Distribution of resistance-breaking isolates of beet necrotic yellow vein virus differing in virulence in sugar beet fields in Turkey

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV), is one of the most devastating diseases on sugar beet throughout the world. A total of 235 BNYVV-infested soil samples taken from 29 provinces during the growing seasons of 2004-2005 and 2010-2011 were investigated for resistance-breaking properties of BNYVV isolates. BNYVV resistant (Rz1, Rz1 + R2, Rz1 + C48 + minor genes) and susceptible (rz1) sugar beet cultivars were grown in the BNYVV-infested soils by the bait plant technique, and virus infection was evaluated based on disease symptom and DAS-ELISA. Of the soil samples tested, 57.4% produced infection in the roots of sugar beet cultivar (cv.) containing the Rz1 gene, 51.9% in cv. carrying the Rz1 + Rz2 and 18.9% in cv. carrying the Rz1 + C48 + minor genes. Also, the presence of Beet soil-borne virus (BSBV) was evaluated by TAS-ELISA. Additionally, the presence of BNYVV RNA-5 component was investigated by RT-PCR using the primers specific for p26 coding region. Our results revealed that BNYVV isolates compromising resistance genes are highly common and widespread in sugar beet production areas in Turkey, and it seems unlikely that BSBV and/or RNA-5 were directly involved in RB-event.