Orobanche ramosa L. is a parasitic plant that affects tobacco in Europe and Asia. In France and Germany, despite ancient presence of this parasite, significant damages occurred only recently, and tobacco production became impossible in some farms. A screening of the ITB germplasm collection was conducted by ANITTA in heavily infested fields from Poitou in 2002 and 2003. Some flue-cured lines from Polish origin, more particularly the cultivar Wika, were consistently parasitized by a lower number of Orobanche shoots than other flue-cured, and these shoots appeared later in the season. Further field trials in 2004 and 2005 confirmed these results. In an attempt to understand the underlying mechanism, a test in controlled conditions was set up at ALTADIS-Bergerac. Individual tobacco plants were grown in Petri dishes filled with a synthetic substrate and added with approximately 500 Orobanche seeds. Root systems of tobacco plants, as well as Orobanche seeds and roots, could be examined periodically in a non-destructive way under binocular lenses. A much lower number of Orobanche seed germinated in Petri dishes with growing roots of the cultivar Wika than with fully susceptible checks, and this germination occurred later. However, the few germinated Orobanche seeds that could attain a tobacco root of Wika succeeded in parasitizing the plant. An F₂generation from the cross between Wika and a susceptible flue-cured line was tested in these controlled conditions. Among 120 individual plants, 25% showed the same behaviour than Wika, whereas the 75% remaining were attacked in a similar way to the susceptible parent. It was concluded that a single recessive gene is involved. Low production of germination stimulants that are required by the Orobanche seed to germinate might be the underlying mechanism.