Biological and molecular characterization of a resistance-breaking isolate of citrus tristeza virus from Uruguay and its effects on Poncirus trifoliata growth performance.

Resistance-breaking (RB) isolates of citrus tristeza virus (CTV) can replicate and move systemically in Poncirus trifoliata, a rootstock widely used for management of decline caused by CTV and other purposes. In Uruguay, severe CTV isolates are prevalent, and an RB isolate (designated as RB-UY1) was identified. In order to predict the implications of this genotype circulating in citrus crops grafted on trifoliate rootstocks, the aim of this work was to determine the biological and molecular characteristics of this isolate, the efficiency of its transmission by Toxoptera citricida, and its effects on plant growth performance of P. trifoliata. Our results show that RB-UY1 can be classified as a mild isolate, that it is phylogenetically associated with the RB1 group, and that it is efficiently transmitted by T. citrida. They also suggest that the RB-UY1 isolate should not affect the performance of citrus crops grafted on trifoliate rootstocks, although some growth parameters of P. trifoliata seedlings were affected four years after inoculation.

Complete Genome Sequence of a Novel Recombinant Citrus Tristeza Virus, a Resistance-Breaking Isolate from Uruguay.

We report here the complete genome sequence of a Citrus tristeza virus (CTV) from Uruguay, sequenced by using Illumina and Sanger sequencing technology. This CTV DSST-17 genome clustered within genotype resistance breaking (RB) and presents two recombination events.

Phylogenetic Studies of the Three RNA Silencing Suppressor Genes of South American CTV Isolates Reveal the Circulation of a Novel Genetic Lineage.

Citrus Tristeza Virus (CTV) is the most economically important virus of citrus worldwide. Genetic diversity and population structure of CTV isolates from all citrus growing areas from Uruguay were analyzed by RT-PCR and cloning of the three RNA silencing suppressor genes (p25, p20 and p23). Bayesian phylogenetic analysis revealed the circulation of three known genotypes (VT, T3, T36) in the country, and the presence of a new genetic lineage composed by isolates from around the world, mainly from South America. Nucleotide and amino acid identity values for this new genetic lineage were both higher than 97% for the three analyzed regions. Due to incongruent phylogenetic relationships, recombination analysis was performed using Genetic Algorithms for Recombination Detection (GARD) and SimPlot software. Recombination events between previously described CTV isolates were detected. High intra-sample variation was found, confirming the co-existence of different genotypes into the same plant. This is the first report describing: (1) the genetic diversity of Uruguayan CTV isolates circulating in the country and (2) the circulation of a novel CTV genetic lineage, highly present in the South American region. This information may provide assistance to develop an effective cross-protection program.

Diverse population of a new bipartite begomovirus infecting tomato crops in Uruguay.

Several isolates of a novel begomovirus were characterized from tomato samples collected in northern Uruguay exhibiting disease symptoms associated with Bemisia tabaci infestations. Analysis of full-length sequences of DNA-A and DNA-B components revealed the presence of a new begomovirus with the typical genome organization of a New World begomovirus, for which the name tomato rugose yellow leaf curl virus (ToRYLCV) is proposed. A high degree of nucleotide sequence diversity was found for both components, suggesting the presence of a diverse virus population. Recombination analysis suggested relationships of ToRYLCV to begomoviruses reported from the New World. Although common regions from DNA-As and DNA-Bs were surprisingly divergent for a cognate pair, a DNA-A and DNA-B pair cloned from one sample were infectious in Nicotiana benthamiana and tomato and reproduced symptoms observed in field-infected tomato plants, suggesting that ToRYLCV is the causal agent of the disease observed. This is the first report of a begomovirus infecting tomato crops in Uruguay and of the presence of begomovirus in this country.

Pesticide dissipation curves in peach, pear and tomato crops in Uruguay.

Dissipation curves of azoxystrobin and of the neonicotinoids acetamiprid and thiacloprid in peach; azinphos-methyl and carbaryl in pear and azoxystrobin, chlorfenapyr and chlorpyrifos in high-tunnel tomato crops were studied in the Southern region of Uruguay. An analytical methodology based on solid phase extraction (SPE) and detection by High Performance Liquid Chromatography with Diode Array Detector (HPLC/DAD) was used for acetamiprid and thiacloprid. Coupled SPE and detection by Gas Chromatography with Mass Selective Detector (GC/MSD) was used for the detection of azinphos-methyl, azoxystrobin, carbaryl, chlorfenapyr and chlorpyrifos residues. Curves were modeled mathematically with Solver program of Microsoft Excel. The best fit for acetamiprid and thiacloprid in peach was achieved with the exponential model (r(2)=0.961 and 0.944, respectively). In the case of peach fruits there is not a Maximum Residue Limit (MRL) for acetamiprid in the Codex Alimentarius, while 0.5 mg/kg is the value rated for thiacloprid. The MRLs accepted by the European Union (EU) are 0.1 mg/kg for acetamiprid and 0.3 mg/kg for thiacloprid. According to the curves determined in these experiments, thiacloprid residues 10 to 12 days after application (daa) were below the MRLs established by both sources. In the case of acetamiprid, 25 daa would be required, according to the exponential mathematical model, to get residues levels below the MRL values established by the EU. For azinphos methyl in pear, the residues detected were mathematically fitted to an exponential model (r(2)=0.999). According to it, residue levels under the MRL established by the EU (0.05 mg/kg) are gotten in our conditions in 20 daa. In plastic tunnel tomato chlorfenapyr residues were not detected from 16 daa, having the dissipation curve an exponential trend. In the same condition, there was not a decay of the azoxystrobin concentration during a 24-day trial, being it around 0.40 ± 0.05 mg/kg.