Since 1988, viroids have been occasionally detected in samples of tomato (Lycopersicon esculentum) originating both in the Netherlands and other countries. Infected plants showed chlorosis, bronzing, leaf distortion and growth reduction. Initial diagnosis of these viroids was by return-polyacrylamide gel electrophoresis, which did not allow a further identification. This paper reports the identification of these viroids by reverse transcription-polymerase chain reaction and sequence analysis. Three known viroids of tomato, i.e. Citrus exocortis viroid; Potato spindle tuber viroid and Tomato chlorotic dwarf viroid were identified. In addition, six isolates were identified as Columnea latent viroid, a viroid so far only detected in some ornamental species. Like the isolates previously isolated from ornamental species, the isolates from tomato share genetic characteristics of both the genera Hostuviroid and Pospiviroid. The biological characteristics of all four viroids, especially their potential effects on both potato (Solanum tuberosum) and tomato, stress the need for reconsideration of their phytosanitary risks.

In 2002, a breeding company submitted several samples of tomato (Lycopersicon esculentum) for diagnosis. Samples originated in Indonesia and were taken from protected and nonprotected crops. Plants exhibited severe chlorosis on fully expanded leaves, while young leaves were symptomless. Symptoms resembled those of the criniviruses Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV). Moreover, large numbers of whiteflies, potential vectors of these viruses, had been observed at the plots with symptomatic plants. A reverse transcription-polymerase chain reaction (RT-PCR) with specific primers for TICV (1) yielded amplicons of the expected size of approximately 500 bp for all samples. One of the amplicons was sequenced (Genbank Accession No. AY221097) and revealed more than 98.9% identity to six isolates of TICV in NCBI Genbank. cDNA synthesis using the universal crinivirus primer HSP_M2-DW (5′ -TCRAARGTWCCKCCNCCRAA-3′) followed by PCR with a ToCV specific primerset (ToCV-UP 5′-TCATTAAAACTCAATGGGACCGAG-3′ and ToCV-DW 5′-GCGACGT AAATTGAAACCC-3′) was negative in all cases. Grafting of symptomatic shoots onto healthy tomato seedlings of cv. Money-maker showed transmission of the virus, as chlorosis appeared on fully expanded leaves of lateral shoots after 6 weeks. The presence of TICV in the graft-inoculated plants was confirmed by RT-PCR. Furthermore, mechanical inoculation to a range of herbaceous test plants did not evoke any virus symptoms, indicating the absence of mechanically transmissible viruses. Although other nonmechanically transmissible viruses cannot be fully excluded, the results together with the symptoms observed, indicate that TICV is the cause of the disease. TICV has been reported from Greece, Italy, Japan, Spain, and the United States, but to our knowledge, this is the first report of TICV in Indonesia. Reference: (1) A. M. Vaira et al. Phytoparasitica 30:290, 2002.

In 2000, a breeding company submitted a tomato (Lycopersicon esculentum) sample from Guatemala for diagnosis. The plants showed necrotic lesions on leaves surrounded by some chlorosis, necrotic streaks on stems, and large superficial necrotic lesions on fruits. By mechanical inoculation of plant sap to different plant species, symptoms appeared in Capsicum annuum ‘Westlandse Grote Zoete’, Lycopersicon esculentum ‘Money-maker’, Nicotiana benthamiana, N. bigelovii, N. glutinosa, N. hesperis-67A, N. occidentalis-P1, N. tabacum ‘White Burley’, and Physalis floridana. Systemically infected leaves from N. occidentalis-P1 were used for all further experiments. Leaf dip preparations were analyzed by transmission electron microscopy and revealed the presence of filamentous virus particles typical of a potyvirus. Double-antibody sandwich enzyme-linked immunosorbent assay tests for Potato virus A, V, and Y, Tobacco etch virus, and Wild potato mosaic virus were negative. An antiserum (PepMoV/DSMZ As 0186) to Pepper mottle virus (PepMoV), however, gave a positive reaction. To obtain further evidence for the presence of this virus, the nucleotide sequence of the complete 3′ nontranslated region (3NTR) and the 3′ terminal part of the coat protein gene (3CPG) was determined using the set of degenerate primers P9502/CPUP (1). The obtained nucleotide sequence (approximately 700 bp) was deposited in GenBank under Accession No. AF440801. It showed 93 to 94% 3NTR and 90 to 93% 3CPG homology with the three sequences of PepMoV from pepper already present in GenBank. The two viruses with the next closest nucleotide sequence homology were Potato virus V and Potato virus Y showing up to 80 and 75% homology with the 3CPG and up to 53 and 48% homology with the 3NTR, respectively. Based on these results, we concluded that the virus isolated from the symptomatic tomato plants was PepMoV. Because of the relatively low homologies with the pepper isolates of PepMoV, this tomato isolate might be a separate strain of the virus. To our knowledge, this is the first report of the occurrence of PepMoV in tomato. Reference: (1) R. A. A. van der Vlugt et al. Phytopathology 89:148, 1999.