Tomato yellow leaf curl virus (TYLCV) poses a serious threat to tomato production throughout the temperate regions of the world. A new analysis suggests that the virus probably arose somewhere in the Middle East between the 1930s and 1950s and that its global spread only began in the 1980s after the emergence of two strains – TYLCV-Mld and -IL. In agreement with other work, it finds that the highly invasive TYLCV-IL strain has jumped at least twice to the Americas – once from the Mediterranean basin in the early 1990s and once from Asia in the early 2000s. Although the results corroborate historical accounts of TYLCV-like symptoms in tomato crops in the Jordan Valley in the late 1920s, they indicate that the region around Iran is both the current center of TYLCV diversity and is the site where the most intensive ongoing TYLCV evolution is taking place. The analysis indicates that this region is epidemiologically isolated suggesting that novel TYLCV variants found there are probably not direct global threats, and identifies the Mediterranean basin as the main launch-pad of global TYLCV movements.
The Spread of Tomato Yellow Leaf Curl Virus from the Middle East to the World. (2010) PLoS Pathog 6(10): e1001164. doi:10.1371/journal.ppat.1001164
The ongoing global spread of Tomato yellow leaf curl virus (TYLCV; Genus Begomovirus, Family Geminiviridae) represents a serious looming threat to tomato production in all temperate parts of the world. Whereas determining where and when TYLCV movements have occurred could help curtail its spread and prevent future movements of related viruses, determining the consequences of past TYLCV movements could reveal the ecological and economic risks associated with similar viral invasions. Towards this end we applied Bayesian phylogeographic inference and recombination analyses to available TYLCV sequences (including those of 15 new Iranian full TYLCV genomes) and reconstructed a plausible history of TYLCV’s diversification and movements throughout the world. In agreement with historical accounts, our results suggest that the first TYLCVs most probably arose somewhere in the Middle East between the 1930s and 1950s (with 95% highest probability density intervals 1905–1972) and that the global spread of TYLCV only began in the 1980s after the evolution of the TYLCV-Mld and -IL strains. Despite the global distribution of TYLCV we found no convincing evidence anywhere other than the Middle East and the Western Mediterranean of epidemiologically relevant TYLCV variants arising through recombination. Although the region around Iran is both the center of present day TYLCV diversity and the site of the most intensive ongoing TYLCV evolution, the evidence indicates that the region is epidemiologically isolated, which suggests that novel TYLCV variants found there are probably not direct global threats. We instead identify the Mediterranean basin as the main launch-pad of global TYLCV movements.