Hongos micorrízicos en Vanilla spp. (Orchidaceae) y su potencial para la germinación de semillas

Abstract

Las orquídeas dependen completamente de los hongos micorrízicos para la germinación de sus semillas. A pesar que esta interacción es ecológicamente importante para comprender la biología de las orquídeas, se conoce muy poco de ella en las zonas tropicales. Vanilla es un género de orquídeas tropical especialmente interesante por incluir especies de importancia económica, pues a partir de éstas se extrae la vanilina; un saborizante y aromatizante de gran consumo a nivel mundial. El objetivo de este estudio fue investigar la diversidad de hongos asociados a tres especies de Vanilla nativas del Valle del Cauca, que exhiben características interesantes para el desarrollo de propuestas productivas, y comprobar su función micorrízica en procesos de germinación simbiótica. Para lograr esto, se colectaron las raíces de las plantas y se identificaron sus hongos micorrízicos a partir de secuencias nucleotídicas de la región de los espaciadores internos transcritos de los genes nucleares ribosomales (nrITS). Estas secuencias fueron obtenidas tanto de cultivos puros, como de amplificación directa a partir de tejidos con pelotones. Se obtuvo un total de 20 secuencias (10 por el método de amplificación directa y 10 por el método de cultivo) que correspondieron a ocho OTUs; cinco de las cuales son nuevas accesiones para la base de datos del Gen-Bank. Las especies V. odorata y V. calyculata, se relacionaron con hongos de los géneros Tulasnella y Ceratobasidium. Mientras que en la especie V. rivasii sólo se logró determinar hongos asociados al género Tulasnella. El análisis filogenético mostró que las secuencias obtenidas de Tulasnella se agruparon en dos clados distantes. Se realizó la caracterización morfológica de los 10 aislamientos obtenidos y se comprobó que la variación presentada en los caracteres evaluados en las Tulasnella no permite una caracterización clara para este grupo. Mientras que los aislados de Ceratobasidium se ajustan más a las descripciones para el género-forma Rhizoctonia. En la evaluación del proceso de germinación, los aislados de Ceratobasidium tuvieron mayor potencial que los de Tulasnella. No se presentó especificidad entre la especie fuente de los aislados, y la especie en la que se probó la germinación de las semillas. De las tres especies de Vanilla de estudio, sólo V. calyculata y V. rivasii presentaron germinación; siendo esta última en la que el proceso se presentó con mayor éxito en relación a los porcentajes de germinación e índice germinativo. Se logró determinar y esquematizar las diferencias en la morfología de los protocormos en cada etapa de germinación en las especies en las que se presentó dicho proceso. Este estudio representa una gran contribución al conocimiento de la biología de la simbiosis para las especies de Vanilla de estudio, así como para futuras investigaciones donde la reproducción por semilla es importante, como en la búsqueda de híbridos con rasgos deseables en relación a sus características organolépticas, resistencia a plagas y enfermedades. De la misma manera, estos métodos in vitro pueden emplearse como estrategias de conservación con el fin de promover la variabilidad genética de este recurso fitogenético considerado amenazado y sub-utilizado. / Abstract. Abstract starts here Orchids depend entirely on mycorrhizal fungi for seed germination. Although this interaction is ecologically important to understand the biology of orchids, very little of it is known in the tropics. Vanilla is a genus of tropical orchids especially interesting to include economically important species, because from these extracted vanillin; a flavoring and flavoring in great demand worldwide demand. The aim of this study was to investigate the diversity of fungi associated with three species of native Vanilla from Valle del Cauca (Colombia), which exhibit interesting development proposals productive characteristics and check its function in mycorrhizal symbiotic germination processes. To accomplish this, cultured and uncultured mycorrhizal fungi were identified by sequencing the internal transcribed spacer region of nucelar rDNA (nrITS). A total of 20 sequences (10 corresponded to direct amplification method, and 10 the culture method) which correspond to eight OTUs, five of which are new accessions in the database GenBank. The species V. odorata and V. calyculata, were associated with fungi of the genera Ceratobasidium and Tulasnella. While in the species V. rivasii only was achieved determine Tulasnella associated fungi. Phylogenetic analysis showed that the sequences obtained from Tulasnella formed two distant clades. Morphological characterization of the 10 isolates were performed and i found that the variation in the traits presented in Tulasnella not allow a clear characterization for this group. While Ceratobasidium isolates were more fit the descriptions for the form-genus Rhizoctonia . In the evaluation of the germination process, Ceratobasidium isolates had greater potential than the Tulasnella. No relation of specificity provided between the source of the isolated species, and the species in which seed germination was tested. Of the three species of Vanilla , only V. calyculata and V. rivasii showed germination. In V. rivasii the process occurred more success in relation to germination and germination index. It was possible to identify and outline the differences in the morphology of protocorms in each stage of germination in species in which this process was presented. This study represents a major contribution to knowledge of the biology of symbiosis Vanilla species and for future research where reproduction by seed is important, such as in the search for hybrids with desirable traits in relation to their organoleptic characteristics, resistance to pests and diseases. Likewise, these in vitro methods can be used as conservation strategies to promote this genetic variability considered threatened plant genetic resource

//Abstract: Orchids depend entirely on mycorrhizal fungi for seed germination. Although this interaction is ecologically important to understand the biology of orchids, very little of it is known in the tropics. Vanilla is a genus of tropical orchids especially interesting to include economically important species, because from these extracted vanillin; a flavoring and flavoring in great demand worldwide demand. The aim of this study was to investigate the diversity of fungi associated with three species of native Vanilla from Valle del Cauca (Colombia), which exhibit interesting development proposals productive characteristics and check its function in mycorrhizal symbiotic germination processes. To accomplish this, cultured and uncultured mycorrhizal fungi were identified by sequencing the internal transcribed spacer region of nucelar rDNA (nrITS). A total of 20 sequences (10 corresponded to direct amplification method, and 10 the culture method) which correspond to eight OTUs, five of which are new accessions in the database GenBank. The species V. odorata and V. calyculata, were associated with fungi of the genera Ceratobasidium and Tulasnella. While in the species V. rivasii only was achieved determine Tulasnella associated fungi. Phylogenetic analysis showed that the sequences obtained from Tulasnella formed two distant clades. Morphological characterization of the 10 isolates were performed and I found that the variation in the traits presented in Tulasnella not allow a clear characterization for this group. While Ceratobasidium isolates were more fit the descriptions for the form-genus Rhizoctonia. In the evaluation of the germination process, Ceratobasidium isolates had greater potential than the Tulasnella. No relation of specificity provided between the source of the isolated species, and the species in which seed germination was tested. Of the three species of Vanilla , only V. calyculata and V. rivasii showed germination. In V. rivasii the process occurred more success in relation to germination and germination index. It was possible to identify and outline the differences in the morphology of protocorms in each stage of germination in species in which this process was presented. This study represents a major contribution to knowledge of the biology of symbiosis Vanilla species and for future research where reproduction by seed is important, such as in the search for hybrids with desirable traits in relation to their organoleptic characteristics, resistance to pests and diseases. Likewise, these in vitro methods can be used as conservation strategies to promote this genetic variability considered threatened plant genetic resource.