We show that a sonic crystal made of periodic distributions of rigid cylinders in air acts as a new material which allows the construction of refractive acoustic devices for airborne sound. It is demonstrated that, in the long-wave regime, the crystal has low impedance and the sound is transmitted at subsonic velocities. Here, the fabrication and characterization of a convergent lens are presented. Also, an example of a Fabry-Perot interferometer based on this crystal is analyzed. It is concluded that refractive devices based on sonic crystals behave in a manner similar to that of optical systems.

Tomato spotted wilt virus (TSWV) causes severe economic losses in many crops worldwide and often overcomes resistant cultivars used for disease control. Comparison of nucleotide and amino acid sequences suggested that tomato resistance conferred by the gene Sw-5 can be overcome by the amino acid substitution C to Y at position 118 (C118Y) or T120N in the TSWV movement protein, NSm. Phylogenetic analysis revealed that substitution C118Y has occurred independently three times in the studied isolates by convergent evolution, whereas the substitution T120N was a unique event. Analysis of rates of non-synonymous and synonymous changes at individual codons showed that substitution C118Y was positively selected.Tomato spotted wilt virus (TSWV) is one of the most economically important plant viruses and causes damage in many agronomic crops worldwide (Adkins, 2000). TSWV is the type member of the genus Tospovirus, which contains the only plant-infecting members of the family Bunyaviridae. The genome consists of three negative-sense or ambisense RNA segments: segment L encodes a putative RNAdependent RNA polymerase (de Haan et al., 1991); segment M encodes the cell-to-cell movement protein, NSm (Li et al., 2009), and the precursor of the surface glycoproteins, G N / G C , involved in TSWV transmission by thrips (Sin et al., 2005;Naidu et al., 2008); and segment S encodes a silencing suppressor, NSs (Takeda et al., 2002), and the nucleocapsid, N (de Haan et al., 1990).Controlling TSWV in crop plants has proven difficult because of the wide range of plant hosts (.1000 species) and effective spread of TSWV by thrip vectors (Hanssen et al., 2010). Intense efforts have been made around the world to obtain genetically resistant cultivars against TSWV. Only the dominant genes Sw-5 and Tsw introgressed in tomato (Lycopersicon esculentum, 5Solanum lycopersicum) and pepper (Capsicum annuum) cultivars, respectively, have been found to confer resistance to a wide spectrum of TSWV isolates; they have been deployed in commercial cultivars worldwide. Sw-5 is also effective against two other tospoviruses, Tomato chlorotic spot virus (TCSV) and Groundnut ringspot virus (GRSV) (Soler et al., 2003). However, Sw-5 resistance-breaking (SRB) isolates have been detected in Hawaii, Australia, South Africa, Spain and Italy (Cho et al., 1996;Thompson & van Zijl, 1996;Latham & Jones, 1998;Aramburu & Martí, 2003;Ciuffo et al., 2005) and Tsw resistance-breaking (TRB) isolates have been detected in Brazil, USA, Italy, Spain and Australia (Boiteux et al., 1993;Hobbs et al., 1994;Roggero et al., 2002; Margaria et al., 2004;Sharman & Persley, 2006).Understanding the molecular mechanisms linked to resistance breakdown and the evolutionary processes involved in the emergence of resistance-breaking isolates is a major challenge. This is relevant to the development of more durable and efficient resistance, which would certainly have a considerable economic impact on agriculture. Since a reverse-genetics system based on infectious cDNA clones is not availab...

The first Citrus tristeza virus (CTV) genomes completely sequenced (19.3-kb positive-sense RNA), from four biologically distinct isolates, are unexpectedly divergent in nucleotide sequence (up to 60% divergence). Understanding of whether these large sequence differences resulted from recent evolution is important for the design of disease management strategies, particularly the use of genetically engineered mild (essentially symptomless)-strain cross protection and RNA-mediated transgenic resistance. The complete sequence of a mild isolate (T30) which has been endemic in Florida for about a century was found to be nearly identical to the genomic sequence of a mild isolate (T385) from Spain. Moreover, samples of sequences of other isolates from distinct geographic locations, maintained in different citrus hosts and also separated in time (B252 from Taiwan, B272 from Colombia, and B354 from California), were nearly identical to the T30 sequence. The sequence differences between these isolates were within or near the range of variability of the T30 population. A possible explanation for these results is that the parents of isolates T30, T385, B252, B272, and B354 have a common origin, probably Asia, and have changed little since they were dispersed throughout the world by the movement of citrus. Considering that the nucleotide divergence among the other known CTV genomes is much greater than those expected for strains of the same virus, the remarkable similarity of these five isolates indicates a high degree of evolutionary stasis in some CTV populations.

