Effects of Aphid Transmission on the Structure of a Mild and a Severe Citrus Tristeza Virus Population from Italy (original) (raw)
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Diversity of Uruguayan citrus tristeza virus populations segregated after single aphid transmission
Tropical Plant Pathology, 2019
Prevalence of citrus tristeza virus (CTV) isolates causing severe stem pitting symptoms with a high diverse genetic composition represents a threat for citrus crops in Uruguay. This work aimed to characterize viral components of CTV populations segregated by single aphid (Toxoptera citricida) transmission (SAT). Thirty-nine SAT-derived sub-isolates were obtained from six CTV field isolates. Only eight were MCA13 non-reactive, and six of them, together with other three MCA13 reactive sub-isolates, were considered mild by the intensity of their reaction in 'Mexican' lime, 'Madam Vinous' sweet orange, 'Duncan' grapefruit and sour orange indicator plants. Fourteen sub-isolates, including two MCA13 non-reactive, were considered moderate, and the remaining sub-isolates were all MCA13 reactive and with severe reactions in the indicator plants. Sequence comparisons of the p20, p23 and p25 genes showed a high inter (among all isolates and their derived sub-isolates)-and intra (among each isolate and its derived sub-isolates)-specific evolutionary diversity, with the presence of the CTV strains VT, T3, RB, and NC in mixtures of their complex populations. Together, our data revealed the heterogeneity of the Uruguayan CTV populations in these CTV field isolates. The results provide additional biological and molecular information on the complex CTV populations in Uruguay and must be considered for improving the CTV management program.
Virology, 1999
Genetic variability of citrus tristeza virus (CTV) was studied using the haplotypes detected by single-strand conformation polymorphism (SSCP) analysis of genes p18 and p20 in six virus populations of two origins. The Spanish group included a CTV isolate and subisolates obtained by graft-transmission to different host species. The other included two subisolates aphid-transmitted from a single Japanese isolate. The homozygosity observed for gene p20 was always significantly higher than that expected under neutral evolution, whereas only three populations showed high homozygosity for p18, suggesting stronger host constraints for p20 than for p18. Sequential transmissions of a Spanish isolate to new host species increased the difference between its population and that of the successive subisolates for gene p18, as estimated by the F statistic. Analysis of molecular variance indicated that variation between both groups of populations was not statistically significant, whereas variations between populations of the same group or within populations were significant for both genes studied. Our data indicate that selection affects the haplotype distribution and that adaptation to a new host can be as important or more as the geographical origin. Variation of the CTV populations after host change or aphid transmission may explain in part the wide biological variability observed among CTV isolates.
Phytopathologia Mediterranea
Phylogenetic analyses categorize seven genotypes of citrus tristeza virus (CTV). The symptoms caused by this pathogen, their expression and severity are influenced by CTV genotypes, host species, cultivars, and infected host rootstocks. This study aimed to verify how populations of Chilean CTV isolates changed following inoculation from infected sweet orange to Mexican lime trees, and to determine if CTV genotype populations influenced transmission efficiency via Aphis gossypii. Reverse transcription polymerase chain reaction showed variation in genotypes of populations of CTV in Mexican lime, after graft inoculations using infected sweet orange chip-buds. Severe genotypes (VT) were detected after inoculation of mild isolate CTV populations (T30). The T30 donor populations also reduced transmissibility via A. gossypii; however, these results may not be conclusive due to mixture with the VT genotype. There is evidence of high rates of virus acquisition by this aphid species, but also...
European Journal of Plant Pathology, 2014
The evolution of citrus tristeza virus (CTV) from outbreaks occurred in Calabria, Italy, was compared with that of CTVoutbreaks reported previously in another two proximal Italian regions, Sicily and Apulia. Examination of four genomic regions (genes p20, p25 and p23, and one fragment of open reading frame 1) showed two recombination events, and phylogenetic analysis disclosed two divergent CTV groups in Calabria: one formed by severe and the other by mild isolates. This analysis, together with others involving population genetic parameters, revealed a low migration rate of CTV between the three Italian regions, as well as significant differences in selective pressures, epidemiology and demography, all affecting the genetic structure of CTV populations.
Emergence and Phylodynamics of Citrus tristeza virus in Sicily, Italy
PLoS ONE, 2013
Citrus tristeza virus (CTV) outbreaks were detected in Sicily island, Italy for the first time in 2002. To gain insight into the evolutionary forces driving the emergence and phylogeography of these CTV populations, we determined and analyzed the nucleotide sequences of the p20 gene from 108 CTV isolates collected from 2002 to 2009. Bayesian phylogenetic analysis revealed that mild and severe CTV isolates belonging to five different clades (lineages) were introduced in Sicily in 2002. Phylogeographic analysis showed that four lineages co-circulated in the main citrus growing area located in Eastern Sicily. However, only one lineage (composed of mild isolates) spread to distant areas of Sicily and was detected after 2007. No correlation was found between genetic variation and citrus host, indicating that citrus cultivars did not exert differential selective pressures on the virus. The genetic variation of CTV was not structured according to geographical location or sampling time, likely due to the multiple introduction events and a complex migration pattern with intense co-and recirculation of different lineages in the same area. The phylogenetic structure, statistical tests of neutrality and comparison of synonymous and nonsynonymous substitution rates suggest that weak negative selection and genetic drift following a rapid expansion may be the main causes of the CTV variability observed today in Sicily. Nonetheless, three adjacent amino acids at the p20 N-terminal region were found to be under positive selection, likely resulting from adaptation events.
