Variation of mutations in AVR genes in the field isolates of the tomato wilt fungus, Fusarium oxysporum f. sp. lycopersici
Tsutomu Arie: Tokyo Univ of Agric & Tech (TUAT)
<div>Race-cultivar interactions between the tomato wilt fungus, <em>Fusarium oxysporum</em> f. sp. <em>lycopersici</em> (<em>Fol</em>) and tomato (<em>Solanum lycopersicum</em>) are determined by the interactions between the avirulence genes (<em>AVR1</em>, <em>AVR2</em> and <em>AVR3</em>) carried by <em>Fol</em> and the corresponding resistance genes (<em>I</em>, <em>I2</em> and <em>I3</em>) carried by tomato. The avirulence genes often exist on small conditionally dispensable (CD) chromosomes, which are not necessary for growth but are responsible for pathogenicity. Three races have been reported in <em>Fol</em> and these races can be determined by the combination of carrying avirulence genes; race 1 (<em>AVR1 AVR2 AVR3</em>), race 2 (<em>avr1</em> <em>AVR2 AVR3</em>) and race 3 (<em>avr1</em> <em>avr2 AVR3</em>). A collection of isolates of races 2 and 3 of <em>Fol</em> was made from the fields in Japan from 2000 to 2017. In the nine isolates analyzed, we found 5 kinds of mutations (<em>avr1</em><sup>null</sup>, <em>avr1</em><sup>th380</sup>, <em>avr1</em><sup>th685</sup>, <em>avr1</em><sup>tf-380</sup>, and <em>avr1</em><sup>5’-ND</sup>) in <em>AVR1</em>, and 4 kinds (<em>avr2</em><sup>null</sup>, <em>avr2</em><sup>G121A</sup>, <em>avr2</em><sup>T122A</sup>, and <em>avr2</em><sup>C146T</sup>) in <em>AVR2</em>. None of the nine isolates had the identical combination of mutations in <em>AVR1</em> and <em>AVR2</em>, even though some of the isolates are phylogenetically very close. These suggest that race differentiation of <em>Fol</em> in the field is more diversified than expected. Because this observation possibly relates to the fact that the avirulence genes exist on CD chromosomes, we will discuss the karyotypes of the field isolates, too.</div>
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