en regiones tropicales del mundo. En Argentina se desarrollan dos especies; uno de ellas, L. venustum, crece en el noreste del país. Algunas especies de Lygodium son invasivas, mientras que para algunos taxones se han reportado usos medicinales. Como parte de un proyecto para indagar sobre la biología reproductiva de los helechos nativos en Argentina, se encontró un hongo durante el cultivo in vitro de esporas de L. venustum. Asimismo, se observaron manchas marrones oscuras y pústulas eruptivas en hojas fértiles. Así, surgieron como objetivos de este trabajo: 1) recuperar e identificar el hongo presente en el esporofito y en los cultivos de esporas, 2) investigar el impacto del hongo en la generación gametofítica y 3) realizar experimentos con esporas no tratadas para demostrar que el hongo está asociado a las esporas recolectadas de esporofitos infestados. Se aplicaron técnicas fitopatológicas para aislar el hongo y luego lograr cultivos monospóricos. Las características morfo-biométricas de los conidios correspondieron a las de Pestalotiopsis maculans (Corda) Nag Raj [= Pestalotiopsis guepinii (Desm.) Steyaert] (Amphisphaeriales, Ascomycota). La re-inoculación de conidios en gametofitos sanos condujo a su necrosis y muerte. Los porcentajes de germinación de esporas fueron inicialmente más altos en los cultivos no esterilizados, lo que sugiere que el protocolo de desinfección pudo haber afectado la germinación de las esporas. Este es el primer reporte de Pestalotiopsis maculans sobre los esporofitos de Lygodium venustum. La información que surge de nuestro trabajo podría ser útil para el control biológico de otras especies de Lygodium, consideradas malezas en otras regiones del mundo.

Morfogénesis de la fase sexual de los helechos epífitos Microgramma mortoniana y Pleopeltis macrocarpa (Polypodiaceae) de la Reserva Natural Punta Lara, Buenos Aires, Argentina / Sexual morphogenesis phase of the epiphytic ferns Microgramma mortoniana and Pleopeltis macrocarpa (Polypodiaceae) from Punta Lara Natural Reserve, Buenos Aires, Argentina

Resumen Pleopeltis macrocarpa y Microgramma mortoniana son dos helechos epífitos de la familia Polypodiaceae hallados con baja frecuencia en la Reserva Natural Punta Lara (Buenos Aires, Argentina). El objetivo de este trabajo fue estudiar la morfogénesis de gametófitos epífitos para fortalecer poblaciones vulnerables y contribuir a su conservación. Se recolectaron hojas fértiles. Las esporas se sembraron en placas de Petri con medio de cultivo Dyer. Las esporas se caracterizaron por ser monoletes, elipsoidales, amarillentas y con ornamentación verrucosa. La germinación fue del tipo Vittaria y el desarrollo del gametofito es del tipo Drynaria. El esporofito de P. macrocarpa surgió a los 500 días y el de M. mortoniana a los 120. El patrón de germinación, el desarrollo del gametofito, el glóbulo lipídico en la célula protálica y los pelos unicelulares capitados en el margen podrían considerarse en la sistemática del grupo. La demora en la formación de esporofitos a través de la reproducción sexual, permite inferir que el éxito de su propagación estaría sujeto a la reproducción vegetativa.

Abstract The Punta Lara Natural Reserve is located on the riverside of the La Plata River in the province of Buenos Aires, Argentina. It is the Southernmost relict in the world of subtropical riparian forest. The epiphytic ferns studied in this work belong to the Polypodiaceae family: Microgramma mortoniana and Pleopeltis macrocarpa. Plant communities are subject to high levels of anthropization and introduction of exotic species. The goals of this work are to provide information on the morphogenesis of epiphytic gametophytes and to extend knowledge of their life cycles, contributing to their conservation. Sowing was carried out in Dyer medium. In both species the spores are monolete, ellipsoidal, yellowish and with verrucate sculpture. The equatorial diameter is 60-61 μm, the polar diameter is 39-42 μm. The germination is the Vittaria type; in M. mortoniana occurs at 20 days, while in P. macrocarpa occurs at six days. The filaments are uniseriate of 3-6 cells in length. The gametophyte development is Drynaria type. The cordated form is given after 40 days. In M. mortoniana, buds originated after 40 days. In P. macrocarpa, after 120 days, clathrate trichomes scale-like appear mainly on the margins of the gametophyte. The gametangia are typical of leptosporangiate ferns. The sporophyte of M. mortoniana emerged after 120 days and that of P. macrocarpa arose after 500 days, its blades are simple, spatulate and unicellular and multicellular branching hairs were observed. The germination pattern, gametophyte development, the presence of a lipid globule in the prothalic cell and the formation of unicellular capitated hairs are relevant characters that could be considered for systematic group. The delay in the formation of sporophytes through sexual reproduction, allows us to infer that the success of their establishment in situ would be given by the vegetative reproduction through creeping rhizomes and buds of gametophytes. Rev. Biol. Trop. 66(3): 1078-1089. Epub 2018 September 01.

