Search

Tomato yellow leaf curl virus-Oman (TYLCV-OM),  a variant of the Tomato yellow leaf curl virus-Iran (TYLCV-IR) strain, was identified in 2005 as the cause of tomato yellow leaf curl disease (TYLCD) in Oman and is  associated with a betasatellite namely as Tomato leaf curl betasatellite (ToLCB). Surveys were carried out from three diverse Governorates of Oman to investigate the correlation between the betasatellite and the virus. The visual assessment and scoring of infected tomato plants in the field revealed that the association of betasatellite with the disease was highest in Sharqia at 77%, followed by Dakhlia at41% and lowest in Batinah at30% . Ten isolates from three distinct regions of Oman were analyzed: two from Al Batinah, two from A'Dakhliah, and six from A'Sharquiah. All TYLCV-OM isolates were identified as variants of the 2005 isolates Al Batinah. However, a new recombinant form of TYLCV-OM, which could impact its virulence or spread, was identified in the Al Batinah region. Mutations observed in the Al Batinah isolates of TYLCV-OM coincided with recombination events involving ToLCOMV. Examination of the intergenic regions (IRs) of TYLCV-OM and ToLCOMV indicated that recombination occurred within the IR. Specifically, TYLCV-OM acquired a segment spanning coordinates 1 to 132 nt from ToLCOMV, which may influence its genetic diversity. The implications of these findings for the evolutionary dynamics of the begomovirus complex associated with yellow leaf curl disease are discussed. Inoculation of infectious construct of TYLCV-OM alone or with ToLCB resulted in severe leaf curl symptoms but leaf yellowing was more pronounced in the presence of ToLCB. Real-time quantitative data showed that TYLCV-OM was accumulated to higher level in the presence of betasatellite.

Background: Tomato yellow leaf curl virus (TYLCV), a monopartite begomovirus (family Geminiviridae) is responsible for heavy yield losses for tomato production around the globe. In Oman at least five distinct begomoviruses cause disease in tomato, including TYLCV. Unusually, TYLCV infections in Oman are sometimes associated with a betasatellite (Tomato leaf curl betasatellite [ToLCB]; a symptom modulating satellite). RNA interference (RNAi) can be used to develop resistance against begomoviruses at either the transcriptional or post-transcriptional levels., Results: A hairpin RNAi (hpRNAi) construct to express double-stranded RNA homologous to sequences of the intergenic region, coat protein gene, V2 gene and replication-associated gene of Tomato yellow leaf curl virus-Oman (TYLCV-OM) was produced. Initially, transient expression of the hpRNAi construct at the site of virus inoculation was shown to reduce the number of plants developing symptoms when inoculated with either TYLCV-OM or TYLCV-OM with ToLCB-OM to Nicotiana benthamiana or tomato. Solanum lycopersicum L. cv. Pusa Ruby was transformed with the hpRNAi construct and nine confirmed transgenic lines were obtained and challenged with TYLCV-OM and ToLCB-OM by Agrobacterium-mediated inoculation. For all but one line, for which all plants remained symptomless, inoculation with TYLCV-OM led to a proportion (≤25%) of tomato plants developing symptoms of infection. For inoculation with TYLCV-OM and ToLCB-OM all lines showed a proportion of plants (≤45%) symptomatic. However, for all infected transgenic plants the symptoms were milder and virus titre in plants was lower than in infected non-transgenic tomato plants., Conclusions: These results show that RNAi can be used to develop resistance against geminiviruses in tomato. The resistance in this case is not immunity but does reduce the severity of infections and virus titer. Also, the betasatellite may compromise resistance, increasing the proportion of plants which ultimately show symptoms.