Further Investigations on Citrus tristeza virus (CTV) in Sudan Using Molecular Techniques

The natural occurrence of Citrus tristeza clostero virus (CTV) in the main citrus producing regions of Sudan was further substantiated by using a nested RT-PCR approach. Two-thirds of the test samples collected from mandarin, sweet orange, grapefruit, and lime trees reacted positively and a fragment size of 132 bp using an internal and external primer sets were obtained. Cloning and sequencing of these fragments further confirmed the identity of the Sudanese isolates of CTV. The sequence analyses of the first group showed 97% nucleotide identity to a CTV strain from California causing severe stem pitting symptoms (AF01623). The second group was identical to the reference sequence (DSMZ PV-0332 from Israel) and showed 99% identity to CTV strains T30 and T36 from Florida (AF260651 and U 16304). Whereas the third group showed 94% identity to CTV strain T318A from Spain that causes severe stem pitting in sweet orange. The three different sequences obtained from Sudan revealed a lower nucleotide identity among them (about 97%) indicating that at least three different CTV-strains might be present in citrus growing areas of Sudan.