In vitro propagation of Cyathea atrovirens (Cyatheaceae): spore storage and sterilization conditions / Propagación in vitro de Cyathea atrovirens (Cyatheaceae): almacenamiento de esporas y condiciones de esterilización

Cyathea atrovirens occurs in a wide range of habitats in Brazil, Paraguay, Uruguay and Argentina. In the Brazilian State of Rio Grande do Sul, this commonly found species is a target of intense exploitation, because of its ornamental characteristics. The in vitro cultura is an important tool for propagation which may contribute toward the reduction of extractivism. However, exogenous contamination of spores is an obstacle for the success of aseptic long-term cultures. This study evaluated the influence of different sterilization methods combined with storage conditions on the contamination of the in vitro cultures and the gametophytic development of C. atrovirens, in order to establish an efficient propagation protocol. Spores were obtained from plants collected in Novo Hamburgo, State of Rio Grande do Sul, Brazil. In the first experiment, spores stored at 7oC were surface sterilized with 0.5, 0.8 and 2% of sodium hypochlorite (NaClO) for 15 minutes and sown in Meyer’s culture medium. The cultures were maintained in a growth room at 26±1ºC for a 12-h photoperiod and photon flux density of 100μmol/m²/s provided by cool white fluorescent light. Contamination was assessed at 60 days, and gametophytic development was scored at 30, 60, 120 and 130 days of in vitro culture, analyzing 300 individuals for each treatment. There was no significant difference in culture contamination among the different sodium hypochlorite concentrations tested, and all treatments allowed for the development of cordiform gametophytes at 130 days of culture. In the second experiment, spores stored at 7 and -20°C were divided into two groups. Half of the spores were surface sterilized with 2% of NaClO for 15 minutes and the other half was not sterilized. All spores were sown in Meyer’s medium supplemented with one of the following antibiotics: nystatin, Micostatin® and actidione. The culture conditions and the procedures used for evaluating contamination and gametophytic development were the same described for the first experiment. No contamination was observed in spores stored at -20°C and treated with NaClO and actidione. In all treatments, cordiform gametophytes presenting antheridia were observed at 120 days. The percentages of these gametophytes increased from 120 to 130 days and no significant differences were observed among treatments. Archegonia were observed on cordiform gametophytes at 130 days. The findings provide data relevant to in vitro propagation procedures of this species, which may increase the availability of plants for ornamental purposes, therefore contributing to the reduction of the exploitation of endangered tree ferns species. Rev. Biol. Trop. 62 (1): 299-308. Epub 2014 March 01.

Cyathea atrovirens (Langsd. & Fisch.) Domin (Cyatheaceae) se presenta en una amplia gama de hábitats en Brasil, Paraguay, Uruguay y Argentina. Debido a sus características ornamentales, la especie es objeto de intensa explotación. El cultivo in vitro es una herramienta importante para la propagación lo que puede contribuir a la reducción del impacto de las actividades extractivas. Sin embargo, la contaminación exógena de esporas es un obstáculo para el éxito de cultivos asépticos a largo plazo. Este estudio evaluó la influencia de diferentes métodos de esterilización en combinación con las condiciones de almacenamiento sobre la contaminación de los cultivos in vitro y el desarrollo gametofítico de C. atrovirens. En el primer experimento, las esporas almacenadas a 7°C se esterilizaron superficialmente con 0.5, 0.8 y 2% de hipoclorito de sodio (NaClO) durante 15 minutos y se sembraron en medio de cultivo de Meyer. Aunque no hubo diferencia en la contaminación de lós cultivos entre las concentraciones de hipoclorito de sodio de las diferentes pruebas, en el tratamiento con 2% NaClO se observó un mayor porcentaje de gametofitos cordiformes a los 130 días. En el segundo experimento, las esporas almacenadas a 7 y -20°C fueron divididas en dos grupos. La mitad de las esporas se esterilizaron con 2% de NaClO durante 15 minutos y la otra mitad no fue esterilizada. Todas las esporas se sembraron en medio de Meyer suplementado con uno de los siguientes antibióticos: nistatina, Micostatin® o actidiona. No se observó contaminación de las esporas almacenadas a -20°C y tratadas con NaClO y actidiona. En todos los tratamientos, se observaron gametofitos cordiformes con anteridios y arquegonios. Los resultados proporcionan datos relevantes para la propagación in vitro de C. atrovirens, que pueden aumentar la disponibilidad de las plantas para fines ornamentales, contribuyendo así a la reducción de la exploración de las especies de helechos arborescentes en peligro de extinción.

