In Jordan, as well as many countries in the region, tomato production is threatened by begomoviruses belonging to the tomato yellow leaf curl virus complex (1). In 2013, an experiment was conducted at Homret Al-Sahen, Jordan (GPS coordinates 32°05′06″ N, 35°38′52″ E), to evaluate different tomato breeding lines for resistance against viruses causing tomato yellow leaf curl disease (TYLCD). Disease symptoms, typical of those caused by TYLCV complex, were observed in many susceptible lines. However, some lines exhibited unusual symptoms including severe leaf curling and stunting. To identify the causal agent of these symptoms, total nucleic acids were extracted from 21 symptomatic plants and used as templates in PCR analysis using nine primers, previously described to detect Tomato yellow leaf curl virus, Tomato yellow leaf curl Sardinia virus, and two recombinants between TYLCV and TYLCSV (3). In addition, the universal primer pair β01/β02 (2) was used to investigate the association of satDNA β with the disease. The PCR products characteristic of TYLCV (664 bp) could be amplified from five plants indicating single infection, while double infection with TYLCV and satDNA β (1,320 bp) was detected in seven plants. Mixed infection with TYLCV, TYLCSV (628 bp), and satDNA β was detected in another seven symptomatic plants and only one plant was infected with TYLCV and TYLCSV. A single plant had mixed infection with TYLCV, TYLCSV, and RecA (a recombinant between TYLCV/TYLCSV) (538 bp) (3). Amplicons obtained from two plants using β01/β02 primers were directly sequenced as 1,320-bp PCR products. Both sequences were found identical and, therefore, this sequence was deposited in the GenBank under the accession number KJ396939. Phylogenetic analysis revealed that this satDNA β sequence had the highest nucleotide (95%) identity with Okra leaf curl virus (OkLCV) satDNA 3 (AF397217) and OkLCV satDNA 10 (AF397215). The contribution of the satDNA β in the modulation of the TYLCD symptoms will be further investigated. Few years ago, another satDNA (Tomβ01-Om) was reported in Oman to be associated with TYLCD (4). However, to the best of our knowledge, this is the first report on the detection of satDNA β in tomato plants infected with viruses causing TYLCD in Jordan. The increasing diversity of begomoviruses causing TYLCD in the region is of great concern due to the possible emergence of more virulent viruses and subsequent increased losses to tomato production.
References: (1) G. Anfoka et al. J. Plant Pathol. 90:311, 2008. (2) R. W. Briddon and J. Stanley. Virology 344:198, 2006. (3) S. Davino et al. Virus Res. 143:15, 2009. (4) A. J. Khan et al. Virus Gene 36:169, 2008.