Cucurbits are major crop species, including fruits and vegetables cultivated worldwide that supply essential vitamins and minerals to current diets in developed and developing countries. Viral diseases are main factors affecting cucurbits cultivation. The most widespread and damaging have been aphidborne viruses belonging to the Potyviridae family. Whitefly-transmitted begomoviruses (Geminiviridae) have been identified more recently in different cucurbit species. A severe outbreak of Tomato leaf curl New Delhi virus (ToLCNDV) occurred in pumpkins and melons in the main production area of Southern Spain in 2012-2014. We developed a mechanical inoculation method to facilitate the screening of germplasm against this virus. Mechanical transmission with this method was confirmed in 4 genera and 13 species of the family, including the main crops, cucumber, melon, watermelon and pumpkins, and also croprelated exotic germplasm (landraces and wild species) used for cucurbits breeding. Diversity in the response was observed within and among species. Tolerance to mechanical transmission of ToLCNDV was identified in melon, within Cucumis melo subsp. agrestis var. momordica and in wild agrestis accessions. All the tolerant accessions came from India, the country in which this virus was firstly reported. Some of these accessions have been previously reported to be tolerant or resistant to other viruses and as they are fully crossable to commercial melons, they are good sources to develop new melon varieties with tolerance to ToLCNDV.

Ectopic expression of the p23 gene from a severe (T36) strain of Citrus tristeza virus (CTV) induces viral-like symptoms in Mexican lime. Here, we report that expressing the same gene from a mild strain induced similar symptoms that correlated with accumulation of p23 protein irrespective of the source strain. CTV inoculation of transgenic limes showing CTV-like leaf symptoms and high p23 accumulation did not modify symptoms initially, with the virus titer being as in inoculated nontransgenic controls; however, at later stages, symptoms became attenuated. Transformation with p23-T36 of CTV-susceptible sweet and sour orange and CTV-resistant trifoliate orange also led to CTV-like leaf symptoms that did not develop when plants were transformed with a truncated p23 version. In transgenic citrus species and relatives other than Mexican lime, p23 was barely detectable, although symptom intensity correlated with levels of p23 transcripts. The lower accumulation of p23 in sweet and sour orange compared with Mexican lime also was observed in nontransgenic plants inoculated with CTV, suggesting that minimal p23 levels cause deleterious effects in the first two species. Conversely, transgenic expression of p23 in CTV nonhost Nicotiana spp. led to accumulation of p23 without phenotypic aberrations, indicating that p23 interferes with plant development only in citrus species and relatives.

Isolates of citrus tristeza virus (CTV) differ widely in their biological properties. These properties may depend on the structure of viral RNA populations comprising the different isolates. As a first approach to study the molecular basis of the biological variability, we have compared the sequences of multiple cDNA clones of the two terminal regions of the RNA from different CTV isolates. The polymorphism of the 5' untranslated region (UTR) allowed the classification of the sequences into three groups, with intragroup sequence identity higher than 88% and intergroup sequence identity as low as 44%. The variability of an open reading frame (ORF) 1a segment adjacent to the 5' UTR supports the same grouping. Some CTV isolates contained sequences of more than one group. Most sequences from Spanish isolates belonged to group III, whereas a Japanese isolate was composed mostly of sequences of groups I and II. The mildest isolates contained only sequences of group III, whereas the most severe isolates also contained sequences of groups I, II, or both. The most stable secondary structure predicted for the 5' UTR was composed of two stem-loops and remained essentially unchanged as a result of compensatory mutations in the stems and accommodation of most of the variability in the loops. In contrast to the 5'-terminal region, the variability of the 3'-terminal region of CTV RNA was very much restricted, with nucleotide identity values higher than 90%. The presence of a conserved putative "zinc-finger" domain adjacent to a basic region in p23, the predicted product of ORF 11, suggests that this protein might act as a regulatory factor during virus replication.

In this paper, we report experiments on the scattering of surface-elastic waves by a periodic array of cylindrical holes. The experiments were performed in a marble quarry by drilling cylindrical holes in two different configurations: honeycomb and triangular lattices. The attenuation spectra of the surface waves show the existence of absolute band gaps for elastic waves in these semi-infinite two-dimensional crystals. Results are compared with theoretical calculations based on a scalar-wave approach. The scaling property of the underlying theory has led us to explore the possible application of the results obtained to the attenuation of surface waves in seismic movements. ͓S0163-1829͑99͒07419-6͔

Summary The 23 kDa protein (p23) coded by the 3′‐terminal gene of Citrus tristeza virus (CTV), a member of the genus Closterovirus with the largest genome among plant RNA viruses, is an RNA‐binding protein that contains a motif rich in cysteine and histidine residues in the core of a putative zinc‐finger domain. On this basis, a regulatory role for CTV replication or gene expression has been suggested for p23. To explore whether over‐expression of this protein in transgenic plants could affect the normal CTV infection process, transgenic Mexican lime plants were generated carrying the p23 transgene, or a truncated version thereof, under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Constitutive expression of p23 induced phenotypic aberrations that resembled symptoms incited by CTV in non‐transgenic lime plants, whereas transgenic plants expressing the p23 truncated version were normal. The onset of CTV‐like symptoms in p23‐transgenic plants was associated with the expression of p23, and its accumulation level paralleled the intensity of the symptoms. This demonstrates that p23 is involved in symptom development and that it most likely plays a key role in CTV pathogenesis. This is the first case in which a protein encoded by a woody plant‐infecting RNA virus has been identified as being directly involved in pathogenesis in its natural host. This finding also delimits a small region of the large CTV genome for the future mapping of specific pathogenic determinants.