Efficiency of Rz1-based rhizomania resistance and molecular studies on BNYVV isolates from sugar beet cultivation in Greece Ourania Pavli & Marcel Prins & Rob Goldbach & George N. Skaracis Accepted: 26 May 2010 /Published online: 9 April 2011 # KNPV 2011 Abstract A survey was carried out to investigate the current situation concerning rhizomania disease inci- dence in sugar beet cultivation of Greece. A system- atic field evaluation over locations and years revealed a consistent disease severity pattern according to favourable agroclimatic conditions and pointed to the so far effectiveness of the Rz1 gene-based resistance, as no major disease outbreaks were observed. Molecular analyses aiming at the character- ization of the type and genetic diversity of the virus further confirmed the widespread occurrence of BNYVV in the country, as evidenced by RT-PCR amplification of all five known genomic molecules and nested-PCR assays. None of the isolates con- tained an RNA 5, typically found in pathotype P. On the basis of RFLP patterns, all BNYVV isolates analysed were classified as pathotype A. Sequence determination of the full-length RNA 3-encoded p25 protein, responsible for symptom development, revealed amino acid motifs ACHG/VCHG in the hypervariable region aa 67–70 . The presence of valine in position 67 did not appear associated with increased pathogenicity and resistance breaking prop- erties, as earlier reported. Keywords Beet necrotic yellow vein virus . Rz1-based resistance . RNA 3-encoded p25 protein . Rhizomania . Sugar beet Introduction Rhizomania disease of sugar beet (Beta vulgaris subsp. vulgaris) was initially described by Canova in Italy in the mid 50’ s and has since been reported in most crop producing countries worldwide (Tamada 1999). The disease causes severe economic losses as a consequence of a dramatic reduction in root yield and sugar content. Rhizomania disease symptoms include massive lateral root proliferation resulting in a beard-like appearance, constriction of the main taproot and stunting of the infected plant (Tamada 1999). The disease is caused by Beet necrotic yellow vein virus (BNYVV) (Tamada and Baba 1973) which Eur J Plant Pathol (2011) 130:133–142 DOI 10.1007/s10658-010-9639-4 O. Pavli : R. Goldbach Department of Plant Sciences, Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands O. Pavli (*) : G. N. Skaracis Department of Crop Sciences, Laboratory of Plant Breeding and Biometry, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece e-mail: ourania.pavli@wur.nl M. Prins Keygene N.V., Agro Business Park 90, 6708 PW Wageningen, The Netherlands