Wheat antixenosis, antibiosis, and tolerance to infestation by Delphacodes kuscheli (Hemiptera: Delphacidae), a vector of "Mal de Río Cuarto" in Argentina.

"Mal de Rio Cuarto", is the most important virus disease of corn, Zea mays L., in Argentina. It is caused by the Mal de Rio Cuarto virus (family Reoviridae, genus Fijivirus. MRCV), which is a persistent virus transmitted by Delphacodes kuscheli (Fennah 1955) (Hemiptera: Delphacidae). Because corn is not a natural host of D. kuscheli, it has little protection from this pest. In contrast, wheat, Triticum aestivum L., is one of the main hosts of this vector and a reservoir of MRCV. The aim of this work was to identify genes involved in antixenosis, antibiosis, and tolerance of infestation by D. kuscheli in wheat, which might be used to reduce the population level of this vector on corn. A set of recombinant dihaploid (RDH) lines for chromosome 6A derived from the F1 cross between 'Chinese Spring' (CS) X 'Chinese Spring (Synthetic 6A)' (S6A) substitution line, was used for mapping. The S6A parental line is resistant to the MRCV vector. Antixenosis, antibiosis, and tolerance were evaluated using conventional tests in controlled environmental conditions. Most of the RDH and S6A showed higher levels of antixenosis against D. kuscheli than the parental line CS. The RDH lines showed highly significant antibiosis in terms of the duration of first, third, and fifth nymphal instars, developmental time (days), survival and fecundity. There were highly significant differences in the tolerance to D. kuscheli based on the chlorophyll content of the first and second leaves, foliar area, and aboveground fresh and dry weights. The duration of the fifth nymphal instar and the developmental period were significantly associated with Xgwm1017 marker loci, located at 48 cM on 6AL. Another quantitative trait locus accounting for the variation in chlorophyll content of the first leaf was associated with the interval between loci Xgwm459 and Xgwm334a, located in the telomeric region of the 6AS chromosome arm. The alleles with positive effects came from S6A. Antibiotic resistance of RDH could be useful for controlling the population increase of the MRCV vector on wheat, because prolonging the duration of development increases the period between two subsequent generations, so reducing the abundance of infective populations colonizing corn.

Sipha maydis: distribution and host range of a new aphid pest of winter cereals in Argentina.

Sipha maydis (Passerini) is a new aphid pest of cereals and cultivated and wild grasses in Argentina. This species was recently introduced into America, and nothing is known of its distribution or host range in South America. A better understanding of its biology is likely to facilitate control. This article records 1) the distribution and 2) the host range of S. maydis in Argentina. Over the period 2004-2006 samples were collected from 32 populations at several localities in Argentina. The number of S. maydis, accompanying aphid species, and the host from which they were collected were recorded. The distribution of S. maydis ranged from 32 degrees 52' to 42 degrees 03' S, and from 57 degrees 41' to 71 degrees 24' W, bounded by isothermals 18 and 10 degrees C and isohyets 200-400 and <1,200 mm. No S. maydis were found in the subtropical region, even in winter. In the field, the different populations showed very different host preferences. S. maydis was found mainly on cultivated barley and wheat and on wild Bromus spp. and Sorghum halepense (L.) Pers. No aphids were found on maize, Zea mays L. Most of the damage to winter cereal crops occurred at the seedling stage in early autumn and of adult plants when infestations occurred in late spring. In the 4 yr after the first record of S. maydis in Argentina, it colonized a huge area similar to that colonized by Diuraphis noxia (Mordvilko) in 10 yr. The wide range of regions, hosts and climatic conditions this species is adapted to is likely to make the control of this pest very difficult.

Serial analysis of gene expression (SAGE) of host-plant resistance to the cassava mosaic disease (CMD).

Cassava mosaic disease (CMD) is a viral disease of the important tropical staple crop cassava (Manihot esculenta) and preferred management involves use of host-plant resistance. The best available resistance is controlled by a single dominant gene. Serial analysis of gene expression (SAGE) was used to analyze the gene expression pattern in a bulk of 40 each of CMD resistant and susceptible genotypes drawn from a gene mapping progeny. Messenger RNA used for the SAGE analysis came from plants that were exposed to heavy disease pressure over a period of 2 years in the field. A total of 12,786 tags were studied, divided into 5733 and 7053 tags from the resistant and susceptible genotypes, respectively. Tag annotation was by PCR amplification using the tag sequence as sense primer and 4000 cassava ESTs generated from the bulk of CMD resistant genotypes. Annotation of more than 30 differentially expressed tags revealed several genes expressed during systemic acquired resistance (SAR) in plants and other genes involved in cell-to-cell and cytoplasm-to-nucleus virus trafficking. Differential expression of the most abundantly expressed tag, corresponding to a beta-tubulin gene, was confirmed by Northern Analysis. RFLP analysis of the tags in the parents and bulks of the CMD mapping progeny revealed only one tag, a WRKY transcription factor, associated with the region bearing the dominant CMD gene.

Simple sequence repeat marker diversity in cassava landraces: genetic diversity and differentiation in an asexually propagated crop.

Cassava (Manihot esculenta) is an allogamous, vegetatively propagated, Neotropical crop that is also widely grown in tropical Africa and Southeast Asia. To elucidate genetic diversity and differentiation in the crop's primary and secondary centers of diversity, and the forces shaping them, SSR marker variation was assessed at 67 loci in 283 accessions of cassava landraces from Africa (Tanzania and Nigeria) and the Neotropics (Brazil, Colombia, Peru, Venezuela, Guatemala, Mexico and Argentina). Average gene diversity (i.e., genetic diversity) was high in all countries, with an average heterozygosity of 0.5358 +/- 0.1184. Although the highest was found in Brazilian and Colombian accessions, genetic diversity in Neotropical and African materials is comparable. Despite the low level of differentiation [F(st)(theta) = 0.091 +/- 0.005] found among country samples, sufficient genetic distance (1-proportion of shared alleles) existed between individual genotypes to separate African from Neotropical accessions and to reveal a more pronounced substructure in the African landraces. Forces shaping differences in allele frequency at SSR loci and possibly counterbalancing successive founder effects involve probably spontaneous recombination, as assessed by parent-offspring relationships, and farmer-selection for adaptation.

Cognitive therapy for the management of sickle cell disease pain: an evaluation of a community based intervention

Sickle cell disease [SCD] is the most prevalent haemoglobinopathy in Northern Europe [WHO, 1985]. It primarily affects the Caribbean and African population as well as small numbers of people from Mediterranean and India [NAHAT,19991]. SCD's most common symptoms is the vaso-occlusive cricis or "painful cricis". Painful crises are the principal cause of morbidity among patients with SCD and account for the second greatest number of hospital admissions with an average of seven days. Whilst numbers vary, most patient experience at least one severe episode per year requiring hospital admission for control. This inevitably causes severe disruption to educational and social aspects of patients' lives, which in turn, has consequences for achievement capabilities and psycho-social adjustment[Thomas and Westerdale,1996]. Nevertheless, traditionally the focus of treatment for SDC pain has been upon its physical aspects.This has been at the expense of consideration of the psycho-social and socio-cultural factors involved and may account for some of the difficulties fraught within the current treatment for SCD pain. [AU]