Molecular Characterization of a New Tomato Begomovirus from India.

Abstract

The Asian Vegetable Research and Development Center's (AVRDC) tomato breeding lines derived from Lycopersicon hirsutum f. glabratum B 6013 × L. esculentum H-24 and carrying the Ty-2 resistance gene located on chromosome 11 are tolerant to tomato leaf curl disease in Karnataka State, southern India (3), where several isolates of Tomato leaf curl Virus-Bangalore (GenBank Accession Nos. L11746, Z48182, and AF165098) and Tomato leaf curl virus-Karnataka (GenBank Accession No. U38239) are reported to infect tomatoes. The only area in south and southeast Asia where these AVRDC tomato breeding lines were found susceptible to begomovirus infection is Thailand, where several bipartite Tomato yellow leaf curl virus isolates (GenBank Accession Nos. X63015, X63016; AF141922, AF141897; and AF511529, AF511528) are reported to be prevalent. However, in field trials conducted in the fall of 1999 in Bodeli, Gujarat State, western India, the AVRDC breeding lines showed typical symptoms of begomovirus infection, such as leaf curling and vein clearing. The presence of a different tomato begomovirus was suspected. Viral DNA from a symptomatic plant from Bodeli was amplified by polymerase chain reaction (PCR) using the begomovirus-specific degenerate primer pair PAL1v1978/PAR1c715 (4) and the expected 1.4-kb PCR product was obtained. Based on the sequence of the 1.4-kb DNA product, specific primers were designed to complete the DNA-A sequence. The DNA-A of the virus associated with tomato leaf curl from Bodeli consists of 2,759 nucleotides (GenBank Accession No. AF413671) and contains six open reading frames (ORFs V1, V2, C1, C2, C3, and C4). The DNA-A sequence of the Bodeli isolate had highest sequence identities of 98 and 98.3%, respectively, with viruses causing tomato leaf curl from Varanasi, Uttar Pradesh State, northern India (GenBank Accession No. AF449999) collected in the fall of 1999 and Panchkhal, Nepal (GenBank Accession No. AY234383) collected in early 2000. There was no evidence for the presence of DNA-B in the Bodeli, Panchkhal, or Varanasi virus isolates using DNA-B specific primer pairs DNABLC1/DNABLV2 and DNABLC2/DNABLV2 (2). However, a 1.3-kb DNA-beta was detected in the Panchkhal and Varanasi isolates using the primer pair Beta01/Beta02 (1). Sequence comparisons with begomovirus sequences available in the GenBank database showed that these three virus isolates and GenBank Accession No. AY190290 collected in 2001 from Varanasi shared more than 97% sequence identity with each other and should be considered closely related strains of the same virus. These four virus isolates belong to a new distinct tomato geminivirus species because their sequences share less than 88% sequence identities with the next most closely related virus, Tomato leaf curl virus-Karnataka (GenBank Accession No. U38239). This new tomato leaf curl virus is prevalent in western India, northern India, and Nepal.