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

The research work covered the in vitro establishment of Persian lime nodal segments using a twig disinfection protocol, and their culture on Murashige and Skoog (MS) culture media supplemented with antibiotics (Estrepto-Ler® and Rifampicin) and fungicide (Chlorothalonil). The axillary buds production was performed cultured the nodal segments without contamination signs on MS culture media enriched with two cytokinins (6-BAP and Kinetin) at different concentrations. Results showed that 52 % of the nodal segments did not show signs of in vitro contamination when the twig submerged in 20% chlorine for 15 min during disinfection process and nodal segments were grown in MS culture medium supplemented with 2 mg L-1 of Rifampicin and fungicide Chlorothalonil. Interestingly, MS culture medium enriched with 6-BAP (0.5 mg L-1) + Kinetin (0.5 mg L-1) turned out to be the best combination to achieve that 78 % of nodal segments promoted 1 to 2 axillary buds.

<p>Las bacterias causantes del huanglongbing (HLB), <em>Canditatus</em> Liberibacter spp., son bacterias obligadas al floema de los cítricos y a diferentes sistemas del insecto vector,<em> Diaphorina citri</em>, por lo tanto, el enfoque genómico ha sido útil para estudiar sus mecanismos de patogenicidad. Dicho enfoque ha permitido identificar una copia homóloga del gen codificante de la enzima ATP/ADP translocasa, la cual tiene la capacidad de importar ATP y nucleótidos desde el hospedante, causando un parasitismo de energía considerable. Esta enzima se ha relacionado con la actividad endoparasítica de patógenos animales y humanos más que con fitopatógenos. El presente trabajo analizó la relación evolutiva entre la secuencia de aminoácidos de la ATP/ADP translocasa entre diferentes especies de <em>Ca</em>. Liberibacter y grupos como <em>Ricketssia</em> sp. y <em>Chlamydia</em> sp. Análisis filogenéticos muestran que la variación en la secuencia del gen codificante de la enzima está delimitada en clados correspondientes a las especies de <em>Ca</em>. Liberibacter, sugiriendo que la variación en la enzima responde a un proceso coevolutivo con los hospederos. Asimismo, la filogenia muestra que el ancestro común más cercano a <em>Ca</em>. Liberibacter podría ser un endosimbionte no patogénico del género <em>Ca</em>. Midichloria. Análisis de conservación de la secuencia de aminoácidos muestran que existen varias posiciones en la secuencia que podrían estar relacionadas con la variación específica de esta enzima dentro de <em>Ca</em>. Liberibacter. Este trabajo presenta la hipótesis de que el origen evolutivo de la capacidad de parasitismo energético del género <em>Ca</em>. Liberibacter, causantes del HLB, es un endosimbionte no patogénico.</p>

Huanglongbing (HLB) or citrus greening is currently the most important citrus disease, caused by the bacterium Candidatus Liberibacter asiaticus (CLas). The impossibility of isolating it causes understanding its pathogenic mechanisms to be a complicated task. Recent studies identified 16 proteins with the signal peptide needed to be secreted in the plant and cause the disease. The present study aims to perform a bioinformatic analysis of these proteins with the function prediction approach by gene ontology (GO) and the detection of conserved domains. It was observed that of the 16 proteins analyzed not all are found in different infective strains reported in the literature. The GO analysis allowed us to relate different proteins with the biological process of energy and pathogenic activity, especially CLIBASIA_03315 and CLIBASIA_05115, respectively. The domain analysis allowed the observation of a β-CA domain, tentatively related to the damage caused to the chloroplast and a PAAR domain associated with the T6SS secretory system. Our results provide information on the possible function of potential pathogenicity effectors in CLas.

Persian lime (PL) is one of the most economically important citrus crops in the state of Veracruz, Mexico. However, it is affected by the presence of Huanglongbing (HLB) disease, caused by Candidatus Liberibacter asiaticus (CLas), an obligate biotrophic pathogen. Overall, PL shows a certain level of tolerance to HLB. Therefore, it is important to study the defense response mediated by salicylic acid (SA) against biotrophic pathogens in PL. Some genes with the capacity to participate in the SA response pathway, known as NtSABP, have been identified in Nicotiana tabacum, but the presence and activity of these genes in PL in response to HLB are unknown. The objective of this study was to identify homologues of SABP-like proteins in the PL transcriptome and to determine their differential expression level during CLas infection. SABP protein sequences from five different species, including N. tabacum, were used as model sequences in a tBLASTn search. A 3D model of the SABP protein was constructed and compared between N. tabacum and C. latifolia. We identified the direct homologous to each NtSABP gene in the PL using tBLASTn analysis, phylogenetic reconstruction, and tridimensional structure. Interestingly, the ClSABP1, ClSABP2, and ClSABP3 genes showed repression in CLas infected plants. There is at least one homologous to each NtSABP gene in PL. During CLas infection, these genes are somewhat suppressed.