Mycorrhizal association in gametophytes and sporophytes of the fern Pteris vittata (Pteridaceae) with Glomus intraradices

Ferns, which are usually colonizing different environments and their roots frequently present mycorrhization, have two adult stages in their life cycle, the sporophytic and the gametophytic phase. This paper describes the experimental mycorrhizal association between Pteris vittata leptosporangiate fern and a strain of Glomus intraradices during the life cycle of the fern, from spore germination to the development of a mature sporophyte. The aim of this study was to compare the colonization pattern of in vitro cultures of G. intraradices along the fern life cycle with those found in nature. For this, mature spores were obtained from fertile P. vittata fronds growing in walls of Buenos Aires city, Argentina. Roots were stained and observed under the light microscope for arbuscular mycorrhizal colonization. Approximately, 75 fern spores were cultured in each pot filled with a sterile substrate and G. intraradices (BAFC N° 51.331) as inoculum on the surface. After germination took place, samples were taken every 15 days until the fern cycle was completed. In order to determine colonization dynamics each sample was observed under optical and confocal microscope after staining. Gametophyte was classified as Adiantum type. Male and female gametangia were limited to the lower face, mycorrhizal colonization started when they were differentiated and took place through the rhizoids. Spores and vesicles were not found in this cycle stage. Paris-type mycorrhizal colonization was established in the midrib and in the embrionary foot. It was colonized by external mycelium. When the first root was developed soil inoculum colonized de novo this structure and Arum-type colonization was observed. This study proves that the type of colonization is determined by the structure of the host, not by the fungus. Both the gametophyte and embryo foot have determined growth and Paris-type colonization, while, sporophyte roots have undetermined growth and Arum-type colonization. The structures found in vitro cultures were highly similar to those found under natural conditions. Rev. Biol. Trop. 60 (2): 857-865. Epub 2012 June 01.

Los helechos presentan dos etapas en su ciclo de vida, una fase esporofítica y una gametofítica. Estos por lo general pueden colonizar diferentes ambientes y frecuentemente presentan raíces micorrizadas. Este estudio describe la asociación experimental entre Pteris vittata, un helecho leptosporangiado y una cepa de Glomus intraradices durante el ciclo de vida del helecho, desde la germinación de las esporas hasta el desarrollo del esporofito maduro. El objetivo de este estudio fue comparar los patrones de colonización de G. intraradices a lo largo de todo el ciclo de vida del helecho con los tipos encontrados en la naturaleza. Las esporas maduras fueron obtenidas de frondes fértiles de P. vittata que crecen sobre las paredes de la ciudad de Buenos Aires, Argentina. Las raíces se tiñeron y fueron observadas bajo microscopio óptico para el estudio de la colonización micorrízica. Aproximadamente 75 esporas de helecho se cultivaron en macetas con un sustrato estéril y con un inóculo de G. intraradices (N° 51.331 BAFC) en la superficie. Después de la germinación, se tomaron muestras cada 15 días hasta que se completó el ciclo de vida del helecho. Con el fin de determinar la dinámica de la colonización, cada muestra se observó con el microscopio óptico y el microscopio de confocal luego de la tinción correspondiente. El gametofito fue clasificado como del tipo “Adiantum”. Los gametangios femeninos y masculinos se desarrollaron en la cara inferior del mismo. La micorrización comenzó cuando los gametangios estaban ya diferenciados y la colonización se produjo a través de los rizoides. Las esporas y las vesículas no se encontraron en esta fase del ciclo. La micorrizacion tipo Paris se observó sobre la línea de la nervadura central. El pie del esporofito fue colonizado por el micelio externo. Cuando la raíz se desarrolló, se colonizó “de novo”, y se observó una colonización de tipo Arum. Este estudio demuestra que el tipo de colonización está determinado por la estructura del helecho y no por el hongo. Tanto el gametofito como el pie del embrión tienen crecimiento definido y colonización tipo Paris, mientras que las raíces del esporofito presentan un crecimiento indeterminado y una colonización tipo Arum. Las estructuras que se encontraron bajo cultivo coinciden con las que se encontraron en condiciones naturales.

