The occurrence of innumerable pests and diseases associates to the plantation in not irrigated areas is some of the factors that explain low the productivity of the culture of citrus in São Paulo. Among the diseases, are distinguished clorose variegada of the citros (CVC), citrus canker, leprosis, sudden death and more recently huanglongbing (ex-greening), considered most serious and destructive of diseases of citrus and caused by the Gram-negative bacterium limited to the floem – Candidatus Liberibacter spp. This disease is know in Asia and Africa at long time, however it was related officially in Brazil (Araraquara-SP) in July of 2004 and 2005 in the Flórida – U.S.A.. The bacterium can be transmitted through contaminated vegetal material (buds), or through vector (Diaphorina citri), or still experimentally for Cuscuta campestris. In the plants of citros, the presence of the bacterium results in symptoms many times confused with nutritional problems. All the crown varieties of sweet orange, mandarins and hybrids Inter or intra-specific of the Citrus genus are susceptible. Bringing to extend the genomics knowledge about bacterium (once that the current available information restrict it few ribossomic genes) and to the HLB pathosystem, the objectives this work is: 1. sequencing genomics regions of Candidatus Liberibacter spp; 2. to evaluate through ‘microarrays’ distinguishing express genes in plants of sweet orange infecteds or not with the bacterium; 3. to validate, for RT-qPCR, the set of genes that more could be associates to the reply of the plant to the infection.
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