Selection-driven emergence of resistance-breaking recombinant tomato yellow leaf viruses in Mediterranean countries

Tomato yellow leaf curl virus is one of the most damaging plant viruses. Following its progression from the Middle East to the Mediterranean Basin, TYLCV has spread globally during the last 30 years. TYLCV induce dramatic losses in tomato and its control requires important investments, for insecticides, the building of insectproof shelters and the selection of resistant cultivars. All resistant commercial varieties deployed in the Mediterranean Basin in the 2000s, have the Ty-1 gene with which the symptom expression is blocked. As the Ty-1 gene reduce but does not block virus multiplication, the infected plants are healthy carrier in which TYLCV was able to efficiently evolve through its propensity to recombine. Thus, in 2010, a recombinant, TYLCV-IS76, has been detected in Morocco in a few plants which exhibited TYLCV symptoms. IS76 is a recombinant between TYLCV and tomato yellow leaf curl Sardinia virus (TYLCSV), a virus endemic to the Mediterranean Basin. Surveys have shown that IS76 has replaced parental viruses in the South of Morocco and that it has spread to the whole country. IS76 was experimentally shown to be more competitive than parental viruses and particularly in Ty-1 resistant plants. As IS76 could not be detected on plants sampled before the deployment of Ty-1 varieties, its invasion has been associated with positive selection by these varieties. Similar results are presently obtained with a TYLCV/TYLCSV recombinant detected in Sicily on symptomatic resistant plants