Spore germination and gametophyte development of Cyathea atrovirens (Langsd. & Fisch.) Domin (Cyatheaceae) under different pH conditions

Cyathea atrovirens (Langsd. & Fisch.) Domin, an intensely exploited tree fern, is found inside forests in several succession stages, as well as in swamps, roadsides and unused fields in the Rio dos Sinos basin, in the state of Rio Grande do Sul, southern Brazil. This study evaluated the in vitro germination and gametophyte development of C.atrovirens under different pH conditions, as well as spore viability after different storage times at 7 ºC. The lowest germination rate of spores was obtained at pH 7.0. At pH 5.0 to 6.5, laminar gametophyte development started at 20 to 30 days of culture. Antheridia and archegonia were first observed at 35 and 128 days, respectively. Storage at 7 ºC did not affect germination rates. The capability of germination at different pH levels may explain the occurrence of the species in a wide range of habitats. The present study contributes to the understanding of the full life-cycle of C. atrovirens and to the analysis of the influence of abiotic components, providing information for the cultivation, management and conservation of the species.

Cyathea atrovirens (Langsd. & Fisch.) Domin, uma samambaia arborescente alvo de exploração extrativista, é encontrada no interior de florestas em diferentes estádios de sucessão, banhados, margens de estradas e campos abandonados da bacia do rio dos Sinos, no Estado do Rio Grande do Sul, sul do Brasil. Este estudo avaliou a germinação e o desenvolvimento gametofítico in vitro de C. atrovirens sob diferentes condições de pH, bem como a viabilidade de esporos após diferentes períodos de armazenamento a 7 ºC. A menor taxa de germinação de esporos foi obtida no pH 7,0. Entre os pHs 5,0 e 6,5, o início de desenvolvimento laminar dos gametófitos ocorreu entre 20 e 30 dias de cultura. Anterídios e arquegônios foram observados a partir do 35º e do 128º dia, respectivamente. A estocagem a 7ºC não afetou as taxas de germinação. A capacidade de germinação em diferentes pHs pode explicar a ocorrência da espécie em um amplo espectro de hábitats. O presente estudo contribui para a compreensão do ciclo de vida completo de C. atrovirens e para a análise da influência de fatores abióticos, fornecendo subsídios para o cultivo, o manejo e a conservação da espécie.

Gametófitos y esporófitos jóvenes de cuatro especies de helechos del género Pteris (Pteridaceae) naturalizadas en América

Gametophytes and young sporophytes of four species of the fern genus Pteris (Pteridaceae) naturalized in the American continent. The pantropical fern genus Pteris L. has about 250 species of which 60 occur in the American continent. We studied the morphogenesis of the gametophyte, and the morphology of the young sporophytes of four species: P. cretica, P. ensiformis, P. multifida and P.vittata, together with a palynological analysis that includes the ability of spores to germinate. Gametophytes were obtained trough in vitro culture techniques with agar-gellified Knudson medium. Young sporophytes were placed in earth-sand (3:1) sterile substrate. We used light and SEM microscopy. Triletes spores predominate, but monolete, tetralete, and other types of apertura are often found. The viability of spores is not affected by the variation, so the term spore polymorphism is applied to the condition occurring among these species. Spore polymorphism is similar in P. cretica and P. multifida. Germination occurs following the Vittaria type, 3-7 days after the sowing. Filamentous, 3-5 celled gametophytes were found in P. cretica, P. multifida and P. vittata, and 7-9 celled in P. ensiformis. Development of gametophytes takes place following Adiantum type and eratopteris type. The symmetry of the laminae differ in gametophytes, those of P. ensiformis and P. multifida are similar and differ from the other two species, P. cretica and P. vittata. Gametophytes of P. ensiformis, P. multifida and P. vittata are bisexual and protandric, while male gametophytes were found in P. cretica. Antheridia correspond to the common leptosporangiate type; they are cylindric in P. vittata and ovoid in the other three species. Archegonia necks have 4 rows of 4 cells each. The sporophytes complete their development 3 months after sowing, and have indument close to the adult plants. P. cretica shows obligated apogamy. Rev. Biol. Trop. 58 (1): 89-102. Epub 2010 March 01.

