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Ending the game of cat-and-mouse between tobamoviruses and their resistance genes

Shinya Tsuda: Central Region Agricultural Research Center, NARO

<div>Resistance genes are powerful tools to control plant viral diseases, against which no agricultural chemicals are available. However, viruses can obtain the abilities to overcome those resistance gene(s) through changes in their genomes, such as recombination or nucleotide substitutions. The genome of tobamoviruses can encode avirulence factors that elicit resistance controlled by a cognate dominant host gene, viral coat protein for four alleles consisting of <em>L<sup>1</sup></em> to <em>L<sup>4</sup></em> in pepper, and viral movement protein for two alleles of <em>Tm-2</em> and <em>Tm-2<sup>2</sup></em> in tomato, for instance. In green pepper cultivation fields in Japan, the <em>L<sup>3</sup></em> resistance gene can successfully prevent tobamoviral diseases in most cases. However, a virulent isolate of tobamoviruses has developed the ability to overcome the <em>L<sup>3</sup></em> resistance gene. Similarly, another variant has been discovered that is able to overcome the <em>L<sup>4</sup></em> resistance gene in the past decade. In tomato cultivation, emergence of several resistance-breaking tobamovirus variants has sometimes been found in Japan, which are capable of infecting tomato cultivars carrying resistant genes; <em>Tm-2</em> and/or <em>Tm-2<sup>2</sup></em>. Experts should make effort to achieve successful management of these resistance genes for sustainable crop production, which must be supported by integrated pest management strategies and scientifically sound evidences, although technological strategies applicable to control viral diseases in field are currently limited.</div>

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