Sugar beet is a major crop in Iran with now nearly 160,000 ha under cultivation. The rhizomania disease of sugar beet is now present in almost all of major sugar beet growing areas within the country. In order to have a clear view over rhizomania situation in Iran, a comprehensive study was conducted. Up to 300 soils and sugar beet samples were collected throughout the country in 2006, using a smart sampling procedure. Out of these 300 samples, 203 proved to be infected by the Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, representing thus 66% of the sugar beet fields sampled. Two different virus types were found by targeted sequence analysis. The RNA-3 p25 gene, involved in the virulence of BNYVV, was then systematically sequenced, with the view of characterizing the virus diversity throughout the country. Seven different variants of the p25 were found in Iran. Most of the Iranian infected samples were related to BNYVV type A, with six different aa tetrads AHHG, ACHG, AYHG, ALHG, AFHR, AFHG and just one in BNYVV type P with a SYHG tetrad. Only 18 mutations at nucleotide level were recorded for the RNA-3 p25 660 nucleotide fragment, resulting in 15 amino acid changes. Such a high ratio of aa changes indicates a strong pressure on the virus, may be due to the recent introduction of tolerant sugar beet cultivars combined to high inoculum potential in Iranian Polymyxa betae-infested soils. Concurrently, soils were also checked for the presence of BSBV and BVQ, two soil-borne pomoviruses often associated with BNYVV. In total, 96 samples out of the 203 BNYVV positive isolates (47,3%) were found positive for the presence of BSBV and 30 (14,7%) for BVQ. Strategies for the management of the viral disease in Iran will be discussed.

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