Citrus leprosis, caused by Citrus leprosis virus C (CiLV-C), is currently considered the most important viral disease in the Brazilian citrus industry due to the high costs required for the chemical control of its vector, the mite Brevipalpus phoenicis. The pathogen induces a non-systemic infection and the disease is characterized by the appearance of localized lesions on citrus leaves, stems and fruits, premature fruit and leaf drop and dieback of stems. Attempts were made to promote in vitro expression of the putative cell-to-cell movement protein of CiLV-C in Escherichia coli and to produce a specific polyclonal antibody against this protein as a tool to investigate the virus-plant-vector relationship. The antibody reacted strongly with the homologous protein expressed in vitro by ELISA, but poorly with the native protein present in leaf lesion extracts from sweet orange caused by CiLV-C. Reactions from old lesions were more intense than those from young lesions. Western blot and in situ immunolocalization assays failed to detect the native protein. These results suggest low expression of the movement protein (MP) in host tissues. Moreover, it is possible that the conformation of the protein expressed in vitro and used to produce the antibody differs from that of the native MP, hindering a full recognition of the latter.

Plants not only evolve but also reduce oxygen in photosynthesis. An inevitable consequence of this normal process is the production of reactive oxygen species (ROS). Plants are adequately protected by the presence of multiple antioxidative enzymes in the cytosol and also in the different cell organelles such as chloroplasts, mitochondria, and peroxisomes. Traditionally, ROS were considered to be only a toxic byproduct of aerobic metabolism. However, recently it has become apparent that plants actively produce these molecules which may control many different physiological processes such as abiotic and biotic stress response, pathogen defense and systemic signaling. The search results using the Citrus Genome Program in Brazil (CitEST) for oxidative stress and the antioxidant enzyme system in Citrus Sinensis variety ‘Pera IAC’ indicated that the multiple ROS-scavenging enzymes were expressed throughout all citrus tissues. The analyses demonstrated the ubiquitous expression of metallothioneins, probably indicating a constitutive expression pattern. Oxalate oxidase has been identified as the most abundant expressed gene in developing fruits, which suggests a specific function in the ripening of citrus fruit. Moreover, infected leaves with Xylella fastidiosa and Leprosis citri showed a massive change in their ROS gene expression profile which may indicate that the suppression of ROS detoxifying mechanisms may be involved in the induction of the diseases.

Isolados do vírus da tristeza dos citros (CTV) de 35 acessos de pomelos que fazem parte do Banco Ativo de Germoplasma de Citros, localizado no Centro APTA Citros Sylvio Moreira, Cordeirópolis, São Paulo, Brasil, pertencente ao Instituto Agronômico de Campinas (IAC), foram caracterizados através dos sintomas observados nas árvores, indexação biológica, diagnóstico imunológico e análise SSCP (polimorfismo de conformação de fita simples) do gene da proteína do capsídeo. O grupo de plantas que, em geral, apresentou menor volume de copa e severo sintoma de canelura diferenciou-se significativamente do grupo com maior desenvolvimento vegetativo e fraco a moderado sintoma de canelura. No entanto, a maioria dos isolados de CTV das plantas de ambos os grupos induziu fraca reação em limão galego e nenhuma relação entre títulos do vírus nos tecidos e sintomatologia foi observada na avaliação sorológica conduzida por DAS-ELISA. A reação com diferentes anticorpos monoclonais e os distintos padrões eletroforéticos obtidos por SSCP demonstraram que há uma grande diversidade entre os isolados de CTV que infectam os acessos de pomelos. Alta complexidade de bandas dentro de um mesmo isolado foi também observada nos perfis SSCP, demonstrando que cada isolado é constituído por uma mistura de diferentes haplótipos de CTV. Padrões SSCP semelhantes foram observados entre algumas plantas com fortes sintomas de caneluras e entre algumas plantas com sintomas fracos ou moderados de caneluras.

Citrus tristeza virus (CTV) isolates from 35 grapefruit accessions belonging to Citrus Active Germplasm Bank of the "Instituto Agronômico de Campinas" located at the "Centro APTA Citros Sylvio Moreira", Cordeirópolis, São Paulo state, Brazil, were characterized and evaluated through symptoms in the trees, biological indexing, immunological diagnosis with different monoclonal antibodies and SSCP analysis (single-strand conformation polymorphism) of the coat protein gene. Symptomatology indicated that, in general, the group of plants with smaller canopy volume and severe stem pitting differed significantly from the group that presented greater vegetative development and mild to moderate stem pitting. However, the isolates from most of the accessions induced mild reaction on Mexican lime. The serological evaluation through the DAS-ELISA using monoclonal antibodies did not reveal any association between virus titer in the plant tissue and symptoms. The reaction with different monoclonal antibodies and the distinct electrophoresis patterns obtained through SSCP showed that there is a high degree of diversity among the isolates that infect these grapefruit accessions. High complexity within the same isolate was also observed in the SSCP profiles. This finding indicates that the CTV isolates from these plants are a complex mixture of CTV haplotypes. Similar SSCP banding patterns were observed among some plants with strong stem pitting symptoms, and among some plants with weak or moderate stem pitting symptoms.