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The Secreted in Xylem Gene Profile of the Spinach Fusarium Wilt Pathogen

Alex Batson: Washington State University

<div>The maritime Pacific Northwest (PNW) is the only region of the United States suitable for production of spinach seed, which requires a long day length and cool, dry summers to yield high quality seed. The greatest limitation to spinach seed production in the PNW is Fusarium wilt caused by <em>Fusarium oxysporum </em>f. sp. <em>spinaciae </em>(<em>Fos</em>). There are no known races of <em>Fos</em> and resistance to this pathogen appears quantitative. Unique combinations of 14 effector genes called <em>Secreted in Xylem </em>(<em>SIX</em>) genes, originally identified in <em>F. oxysporum </em>f. sp. <em>lycopersici</em>, have been detected in other formae speciales (ff. spp.). PCR assays were used to target all 14 <em>SIX </em>genes of >40 <em>F. oxysporum </em>isolates representing ff. spp. <em>cepae</em>, <em>ciceris</em>, <em>lycopersici</em>, <em>pisi</em>, and <em>spinaciae</em>. Out of 19 <em>Fos </em>isolates tested, 10 had <em>SIX8</em> and 17 had <em>SIX14</em>. The other ff. spp. had various combinations of 14 <em>SIX </em>genes that have been reported previously. Two and four isolates that were not pathogenic to spinach but were obtained from spinach plants or from soil in which spinach was grown, also tested positive for<em> SIX8 </em>and <em>SIX14</em>, respectively<em>.</em> Phylogenetic analyses of <em>SIX8 </em>and <em>SIX14</em> DNA sequences indicated that the <em>Fos </em>isolates are divergent from those of other ff. spp. tested. Characterizing the <em>SIX</em> effector profile of <em>Fos </em>will assist with developing molecular diagnostic tools for the pathogen and breeding cultivars with improved resistance to Fusarium wilt.</div>