Stability factors of rhizomania resistance in sugar beet

Rhizomania in sugar beet is caused by the Beet necrotic yellow vein virus (BNYVV) and transmitted by the soil-borne plasmodiophoromycete Polmyxa betae. Until today, the profitability of the world-wide sugar beet production can only be assured by the use of partially resistant genotypes. However, recent observations from several regions of the world have shown that some isolates are able to overcome the virus resistance in sugar beet, probably due to viral mutations, which are neither caused by the fungal vector nor by any interactions with other pathogens. Additionally, greenhouse trials indicate that temperature has no influence on the performance of BNYVV resistant cultivars. Until now, the responsible resistance mechanism as well as the reasons for resistance breaking and the conditions of selection pressure on the virus population are totally unclear. However, the composition of the BNYVV pathogenicity factor P25 is responsible, among other factors, for the increased aggressiveness of certain isolates. Extensive research efforts are needed to better understand the host-pathogen interaction in order to secure the stability of BNYVV resistance by breeding.