First Report of Tomato chlorosis virus in Lebanon

Abstract

Tomato seedlings showing leaf curl and yellowing symptoms characteristic of Tomato yellow leaf curl virus (TYLCV) were brought to the university laboratory from a commercial tomato greenhouse located in the Damour coastal area, south of Beirut, Lebanon. They were first tested using polymerase chain reaction (PCR) to ascertain their infection by TYLCV and then they were used in a trial to evaluate resistance of three local accessions of tomato to TYLCV, the major limiting factor to tomato production in Lebanon. Whiteflies (Bemisia tabaci), reared on broccoli for several generations, were allowed an acquisition access period of 48 h on tomato seedlings putatively infected with TYLCV and then were transferred to test plants at an average of 40 to 60 whiteflies per tomato seedling at the first-true leaf stage for an inoculation feeding period of 3 days. All treatments were conducted in insect-proof cages. Clear TYLCV symptoms were observed on the three local tomato accessions approximately 3 weeks after inoculation. However, 7 to 8 weeks after inoculation, many plants showed yellowing symptoms on the lower leaves that were not observed in previous experiments. Infections by Tomato chlorosis virus (ToCV) and/or Tomato infectious chlorosis virus (TICV), two criniviruses belonging to the family Closteroviridae, were suspected. Diagnostic tests using PCR for TYLCV detection (1) and reverse transcription (RT)-PCR for detection of ToCV (2) or TICV (3) showed that some tomato plants had a mixed infection with TYLCV and ToCV. None of the tested samples was positive for TICV. The RT-PCR amplicons (434 nt) obtained with the ToCV specific primers were cloned into pGEM-T easy vector. Sequence analysis of one clone revealed more than 99% nucleotide identity with the heat shock protein homologue (HSP70h) of ToCV isolates from the United States (GenBank Accession Nos. AY903448, AF024630, and AY444872) and 100% amino acid identity to ToCV isolates from Italy and Portugal (GenBank Accession Nos. AY048854.1 and AF234029.1). The sequence was submitted to GenBank (Accession No. DQ234079). Twenty-two tomato samples were then collected from plants showing yellowing symptoms on their lower leaves. The samples were taken from two greenhouses at the same farm in the Damour area. Six samples tested positive for ToCV using RT-PCR. To our knowledge, this is the first report of ToCV in Lebanon, but its incidence and distribution was not monitored. However, on the basis of symptoms and preliminary RT-PCR results, the disease does not appear to be widely spread in the country. References: (1) G. H. Anfoka et al. J. Plant Pathol. 87:65, 2005. (2) D. Louro et al. Eur. J. Plant Pathol. 106:589, 2000. (3) A. M. Vaira et al. Phytoparasitica 30:290, 2002.