Studies on Citrus tristeza virus Egyptian isolates
Isolates of Citrus tristeza virus (Closterovirus, CTV – EPPO A2 list) differ in their biological characteristics and particularly in the severity of symptoms they produce on citrus species and cultivars. In Egypt, CTV does not cause a major disease on citrus, although the majority of orchards are planted with sweet oranges (Citrus sinensis) grafted on sour orange rootstocks (C. aurantium). The aphid vector, Aphis gossypii, occurs in Egypt but to date, its most efficient vector, Toxoptera citricidus, has never been found. Three Egyptian isolates of CTV were collected at 2 locations from rough lemon trees (C. jambhiri) grafted on sour orange, showing symptoms of decline. The capsid protein gene was amplified by RT-PCR, and analysed by SSCP (single stranded conformation polymorphism) and sequencing. Comparison with reference sequences (of isolates coming from other parts of the world) showed that the Egyptian isolates were very similar to a severe strain from Florida which causes quick decline and stem pitting. These results suggested that isolates causing severe quick decline are present in Egypt, although tristeza epidemics have not yet been observed in the country.
Sources
Amin HA, Fonseca, F, Santos C, Nolasco G (2006) Typing of Egyptian Citrus tristeza virus (CTV) isolates based on the capsid protein gene. Phytopathologia Mediterranea 45(1), 10-14.