Molecular epidemiology of Tomato yellow leaf curl disease complex infecting tomato in Oman

Tomato yellow leaf curl disease (TYLCD) is the most serious viral disease of tomato crops in Oman. The causal agent responsible to poor fruit yield is Tomato yellow leaf curl virus (TYLCV) accompanied by DNA satellites (betasatellite and alphasatellite). TYLCV was detected for the first time in 2008 in tomato crops in the Sultanate of Oman and its infestation has increased since its first detection. The infected tomato plants exhibit severe growth stunting, reduced leaflet size, upward and/or downward leaf cupping and interveinal chlorosis. Although these symptoms were observed more than two decades ago, however it never got full attention. In order to avoid the huge losses due to TYLCV, growers introduced resistant and/or tolerant tomato genotypes but the rapid recombination has led to resistance breaking strains. These strains cause severe symptoms and lead to severe problems in the tomato crop. As a result of recombination events, several new species including Tomato yellow leaf curl virus (TYLCV), Tomato leaf curl Oman virus (ToLCOMV), Tomato leaf curl Al-Batinah virus (ToLCABV), Tomato leaf curl Sudan virus (ToLCSDV), Chilli leaf curl virus (ChLCV) and Tomato leaf curl Barka virus (ToLCBrV) have been emerged and characterized whereas several others remained uncharacterized. The viruses have been detected mainly in tomato and pepper and might be spreading to other crops because of their polyphagous vector, Bemisia tabaci. In this endless arms race between plant and virus, there is an urgent need to survey tomato growing areas and characterize all TYLCV-like viruses. No previous studies have dissected the epidemiology of TYLCD complex in Oman; they only described different species/strains of TYLCV but apparently there are many others yet to be discovered, since the previous studies have not been expanded to diverse geographical locations. The main objective of this study is to survey the entire tomato growing regions of Oman, collect samples showing different degrees of disease severity and characterize all viral strains infecting the tomato crop. Once molecular characterization of the viruses is completed, agrobacterium-mediated infectious constructs of recombinant viral species will be produced to study virus-host interaction. Finally, for long term study whole viral sequences will be analyzed to identify the most conserved regions among all viruses and these regions will be targeted to produce pathogen based resistance through RNAi against this devastating viral complex.