Effects of Exogenous Auxins on Tomato Tissue Infected With the Citrus Exocortis Viroid

Leaf disks, stem segments, and callus cultures from healthy and CEVinfected plants of a hybrid of Lycopersicon esculentum and Lycopersicon peruvianum were cultured in vitro under different hormone regimes. The differences in response observed when the medium was supplemented with auxins, alone or in combination with cytokinins, suggest that the inability of CEV-infected cells to respond to auxins might be involved in the development of the pathogenic syndrome caused by CEV

Influencia de virus y similares en el desarrollo de yemas de cítricos cultivadas “in vitro”

Se estudio el efecto de seis agentes patógenos en el desarrollo de yemas de citricos cultivadas in vitro y la obtención de plantas a partir de las mismas. Las enfermedades estudiadas fueron la tristeza causada por un closterovirus (CTV), el infectious variegation causado por un virus ilar (CIVV), el vein enation y la psoriasis que son enfermedades de etiologia desconocida transmisibles por injerto, y la exocortis y la cachexia producidos por un complejo de viroides

Identification and Characterization of a Variant of Citrus viroid V (CVd-V) in Seminole Tangelo

Previous studies on Atalantia citroides, a citrus relative that appeared to be immune to viroid infection, revealed the existence of a new viroid, which was designated tentatively as Citrus viroid-V (CVd-V) and has been proposed as a new member of the genus Apscaviroid within the family Pospiviroidae. Biological indexing of a Seminole tangelo tree on the Etrog citron indicator followed by sPAGE analysis revealed the presence of a viroid that has been characterized as a new variant of CVd-V. The variant has 97.6% sequence identity with the reference sequence of CVd-V and shows three characteristics: (I) two compensatory changes that modify an A-U base pair between the upper and lower “strands” into a G-C base pair, (II) a U→A change located in a loop that does not seem to disturb the viroid secondary structure, and (III) two sets of changes located in the upper and lower strands that result in a rearrangement of the base pairing between the upper and lower strands. Infectivity studies performed with an artificial mutant revealed the existence of structural constraints in the region in which major differences between CVd-V and the Seminole tangelo variant were identified

Changes in the Pathway of Ethylene Production Following Citrus Exocortis Viroid Infection in Tomato Plants

Ethylene production was stimulated during the systemic reaction of Rutgers tomato to citrus exocortis viroid (CEV) infection. The increase in ethylene production of CEV-infected leaf discs was parallel to the increase in 1-aminocyclopropane-1-carboxylic acid (ACC) production, and content. Moreover, the capacity to convert ACC into ethylene (ethylene forming enzyme activity) in CEV-infected leaves also increased. The blockage of ACC synthase with aminooxyacetic acid (AOA) completely prevented the viroid-induced production of ethylene, thus indicating that this enzyme is the primary controlling step of ethylene biosynthesis acted upon in viroid infection. The increased ethylene-forming enzyme (EFE) activity acts as a secondary contributor to the enhanced production of ethylene

Two nucleotide positions in the Citrus exocortis viroid RNA associated with symptom expression in Etrog citron but not in experimental herbaceous hosts

P>Citrus exocortis viroid (CEVd) is the causal agent of exocortis disease of citrus. CEVd has a wide host range that includes woody and herbaceous species. A new CEVd strain (CEVdCOL), phylogenetically clustering with CEVd variants of Class A inducing severe symptoms in tomato, was identified in Colombia and shown to induce only extremely mild symptoms in Etrog citron indicator plants. Using site-directed mutagenesis, two nucleotide substitutions (314A -> G and 315U -> A) in the lower strand of the P domain of the predicted CEVdCOL secondary structure resulted in a severe artificial CEVdMCOL variant. Conversely, two nucleotide exchanges (314G -> A and 315A -> U) in the same region of the severe variant CEVdE-117 resulted in a symptomless artificial CEVdME-117 variant. Infectivity assays conducted with the natural and mutated variants showed that all induced severe symptoms in Gynura aurantiaca, tomato and chrysanthemum. This is the first report of the identification of pathogenic determinants of CEVd in citrus, and shows that these pathogenicity determinants are host dependent

Morfogénesis de cultivos de tejidos de cítricos infectados con virus y similares

Se llevó a cabo un estudio con el fin de determinar el efecto de cinco agentes patógenos en la morfogénesis de cultivos de tejidos de cítricos. Entrenudos de controles sin inocular y de plantas infectadas fueron cultivados i n vitro. Las enfermedades estudiadas fueron la tristeza, causada por un closterovirus (CTV), la infección variegada causada por un virus ilar (CIVV), la cachexia causada por un viroide (CCaV), y el vein enation y la psoriasis que son enfermedades de etiología desconocida transmisibles por injerto. En todos los casos se observó una reducción de la rizogénesis en los tejidos infectados. También se observaron diferencias en la regeneración de yemas y brotes adventicios. Se observó una disminución de la regeneración en la mayoría de combinaciones patógeno/hospedador estudiadas. Sin embargo algunos hospedadores tolerantes se comportaron como los controles, y los cultivos de naranjo con un aislado débil de psoriasis mostraron un incremento en el número de brotes y yemas regeneradas. Los cambios morfogénicos dependían del patógeno, el aislado y el hospedador empleado