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We report the complete nucleotide sequence of DNA-A of a begomovirus naturally infecting Jatropha curcas L. in Nigeria. Symptoms observed on infected plants were severe mosaic, mottling and blistering of leaves. The virus, which we provisionally name "jatropha mosaic Nigeria virus" (JMNV), has a monopartite genome of 2,779 to 2,789 nucleotides. Pairwise comparisons of DNA-A sequences showed that JMNV had maximum nucleotide sequence identity (72%) with a strain of tomato yellow leaf curl virus. Since there are widespread infections of jatropha in Nigeria showing similar symptoms as those investigated in the present study, JMNV may represent a significant threat to a promising bioenergy crop.

Tomato samples with typical symptoms of tomato yellow leaf curl virus (TYLCV) infection were collected from six tomato growing regions in Tanzania and dot-blotted on nylon membranes. The membranes were hybridised with nucleic acid probes synthesized to detect TYLCV from Israel and Sardinia. Viral DNA was extracted from the samples by phenol-chloform procedure and amplified by polymerase chain reaction using a primer pair (OTY 2 and OTY 6) designed to amplify a 1.2 kb fragment containing the coat protein, intergenic region and replicationassociated protein. The amplified DNA was ligated to pBluescript II KS + and transformed into Esherichia coli strain JM 83 cells by electroporation. Colonies containing the insert were sequenced using a Li-Cor DNA Semi-automatic Sequencer. The BLAST programme was used to search for viruses with similar sequences. Phylogenetic relationships with 20 geminiviruses were established using the CLUSTAL function of the Vector NT1.5 software. Amplified DNA was digested with Alu I and electrophoresed in polyacrylamide gel. Tomato yellow leaf curl virus samples from all the regions hybridised with both probes. Restriction analysis showed similar banding patterns for all the isolates. Both sequence comparison and phylogeny showed that TYLCV from Tanzania was closely related to TYLCV-Sar. The TYLCV isolates from the six regions were genetically the same.

A survey was initiated to detect tomato yellow leaf curl virus (TYLCV) and identify its reservoir weed hosts in six regions (Arusha, Morogoro, Dodoma, Iringa, Kilimanjaro and Dar es Salaam) in Tanzania. Three farms were randomly selected in each region. Assessment of TYLCV incidence was done by relating the number of infected tomato plants to the total number of plants assessed along a diagonal in five quadrants measuring 4 m × 4 m in size (one at each corner of the farm and one at the centre). Disease severity was scored on a scale of 0 to 4 (where 0 = no symptoms and 4 = very severe symptoms). Within and outside each farm, weeds showing TYLCV-like symptoms were collected and either squash-blotted, dot-blotted or both on nylon membranes. The membranes were hybridized with DIG-labelled probe synthesized for the detection of TYLCV from Sardinia (TYLCV-Sar) following standard protocols. Selected plant species were experimentally inoculated with screenhouse cultures of TYLCV representative isolates from the six regions using Bemisia tabaci to determine their host status. Results indicated that TYLCV incidence and severity were significantly higher (P = 0.05) in Dodoma region than the rest of the regions. In Iringa region, the incidence and severity of TYLCV were the lowest of all regions. TYLCV was detected in 12 of the 17 dot-blotted samples and in all the 21 squashed samples using the non-radioactively labelled riboprobes. Similarly, five plant species (Capsicum annuum, Datura stramonium, Lycopersicon esculentum, Nicotiana glutionsa and N. tabacum) tested in the screenhouse were infected by the six TYLCV isolates used. It is recommended that weeds within and outside tomato farms be removed to eliminate or reduce sources of virus inoculum. The dot and squash blot techniques are convenient for field detection of the virus, and are especially useful for the detection of early and latent infections so that management strategies can be initiated and implemented.

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