Journal of General Plant …, 2010
The nucleotide sequences for the minor coat protein (CPm) gene and its deduced amino acid sequences for two aphid-transmissible and two nontransmissible isolates of Citrus tristeza virus (CTV) from symptomless orchard trees of Miyagawa satsuma [Citrus unshiu (Macf.) Marc.] on trifoliate orange [Poncirus trifoliate (L.) Raf.] and declining Washington navel [C. sinensis (L.) Osb.] trees on sour orange (C. aurantium L.) rootstocks were analyzed and compared with those of highly transmissible CTV strains available in GenBank. The isolates produced severe symptoms on indicator plants and their aphid transmissibility was assayed through acquisition by A. gossypii of CTV and subsequent inoculation feeding on young Mexican lime seedlings. The CPm gene nucleotides and coded amino acid sequences were very similar among the nontransmissible isolates and among the transmissible. Five of 73 nucleotide substitutions that existed between CPm gene nucleotide sequence of nontransmissible and transmissible isolates caused changes in the deduced amino acid sequences of the nontransmissible isolates. Two nucleotide substitutions yielded new amino acids with similar properties. However, the three remaining mutations led to substitution of new amino acids with a different charge and polarity at positions 14, 238 and 239. The last two mutations occurred at the C-terminal region of the CPm, which is implicated in the formation of a salt bridge that helps to maintain the protein's tertiary structure. Amino acid substitutions can affect aphid transmission efficiency by altering the conformation of the proteins or masking motifs involved in the interaction between CPm and aphid stylets. Keywords Citrus tristeza virus Á Minor coat protein Á Aphid transmissibility Á Aphis gossypii
Frontiers in Plant Science
Grapefruit trees in South Africa have been cross protected against severe stem pitting genotypes of Citrus tristeza virus (CTV) since the 1920s using a mild strain initially called ‘Nartia’ but later referred to as grapefruit mild strain 12 (GFMS12). In the current study, the GFMS12 isolate was used as the source for single aphid transmissions (SAT) using Toxoptera citricida, commonly called the brown citrus aphid (BrCA). The BrCA-transmitted CTV sub-isolates were analyzed by the heteroduplex mobility assay (HMA), serological assays, genetic marker analysis (GMA), and selected sub-isolates were biologically indexed. Reverse transcription PCR of genomic regions was conducted using universal primers followed by cloning the PCR products, HMA and sequence analysis; nine genotypes of CTV were identified in the complex of GFMS12, including both severe and mild genotypes. A single BrCA transmitted up to six CTV genotypes simultaneously in one sub-isolate. The HMA was found to be a rapid, r...
Phytopathologia Mediterranea, 2010
Since 2006 a survey on Citrus tristeza virus (CTV) has been carried out in Calabria , southern Italy , to determine the occurrence of the virus, to evaluate its incidence, to identify and characterize the virus strains, and to monitor the aphid vector populations. Citrus samples were collected from nurseries and orchards located in the five provinces of the region. The virus was not detected in the citrus-growing areas of Catanzaro (CZ) or Crotone (KR), whereas it was found in three orchards in Cosenza (CS), three in Vibo Valentia (VV) and twelve citrus plantings in Reggio Calabria (RC). The highest infection percentages occurred in citrus orchards close to fields already infected with CTV. Infections were detected not only in foreign cultivars, but also in local cultivars such as ‘Comune’ clementine, ‘Moro’, ‘Ovale’ and ‘Tarocco’ sweet orange, suggesting that CTV was transmitted by aphids. CTV occurred in only a few plantlets sampled in two citrus nurseries located near the main ar...
Epitope Diversity of Citrus Tristeza Virus Isolates in Spain
Fifty-nine Spanish citrus tristeza virus (CTV) isolates from the IVIA collection were tested against nine CTV-specific monoclonal antibodies (MCAs) by double antibody sandwich indirect ELISA (ELISA-DASI). Six different epitopes were detected, and seven distinct serogroups were defined by their reaction pattern with the different MCAs. Five of the MCAs recognized all Spanish CTV sources tested. Changes in epitope composition, observed in someisolates after aphid transmission or after propagation in certain hosts and graft transmission, indicated that some field isolates are mixtures of strains. The analysis of 1,613 CTV-infected trees collected from areas with variable CTV incidence showed that up to 18% of the samples from trees in heavily infested areas (>80% incidence) reacted with all MCAs, whereas all samples from areas with less than 2% CTV incidence failed to react with some MCAs. This suggests that mixtures of strains are more abundant in areas where CTV has been established for a long time. The analysis of 3,231 CTV-infected trees by ELISA-DAS with MCAs 3DF1,3CA5, and MC13 showed that only 8.7% reacted with MCl3, whereas 99.6 %reacted with 3DF1 and 100% with 3CA5. A mixture of 3DF1 and 3CA5 detected all isolates. Under Spanish conditions, the reaction with MC13 was not correlated with the decline of trees on sour orange in the field. However, all known severe strains reacted with MC13 and 10E3 antibodies.