Characterization of Citrus tristeza virus Isolates by Indicators and Molecular Biology Methods

Citrus tristeza virus (CTV) exists in citrus as a large number of distinct strains differing in biological characters. The control strategies such as mild strains cross protection (MSCP) require a clear understanding of the characterization of CTV. For better understanding of the structure of CTV population and the relationship between molecular and biological characterization, 72 CTV samples collected from five provinces in China were studied, using biological indexing, p25/Hinf I restriction fragment length polymorphism (RFLP), multiple molecular markers, and bidirectional RT-PCR assay. The mixture of severe stem pitting isolates was found to be dominant in the field. CTV isolates with p25/Hinf I RFLP group 3 and p23/BD-PCR group I, 111 were the main cause of epidemics, and most CTV isolates were found to be the mixture of T30 and VT genotypes. More accurate identification of strain mixtures in the field and better understanding of the biological traits of the isolates may be achieved by applying the three molecular detection methods simultaneously.