Cross protection against severe isolates of citrus tristeza virus on sweet orange (Citrus sinensis L. Osb. cv. pera)

Abstract

Cross protection against severe isolates of citrus tristeza virus on sweet orange (Citrus sinensis L. Osb. cv. pera). The citrus tristeza virus (CTV) and its vector, the brown citrus aphid (Toxopetera citricida), are endemic in Brazil, and both play an important role in the low productive of the citrus orchards. The Brazilian citrus industry lives very well together with many weak or mild strains of CTV, as a result of cross protection program using protective strains in tolerant varieties of sweet oranges and rootstocks. However, such approach has not reduced the spreading of very severe strains, like the complex CTV of Capão Bonito (CB), that affect the more used rootstock in brazil, the rangpur lime (Citrus limonia). Although cross protection in the brazilian citrus industry could be considered a very successful approach in controlling severe strains of CTV, its biological and molecular bases are unknown. Protective strains of CTV have been mainly used in varieties of sweet oranges with low tolerance to the virus, allowing their use as commercial varieties, like the sweet orange pera IAC, with more than 50 millions plants in the state of São Paulo. Aiming to obtain new protective isolates of CTV for using in sweet orange pera this project supported by fapesp has the following goals: study of virus genome of protective isolates by analysis of dsRNA (double strand RNA), RFLP (restriction fragment length polymorphism), SSCP (single strand conformation polymorphism), and sequencing of several orfs (P18, P25, P27). Studies of expression, competition and challenge between strains are been carried out using sweet orange pera as a model. (AU)