Studies on Citrus tristeza virus in Iran
In Iran, citrus production covers 250,000 ha and the major citrus-growing regions are located in the north along the Caspian Sea (e.g. Mazandaran province) and in several provinces in the south (e.g. Fars province). Sweet oranges (Citrus sinensis), mandarins (C. reticulata) and Mexican lime (C. aurantifolia) are the main citrus species grown. Citrus tristeza virus (Closterovirus – CTV, EPPO A2 list) was first recorded in the north of Iran in 1977. It is hypothetized that CTV was massively introduced into Iran via imports of Satsuma mandarins (C. unshiu) on trifoliate orange rootstocks (Poncirus trifoliata) from Japan in the late 1960s. For several years, CTV remained confined to northern Iran until its recent spread by Aphis gossypii to southern Iran where it was detected in 1996. 22 isolates of CTV were collected from the Mazandaran (north) and Fars (south) provinces and were characterized (ELISA, RT-PCR, RFLP, comparison of CP gene sequences). All isolates were collected from citrus trees showing various CTV symptoms (e.g. decline for trees grafted on sour orange, inverse pitting below bud union on some sour orange rootstocks, mild to moderate stem pitting on the trunks of some sweet orange trees). No major differences could be observed between isolates collected from the north and the south of Iran. It was found that Iranian isolates showed high similarity with severe strains from California and Japan. It was concluded that these severe strains could represent a threat to the citrus industry, as natural spread of CTV is occurring and sour orange is still widely used as a rootstock. It was also considered that more extensive surveys should be done to better analyse CTV populations occurring in Iran.
Sources
Barzegar A, Sohi HH, Rahimian H (2005) Comparative sequence analysis of coat protein gene of Iranian Citrus tristeza virus isolates. Journal of Phytopathology 153(7-8), 457-463.