Evidence supporting the recognition of Cole latent virus as a distinct carlavirus

Some molecular properties are described of Cole latent virus (CoLV), hitherto designated a tentative species of the Carlavirus genus. CoLV genomic RNA (Ribonucleic acid) of 8.3 Kb is polyadenylated. Two unencapsidated polyadenylated subgenomic RNAs (2.6 and 1.3 Kb) and three double-stranded RNAs (dsRNAs) (8.3, 2.6 and 1.3 Kbp), which are twice the size of the genomic and subgenomics ssRNAs, are produced in CoLV-infected plants, two additional dsRNAs (7.2 and 6.3 Kbp) were also detected plant extracts. By using a Carlavirus specific primer and a CoLV cDNA, a-3'-terminus fragment of 116 bp was amplified; it had homology with the carlaviruses Potato virus M (62%)., Hop latent virus (37%) and Blueberry scorch virus (36%) but no significant homology with 11 other carlaviruses. These results support the classification of CoLV as a distinct species of the Carlavirus genus

PHYLOGENETIC RELATIONSHIP OF ZEINS AND COIXINS AS DETERMINED BY IMMUNOLOGICAL CROSS-REACTIVITY AND SOUTHERN BLOT ANALYSIS

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Genotypic diversity of Citrus tristeza virus within red grapefruit, in a field trial site in South Africa

Grapefruit cultivars (Citrus paradisi Macfad.) are extremely sensitive to Citrus tristeza virus (CTV) infections and are pre-immunized with mild-strain crossprotecting sources not containing components that elicit symptoms such as stempitting and decline, to ensure longer periods of productivity. However, preimmunizing sources often lose their efficiency and for this reason the previously commercially applied grapefruit cross-protecting source GFMS (grapefruit mildstrain) 12 has been replaced by GFMS 35. This study was undertaken to determine the diversity of CTV genotypes within trees that were inoculated with either GFMS 12 or GFMS 35. Samples were collected from a number of different trees of two red grapefruit cultivars (cv. Star Ruby and cv. Flame), planted 10 years prior to sampling in the Malelane production area of South Africa. Reverse transcription-polymerase chain reaction amplification of a 5‘ variable region (A-region) and a 3‘ conserved region (p23 gene) was followed by cloning, sequencing of multiple clones and phylogenetic analyses. The genotypic identities of clones were determined based on their relatedness to reference CTV strains. Sequence types within the VT genotypic group dominated in all of the samples, with T30-like sequence types being a minor component in some populations of the field collected samples. The original preimmunising populations of GFMS 12 and GFMS 35 were characterised on greenhouse maintained plants and compared with the populations exposed to field infections by aphids. While the methodology employed only allows a coarse representation of the genotype composition of the CTV population, this study provides insight into which genotypes of CTV must be incorporated within a mildstrain cross-protecting source within the South African Citrus Improvement Scheme (SACIS).Citrus Research International, Agricultural Research Council-Plant Protection Research Institute and the National Research Foundation-THRIP program.http://link.springer.com/journal/106582016-07-30hb201

Genetic tools and strategies for citrus breeding aiming at resistant rootstocks to gummosis disease

Phytophthora nicotianae Breda de Haan (syn. Phytophthora parasitica Dastur), causal agent of citrus gummosis disease, has caused great damage to citrus orchards throughout the world. While chemical and horticultural measures do not guarantee the preventive or curative control of citrus gummosis, the use of resistant rootstocks is the most reliable management strategy against the disease. Aiming at the development of citrus rootstocks resistant to gummosis and to better elucidate the Phytophthora-citrus pathosystem, citrus breeding programs have been ongoing worldwide, mostly employing directed crosses. These studies have succeeded in identifying differences in symptom development between resistant and susceptible rootstocks, as well as in the progeny of their crosses. In addition, differentially expressed genes were assessed, which ultimately should lead to the identification of markers involved in resistance to P. nicotianae. In this review we summarize the current knowledge of the molecular basis of citrus gummosis and the main strategies employed to obtain genetically resistant rootstocks.Biotechnology Lab Instituto Agronômico de Campinas Centro APTA Citros Sylvio Moreira, Caixa Postal 04Departamento de Genética Instituto de Biociências UNESP, Caixa Postal 510Department of Entomology and Plant Pathology Auburn UniversityDepartamento de Genética Instituto de Biociências UNESP, Caixa Postal 51