Colletotrichum gloeosporioides, pathogen of orchids in the northeast of Argentina

4 ilus. 10 ref.El objetivo de este trabajo fue identificar el agente causal de manchas foliares detectadas en plantas Orchidaceae del noreste (NE) de Argentina. Desde el 2001, se recolectaron muestras con s?ntomas de enfermedad en invernaderos de las ciudades de Corrientes, Resistencia (Chaco) y Formosa, y muestras procedentes de Esteros de Iber? (Corrientes). Los cultivos sobre agar-papa-glucosa produjeron abundantes colonias de micelio a?reo gris y conidios unicelulares, oblongos, hialinos, con extremos redondeados de 16,0 a 24,0 ?m x 4,0 a 6,0 ?m. Las setas fueron rectas y oscuras. Sobre la base de caracter?sticas morfol?gicas, el hongo se identific? como Colletotrichum gloeosporioides Penz. Sacc. Se manifest? el teleomorfo Glomerella cingulata. Se determin? la patogenicidad de un aislamiento sobre hojas de Cattleya intermedia x C. walkeriana, Dendrobium nobile Lind. y Miltonia flavescens Lind. en inoculaciones con heridas, y se observaron s?ntomas una semana despu?s de la inoculaci?n. Se reaisl? a C. gloeosporioides como pat?geno. Este es el primer informe de C. gloeosporioides afectando diversas especies de orqu?deas en el NE de Argentina. The aim of this study was to identify the causal agent of leaf spots detected in Orchidaceae plants from the Argentinian northeast (NE). Since 2001, samples with symptoms were collected in greenhouses from the cities of Corrientes, Resistencia (Chaco) and Formosa, and from Esteros del Iber? (Corrientes). Cultures on potato-glucose-agar yielded abundant, gray aerial mycelium and unicellular, hyaline, oblong conidia, with rounded ends. Conidial size ranged from 16.0 to 24.0 ?m x 4.0 to 6.0 ?m. Setae were straight and dark. Based on morphological characteristics, the fungus was identified as Colletotrichum gloeosporioides Penz. Sacc. The teleomorph Glomerella cingulata was developed. Pathogenicity of the fungus was determined on leaves of Cattleya intermedia x C. walkeriana, Dendrobium nobile Lind. and Miltonia flavescens Lind. Seven days after inoculation, symptoms appeared that were similar to those originally observed on the orchid leaves. C. gloeosporioides was isolated again from infected leaves, confirming it as the pathogen. The fungus was reported as a pathogen on 19 genera and species of orchids. This is the first report of C. gloeosporioides as a pathogen of several orchid species in the Argentinian NE

Cryopreservation of seeds and in vitro-cultured protocorms of Oncidium bifolium Sims. (Orchidaceae) by encapsulation-dehydration

Encapsulation-dehydration was employed for cryopreserving seeds and in vitro-cultured protocorms of Oncidium bifolium. Freshly harvested seeds, 120 days after pollination, were encapsulated in beads containing 1/2 MS medium with 3% sucrose and 3% calcium alginate and subsequently pretreated in agitated (80 rpm) liquid medium supplemented with 0.15 M sucrose (24 h) followed by 0.25 M sucrose (48 h), 0.5 M sucrose (24 h) and 0.75 M sucrose (24 h). The beads with seeds were dehydrated with silica gel for 5 h to 19.2% moisture content and immersed in liquid nitrogen for I h, thawed at 30 degrees C for 2 min, post-treated using the same series of liquid media [0.5 M sucrose (24 h), 0.25 M sucrose (48 h), 0.15 M sucrose (24 h)], and recultured on 1/2 MS medium with 0.1 M sucrose and 0.7% agar. As much as 4.8% of the cryopreserved seeds produced complete plants. In-vitro cultured protocorms were successfully cryopreserved following the same procedure, allowing 11.3% of them to produce plants