A New Geminivirus Associated with a Leaf Curl Disease of Tomato in Tanzania

Leaf samples of tomato exhibiting yellow mottle, severe leaf curl, stunting, and upright stems were collected from Makutupora, Tanzania, in October 1994 by L. L. Black (AVRDC). Leaf tissue squashes on nylon membranes did not hybridize with DNA-A probes from tomato yellow leaf curl geminiviruses (TYLCVs) from Thailand (Thai) or Egypt (EG), an isolate of TYLCV-Isr (Israel). Polymerase chain reaction (PCR) with primer pair PAC1v1978/PAV1c715 (2), which specifically amplifies part of the rep (AC1) open reading frame (ORF), the intergenic region, and the cp (AV1) ORF of whitefly-transmitted geminiviruses, yielded a 1.5-kb fragment from a DNA extract of symptomatic tomato leaves. No virus-specific fragments were amplified from symptomless tomato leaves. The nucleotide sequence (GenBank accession no. U73478) of the PCR fragment (recombinant plasmid pAF1) was compared with the sequences of seven distinct subgroup III geminiviruses that infect tomato (1)-TYLCV-Isr, TYLCV-Sar (Sardinia), TYLCV-Thai, tomato leaf curl virus (TLCV)-;Aus (Australia), IndTLCV (India), TLCV-Ind (Bangalore I), and TLCV-Tai (Taiwan)-as well as three other subgroup III geminiviruses from the Old World: Indian cassava mosaic virus, African cassava mosaic virus, and mung bean yellow mosaic virus. Nucleotide sequence identities for the pairwise comparisons of the rep ORF (692 nucleotides) and the intergenic region (169 nucleotides) of this Tanzanian geminivirus with those of the 10 Old World geminiviruses showed low nucleotide identities, which were <79% for the rep ORF and <67% for the intergenic region. Since isolates of the same geminivirus usually have nucleotide sequence identities >90% (1), this Tanzanian geminivirus is considered to be different from all previously characterized Old World geminiviruses and is given the name TLCV-Tan. Further, tissue squash blots of samples previously collected from other areas in Tanzania gave strong positive reactions with the TYLCV-EG probe, so yet another geminivirus closely related to TYLCV-Isr may be present. References: (1) M. Padidam et al. J. Gen. Virol. 76:249, 1995. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.