Identification and characterization of citrus concave gum-associated virus infecting citrus and apple trees by serological, molecular and high-throughput sequencing approaches

Citrus concave gum-associated virus (CCGaV) is a negative-stranded RNA virus, first reported a few years ago in citrus trees from Italy. It has been reported in apple trees in the USA and in Brazil, suggesting a wider host range and geographic distribution. Here, an anti-CCGaV polyclonal antiserum to specifically detect the virus has been developed and used in a standard double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) that has been validated as a sensitive and reliable method to detect this virus both in citrus and apple trees. In contrast, when the same antiserum was used in direct tissue-blot immunoassay, CCGaV was efficiently detected in citrus but not in apple. Using this antiserum, the first apple trees infected by CCGaV were identified in Italy and the presence of CCGaV in several apple cultivars in southern Italy was confirmed by field surveys. High-throughput sequencing (HTS) allowed for the assembling of the complete genome of one CCGaV Italian apple isolate (CE-c3). Phylogenetic analysis of Italian CCGaV isolates from apple and citrus and those available in the database showed close relationships between the isolates from the same genus (Citrus or Malus), regardless their geographical origin. This finding was further confirmed by the identification of amino acid signatures specific of isolates infecting citrus or apple hosts. Analysis of HTS reads also revealed that the CE-c3 Italian apple tree, besides CCGaV, was simultaneously infected by several viruses and one viroid, including apple rubbery wood virus 2 which is reported for the first time in Italy. The complete or almost complete genomic sequences of the coinfecting agents were determined

Identification, full-length genome sequencing, and field survey of citrus vein enation virus in Italy

Citrus vein enation virus (CVEV) was described in Spain and then it has been reported in several citrus growing areas of Asia, America and Australia. Here, the occurrence of CVEV in Italy has been documented for the first time. The full genome sequence of a CVEV Italian isolate (14Q) was determined by high-throughput sequencing and the presence of the virus was confirmed by RT-PCR and graft-transmission to indicator plants, from which the virus was recovered six-months post-inoculation. Phylogenetic analysis based on the full-length genome of CVEV isolates from different countries showed that they are phylogenetically related to each other based on their geographic origin, rather than on their host and that the Italian isolate is more closely related to the Spanish isolate than to the other ones. A field survey revealed the presence of CVEV in some areas of Campania region (southern Italy), prevalently infecting lemon trees. In the frame of this survey, kumquat was identified for the first time as a host of CVEV. No symptoms were observed in the field so far. The infection of asymptomatic hosts and the transmission by aphid species present in Italy increase the risk that the virus could further spread

Performance evaluation of the low-voltage CML D-latch topology

Abstract In this paper, the low-voltage CML D-latch topology is analyzed and compared to the traditional implementation to evaluate its speed potential and power efficiency, which are crucial aspects in current applications. To this end, an analytical delay model is first derived and then used to optimize its speed performance and understand its power-delay interdependence. The delay model, based on the approach proposed by Alioto and Palumbo (IEEE Trans. Circuits Systems I 46(11) (1999) 1330; IEEE Trans. Circuits and Systems II 47(5) (2000) 452), leads to simple expressions that are suitable for pencil-and-paper evaluations. The accuracy of the expressions obtained is tested by comparison to SPICE simulations, by using a bipolar process whose npn transistor has a transition frequency of 20 GHz. The delay expressions derived are used to design and compare the low-voltage and the traditional D-latch both in terms of delay and power-delay tradeoff, by considering a high-performance and a low-power consumption design target. The analytical comparison carried out is general, since it does not depend on the specific bipolar process considered. Analysis shows that the low-voltage D-latch topology does not necessarily allow for a power saving or a better power efficiency, and applications where this topology exhibits some advantage over the traditional implementation are identified.

Errores en la adquisición de lenguas extranjeras: una herramienta clave para el aprendizaje

El presente trabajo se propone realizar un estudio acerca de la conceptualización, análisis y tratamiento de los errores en los procesos de enseñanza y aprendizaje de una lengua segunda (L2) en sujetos bilingües. La expresión aprendizaje de segundas lenguas se usará para referir al conjunto de procesos conscientes e inconscientes por los cuales el aprendiz logra adquirir cierto nivel de competencia en una L2. En este sentido, contrario a lo que las primeras teorías de adquisición de lenguas extranjeras han sostenido acerca de desterrar el error, se intentará demostrar que éste es un paso fundamental que forma parte del verdadero aprendizaje de una lengua. Para ello, revisaremos brevemente diversas definiciones de 'error' postuladas por distintas corrientes y teorías del aprendizaje a lo largo de los últimos cien años. Además, cuestionaremos nuestro rol como docentes a la hora de marcar errores: ¿Cómo nos posicionamos frente al error? ¿Somos esenciales para que el alumno pueda detectar y corregir sus desaciertos? Nos preguntaremos también si el conocimiento de normas propias de la lengua materna favorece el aprendizaje de una L2. Para tratar de responder a estas preguntas, hemos consultado una serie de autores como Blanco Picado, Corder, Coyle y Klein y realizado una encuesta a profesores de lenguas extranjerasFacultad de Humanidades y Ciencias de la Educació