El género pantropical Pteris L. tiene 250 especies de la cuales 60 están en el continente Americano. Se estudió la morfogénesis de los gametófitos, y la morfología de los esporófitos jóvenes de cuatro especies: P. cretica, P. ensiformis, P. multifida y P.vittata, junto con un análisis palinológico que incluye la capacidad de las esporas de germinar. Los gametófitos se obtuvieron mediante técnicas de cultivo in vitro. Los esporófitos jóvenes se trasladaron a sustrato estéril de tierra y arena (3:1). Se usó el microscopio de luz y el de barrido (SEM). Se encontraron esporas con diferentes tipos de aperturas. La germinación ocurre entre 3-7 días y corresponde al tipo Vittaria. Se encontraron gametófitos filamentosos formados por 3-5 células en P. cretica, P. multifida y P. vittata y por 7-9 células en P. ensiformis. El desarrollo gametofítico ocurre de dos formas: tipo Adiantum y tipo Ceratopteris. Los gametófitos de P. ensiformis, P. multifida y P. vittata son monoicos y protándricos. P. cretica desarrolla gametófitos anteridiados. Los anteridios corresponden al tipo común de los helechos leptosporangiados, son cilíndricos en P. vittata y ovoides en las otras tres especies. Los cuellos de los arquegonios tienen 4 hileras con 4 células cada una. Los esporófitos se desarrollan después de los 3 meses de su siembra y su indumento es semejante a las plantas adultas. P. cretica presenta apogamia obligada.

Sporophyte morphology and gametophyte development of the fern Blechnum sprucei (Pteridophyta: Blechnaceae)

The fern Blechnum sprucei grows in Mesoamerica (Costa Rica) and South America, from Colombia to Bolivia, SE and centre of Brazil, Paraguay and Argentina. It is a distinctive, somewhat vulnerable, mostly orophilous species. Fresh and dry herbarium material was used for this study. Herbarium material for anatomical studies comes from CTES, BA, LP, MA, SI and UC (Holmgren et al.1990). Selected representative specimens are additionally cited after taxonomic treatment of the species. Dry material was restored with aqueous 4:1 butil cellosolve. Pinnae were cleared with aqueous 6% NaOH, then coloured with aqueous 1 % TBO (Gurr 1966). Hand made transverse sections of young and adult stipes, and costae were done in fresh and restored herbarium material. Venation and epidermal patterns were analyzed in basal, apical and medium pinnae, but only the latter were illustrated. The size and density of stomata were measured in medium pinnae from all studied samples, values shown are the average of 25 measures per sample; sizes are expressed as minimum, media and maximum length x width, in µm, and density as minimum, media and maximum number of stomata / mm². Spores were studied with SEM, mounted on metal stubs with double sided tape, covered with gold under vacuum and photographed with a Jeol /EO JSM 6360 (15 KV) SEM. Spores were also studied with light microscope, mounted in DePex (DePex mounting medium, Gurr, BDH Laboratory Supplies, Poole BH15 1TD, UK) and measured using an ocular micrometer. Measurements are based on a minimum sample of 100 spores taken from different specimens. Sizes are expressed as the longest equatorial diameter/ polar diameter, in µm. Gametophytes were studied from material collected in the subtropical forest of Tucumán Province, Argentina. Spore samples for cultures were taken from single sporophytes kept dry at room temperature since the date plants were collected. Gametophytes were grown under fluorescent light. Multispore cultures were established on mineral agar. Percentage of germination was recorded for a random sample of 50 spores from each of the two plates, every three days until there was no further increasing. Gametophytes were stained with chloral hydrate acetocarmine. The species has large sporophytes, suberect, scaly rhizomes, and dimorphic fronds with short, scaly stipes and lanceolate to elliptic sterile laminae. The rachises can grow indefinitely as radicant axis that vegetatively multi-plicate the plants. Pinnae are lanceolate, herbaceous, with crenate and papillose margins, superficially scaly and hairy, peciolulate, with free, visible veins regularly once furcated near the costa, ending in large, active hydathodes. The broadly elliptic fertile laminae bear distant pinnae, with vegetative tissue reduced to the portion that supports the indusium and the continuous coenosorus; terminal indefinite rachis, not proliferous, may be present. Rev. Biol. Trop. 56 (4): 2027-2040. Epub 2008 December 12.

