Severe <i>Citrus tristeza virus</i> Isolates from Eastern Mexico Are Related to the T36 Genotype Group

Abstract

Citrus tristeza virus (CTV) outbreaks have been reported in the main citrus growing region of Mexico in the past four years. Recently, in eastern Mexico (the major citrus-growing region in the country), severe CTV isolates have been detected. However, the molecular identity of observed isolates remains unestablished. This research was undertaken to elucidate the molecular characterization of CTV populations spreading in this region and to compare it with phylogeny of existing isolates. Genotyping of 32 collected isolates was performed using reverse-transcription polymerase chain reaction (RT-PCR) with sequence analysis of the coat protein (CP) gene, putatively associated with pathogenicity. This protein is a 25 kDa major capsid protein, which forms a long virion body coating 95% of the particle length. A comparative sequence analysis was performed using CTV sequences from different geographical origins already published and deposited in the GenBank databases. Phylogenetic analysis showed that the degree of sequence divergence among isolates correlated with their pathogenicity. Based on the sequencing results, the collected isolates were categorized as mild or severe phylogenetic clusters, each being genetically distinct. The severe group was associated with either alike or with a T36-like genotype. The latter group matched with the quick decline and stem pitting drastic symptoms observed in the field. This study

Transcriptomic Analysis of the Host Response to Mild and Severe CTV Strains in Naturally Infected Citrus sinensis Orchards

“…On the other hand, the downregulation of Argonaute-1 (AGO1) mRNA only occurred in response to severe CTV infection. Clearly, more studies are required to determine which host factors are able to counteract the viral silencing suppressors in citrus, which is related to the generation of siRNAs in response to virus infection [ 16 , 31 ]. CTV CP also acts as a silencing suppressor, and a single amino acid substitution affected symptom severity in Nicotiana benthamiana [ 32 ].…”

“…CTV strain identification was performed based on phylogenetic analysis of the CP gene sequences (~672 bp). For the phylogenetic analysis, CP gene sequences from isolates previously identified on the basis on the severity of the elicited symptomatology [31,38] were obtained from NCBI (https://www.ncbi.nlm.nih.gov/, accessed on 14 February 2022). Multiple sequence alignment (MSA) was performed using the MAFFT software version 7 [39] (https://mafft.cbrc.jp/alignment/software/, accessed on 14 February 2022), and final sequence edition was performed manually for further gap elimination with MEGA X software [40].…”

The serial and generation intervals from SARS-CoV-2 transmission dynamics and their potential application in the epidemiology of two citrus diseases

“…For example, in Mexico, the incidence of CTV diseased trees increased 40% in a period of four years. Dispersal of severe isolates is increased by A. citricidus, even in rootstocks considered tolerant to CTV (Rivas-Valencia et al, 2020).…”

“…Por ejemplo, en México, la incidencia de árboles con VTC aumentó 40% en cuatro años. La dispersión de aislamientos severos aumenta gracias a A. citricidus, incluso en patrones considerados tolerantes a VTC (Rivas-Valencia et al, 2020).…”

Nucleotide Sequence Assessment of Four ORFs of Citrus Tristeza Virus: Evidence of Recombination

“…New strains have recently been proposed, including NC (aka HA16-5), S1, L1, and M1 [25,26]. Based on CP and P18 gene sequencing, severe CTV isolates close to the T36 genotype and moderate CTV isolates similar to the T30 genotype have recently been found in eastern Mexico and Georgia state, USA, respectively [27,28]. Phylogenetic study based on four genomic ORFs (ORF1a, p25, p23, and p18) has recently allowed CTV isolates to be classified into nine broad groups: RB, T36, T30, T3, T68, VT or VT-B, HA16-5, B1, and B2 [22].…”