Evidence for Beet Necrotic Yellow Vein Virus (BNYVV) reassortment and diversity of the P25 avirulence gene in France

Galein, Yann [UCL] Champeil, Agnès [Institut Technique de Recherche sur la Betterave, Paris, France] Escriou, Hervé [Institut Technique de Recherche sur la Betterave, Paris, France] Richard-Molard, Marc [Institut Technique de Recherche sur la Betterave, Paris, France] Legrève, Anne [UCL] Bragard, Claude [UCL]

Since the beginning of 1990, in the region of Pithiviers, the sugar beet crop is under a strong pressure of rhizomania disease. The causal agent,Beet necrotic yellow vein virus (BNYVV) has evolved through the selection pressure linked with the progressive introduction of Rz1 tolerant sugar beets. Field-based research was carried out to analyze both the virus and the vector (Polymyxa betae). A very high diversity of the BNYVV RNA-3 tetrad, indicative of resistance-breaking was evidenced in the Pithiviers region. BNYVV was detected in 835 of the 1058 samples collected between 2008 and 2012. Twenty-one different variants of the highly variable amino acid tetrad at positions 67–70 of p25 were identified, i.e. AYHR, TYHR, SYHG, SYHR, SYHN, SFHG, SCHG, AYPR, AYHG, AFHG, AFHR, AFLG, AFPR, VCHG, VYHG, VYHR, TFPR, AYHT, AYHS and ASHR. The first variant, AYHR, was found most commonly followed by SYHG. In a single sugar beet root, presumptive indications of BNYVV reassortment were found in ca 20 % of the samples. Several different tetrads associated with the A- or B-type were found with the fifth RNA. Moreover, one of the variety Rz1rz1Rz2rz2 showed lower titer with Beet soil-borne virus (BSBV), a Pomovirus associated with rhizomania. This variety showed also lower root symptom and lower virus inoculum potential at the end of the beet season compared to the others. Results will be discussed in comparison with those provided by Schirmer et al . (2005) from the same area