M. Castaño

Emergence and partial characterization of rice stripe necrosis virus and its fungus vector in South America

A new disease of rice, known as ‘entorchamiento’ (crinkling), was first noticed in the Department of Meta, Colombia, in 1991. Symptoms include seedling death, foliar striping and severe plant malformation. Tissue extracts and purified preparations from diseased rice plants, contained virus-like particles ca. 20 nm in diameter, with a bimodal length of 260 and 360 nm. Particle aggregates were also observed in the cytoplasm of infected rice leaf cells. Electrophoretic analyses of purified preparations and dsRNA extracts, revealed a single protein species of M 22,500, and four dsRNA bands ca. 6300, 4600, 2700 and 1800 bp in size. Cystosori, characteristic of plasmodiophorid fungal vectors of plant viruses, were consistently observed in the roots of diseased rice plants. PCR and sequence analyses of amplified fungal DNA products from infected rice roots, revealed that the putative fungus vector was Polymyxa graminis. A Western blot of tissue extracts obtained from ‘crinkled’ rice plants from Colombia, using antiserum against a West African isolate of rice stripe necrosis furovirus (RSNV), resulted in the detection of a protein band of approximately M 22,000. The RSNV antiserum recognized the Colombian virus isolate in serologically specific electron microscopy tests. These results confirm the presence of RSNV in the Americas.

Natural infection of tropical forage legume species of Arachis and Stylosanthes by potyviruses related to peanut mottle virus

The South American forage legume Arachis pintoi was found to be affected by foliar ring spot symptoms in surveys of various localities in the Cauca Valley of Colombia. A filamentous virus (approximately 750 nm) isolated from symptomatic A. pintoi plants induced the characteristic ring spot symptoms in manually inoculated virus-free A. pintoi plants. This virus also caused systemic infection of other legumes, such as common bean, cowpea,peanut, and soybean, in manual transmission tests

A sibemovirus hindering the utilization of Calopogonium mucunoides as a forage legume in the lowland tropics

The cultivation of calopo, Calopogonium mucunoides, as a promising forage legume for the lowland tropics, was hindered by its susceptibility to a severe yellow mosaic disease observed in the Eastern Plains of Colombia. An isometric virus ca. 28 nm in diameter was observed by electron microscopy in leaf extracts and purified preparations, and in phloem cells of systemically infected calopo plants. The virus was transmitted by mechanical means and by the chrysomelid beetle Diabrotica balteata. The host range of the virus was restricted to the legumes Phaseolus vulgaris, Vigna unguiculata, V. radiata, Centrosema spp., and Senna occidentalis. The physical and chemical properties of the calopo virus were similar to those reported for the sobemovirus group, and the virus was antigenically related to the bean and cowpea strains of southern bean mosaic virus (SBMV). However, the host range of the calopo virus differed from the pathogenicity spectra of the bean, cowpea, Ghanaian, and Mexican strains of SBMV. Nucleotide sequence analysis of a 609 bp fragment amplified from the coat protein region of the calopo sobemovirus revealed similarities of 81.8 and 66.1% with the corresponding regions of the bean and cowpea strains, respectively, of SBMV. The respective homologies increased to 83.7 and 67.8% when the deduced amino acid sequences of these viruses were compared. It is concluded that the mosaic disease of calopo is caused by a previously undescribed sobemovirus for which the name calopo yellow mosaic virus is suggested.

Detection of a strain of soybean mosaic virus affecting tropical forage species of Centrosema

A filamentous virus about 715 nm long was isolated from a plant of the tropical forage legume Centrosema macrocarpum affected by mosaic. Ultrathin sections of symptomatic leaf tissue showed pinwheel inclusions in the cytoplasm of infected cells.(.)Purified virus preparations had an absorbance ratio (A 260/280) of 1.13, contained a single protein of relative molecular weight 32,500 and had a 9-kb nucleic acid species(.)

DETECCIÓN DEL VIRUS DEL MOSAICO DE LA ALFALFA EN REGIONES PRODUCTORAS DE FREJOL (Phaseolus vulgaris L.) EN CHILE

En los ultimos anos se han observado plantas de frejol (Phaseolus vulgaris) con sintomas caracteristicos de una enfermedad viral. Durante las temporadas 1993/1994 y 1995/1996 se realizaron prospecciones de campos de frejol en la zona productora (V a la VIII Region) de Chile. Se colectaron un total de 173 muestras de plantas afectadas por diferentes sintomas de posible etiologia viral. Las plantas fueron sometidas a la prueba de ELISA con un antisuero para el Virus del Mosaico de la Alfalfa (AMV). Se determino que era el AMV, el cual estaba distribuido en el area productora de frejol de Chile, pero con una frecuencia de deteccion relativamente baja, del 2 y 4% respectivamente, para las temporadas mencionadas. El procedimiento descrito junto con la utilizacion de antisuero es el metodo adecuado y propuesto para la deteccion de AMV.

Detection of a potyvirus related to guineagrass mosaic virus infecting Brachiaria spp. in South America

A filamentous virus approximately 775 nm long was isolated from variegated plants of the tropical forage grass Brachiaria spp. collected in Colombia and Brazil, South America. Ultrathin sections of symptomatic leaf tissue showed cylindrical inclusions (scrolls) in the cytoplasm of infected cells. The virus was transmitted mechanically to selected species of Brachiaria, Panicum, and Paspalum but not to maize, sorghum, or sugarcane. The virus was also transmitted from and to B. brizantha by the aphid Myzus persicae in a nonpersistent manner. The virus was not seedborne in Brachiaria spp