Abstract
AbstractOver the last three decades, the control of Beet necrotic yellow vein virus (BNYVV) in sugar beet has relied on the cultivation of varieties harbouring the Rz1 resistance gene. The strong selection pressure on BNYVV has favoured the development of resistance‐breaking strains that display mutations at amino acid positions 67–70 (tetrad) in the pathogenicity factor P25 and strains possessing an additional RNA component (RNA5). To evaluate the durability of Rz1 resistance, it is essential to monitor the ongoing virulence development in BNYVV populations. Therefore, we characterized BNYVV populations from different fields in Europe suspected to possess resistance‐breaking properties. The ability to overcome Rz1 resistance could be confirmed for several populations in greenhouse bait plant tests using susceptible and resistant genotypes. These populations were able to accumulate similar virus concentrations in both genotypes. Most of the populations harboured multiple P25 tetrad variants, but there was no obvious effect of the sugar beet genotype on their composition. The strong selection pressure on P25 was reflected by the overall high number of P25 haplotypes with several amino acids under positive selection. Two different RNA5 species closely related to either the French or the Asian RNA5 type were additionally identified in some populations. Finally, high‐throughput sequencing revealed the formation of genetic reassortments between different virus types, but the overall sequence diversity within BNYVV populations was relatively low and not affected by the genotype. Our results highlight the ongoing adaption of BNYVV towards Rz1 resistance, stressing the importance of alternative resistance sources.
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