El helecho Blechnum sprucei crece en Mesoamérica (Costa Rica) y Sudamérica, desde Colombia a Bolivia, SE y centro de Brasil, Paraguay y Argentina. Es una especie característica, algo vulnerable y orófila. Se estudiaron caracteres exomorfológicos de especimenes provenientes de distintos puntos de su gran área de distribución. Adicionalmente, se llevó a cabo un detallado análisis de los modelos epidérmicos jóvenes y maduros, del indumento de la lámina y los ejes, y de la organización vascular en los estipes y costas. Se han estudiado por primera vez la morfología esporal, el desarrollo de los gametófitos, que resultaron cordados y pelosos, y su expresión sexual. Presenta esporófitos grandes, suberectos, con rizomas escamosos y frondas dimórficas, con estipes cortos y escamosos y láminas estériles de lanceoladas a elípticas. El raquis puede crecer indefinidamente como un eje radicante que multiplica las plantas vegetativamente. Las pinnas son lanceoladas, herbáceas, con márgenes crenados y papilosos, y la superficie escamosa y pelosa. Son pecioluladas, con venas libres y visibles, regularmente furcadas cerca de la costa, terminando en hidatodos grandes y activos. Las láminas fértiles son anchamente elípticas y portan pinnas distales; presentan tejido vegetativo reducido a la porción que soporta el indusio y el cenosoro continuo. Pueden presentar raquis indefinidos, pero no prolíferos.

Mycorrhizal-like interaction between gametophytes and young sporophytes of the fern Dryopteris muenchii (Filicales) and its fungal endophyte

The morphology of a Glomus-like fungus-host interaction in chlorophyllous gametophytes and young apogamic sporophytes of Dryopteris muenchii A.R. Sm. was studied from ferns cultivated in laboratory, using soil as substrate. An aseptate fungus colonized the gametophytes’ tissue through the rhizoids, developing vesicles. The fungus penetrated the young sporophytes primary roots by developing appressoria. It spread forming inter- and intra-cellular hyphae through the epidermis and the outermost cortical cell layers, where it formed vesicles, hyphal coils-like and arbuscules. The fungus hyphae never colonized the gametophyte-sporophyte cellular junction. The fungal structures observed on D. muenchii during this study, are rather similar to those reported for the plant host-arbuscular mycorrhizal fungus (AMF) interaction, where the AMF described belonged to Phylum Glomeromycota. Therefore, this study is a contribution to the scarce knowledgement of the association between AMF and chlorophyllous gametophytes and young apogamic sporophytes of ferns. Rev. Biol. Trop. 56 (3): 1101-1107. Epub 2008 September 30.

Se describe la morfología de un hongo endófito afín al género Glomus, como colonizador de gametofitos clorofílicos y de esporofitos apogámicos jóvenes del helecho Dryopteris muenchii A.R. Sm.; el estudio se llevó a cabo con helechos cultivados en el laboratorio y utilizando tierra como substrato. El tejido del gametofito fue colonizado, a través de los rizoides, por un hongo miceliar aseptado, el cual formó vesículas. El hongo logró penetrar las raíces primarias de los esporofitos jóvenes desarrollando apresorios. El hongo se dispersó formando hifas inter- e intra-celulares a través de la epidermis y de la capa de células corticales más externas, donde produjo vesículas, estructuras similares a ovillos y arbúsculos. Las hifas del hongo nunca colonizaron las células de la unión entre el gametofito y el esporofito. Las estructuras observadas durante este estudio en D. muenchii, son muy similares a las de la interacción planta hospedera-hongo micorrícico arbuscular (HMA), en donde el HMA descrito corresponde al Phylum Glomeromycota. Por lo anterior, este estudio es una contribución al escaso conocimiento que se tiene sobre la asociación entre los HMA y gametofitos clorofílicos y esporofitos apogámicos de helechos jóvenes.