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The Evolutionary History of Beet necrotic yellow vein virus Deduced from Genetic Variation, Geographical Origin and Spread, and the Breaking of Host Resistance

February 2011 , Volume 24 , Number  2
Pages  207 - 218

Soutaro Chiba,1 Hideki Kondo,1 Masaki Miyanishi,1 Ida Bagus Andika,1 Chenggui Han,2 and Tetsuo Tamada1

1Institute of Plant Science and Bioresources, Okayama University, Kurashiki, Okayama, 710-0046, Japan; 2State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, China

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Accepted 20 October 2010.

Beet necrotic yellow vein virus (BNYVV) is an economically important pathogen of sugar beet and has been found worldwide, probably as the result of recent worldwide spread. The BNYVV genome consists of four or five RNA components. Here, we report analysis of sequence variation in the RNA3-p25, RNA4-p31, RNA2-CP, and RNA5-p26 genes of 73 worldwide isolates. The RNA3-p25 gene encodes virulence and avirulence factors. These four sets of gene sequences each fell into two to four groups, of which the three groups of p25 formed eight subgroups with different geographical distributions. Each of these subgroup isolates (strains) could have arisen from four original BNYVV population and their mixed infections. The genetic diversity for BNYVV was relatively small. Selection pressure varied greatly depending on the BNYVV gene and geographical location. Isolates of the Italy strain, in which p25 was subject to the strongest positive selection, were able to overcome the Rz1-host resistance gene to differing degrees, whereas other geographically limited strains could not. Resistance-breaking variants were generated by p25 amino acid changes at positions 67 and 68. Our studies suggest that BNYVV originally evolved in East Asia and has recently become a pathogen of cultivated sugar beet followed by the emergence of new resistance-breaking variants.

© 2011 The American Phytopathological Society