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Virulence of Fusarium oxysporum f. sp. cucumerinum is affected by its successive generations on resistant and susceptible cucumber cultivars

Shidong Li: Institute of Plant Protection, Chinese Academy of Agricultural Sciences

<div><em>Fusarium oxysporum</em> f. sp. <em>cucumerinum</em> (<em>Foc</em>) is the causal pathogen of cucumber Fusarium wilt resulting in losses to cucumber production. To investigate the effects of the selective pressures of host plants on the virulence of <em>Foc</em>, we successively inoculated foc-3b, a low virulence isolate, on resistant and susceptible cucumber cultivars for five generations. Pathogenecity tests showed that virulence of the original isolate diverged after serial passage. The virulence was significantly strengthened on the resistant cultivar and weakened on the susceptible plants (<em>P </em>˂ 0.05). The expression of four virulence-related genes of <em>F. oxysporum</em>, G-protein a subunit gene <em>fga1</em>, sucrose non-fermenting 1 gene <em>snf1</em>, F-box protein gene <em>frp1</em>, and Class V chitin synthase gene <em>chsV</em>, was detected using real-time PCR. All 4 genes were significantly up-regulated after serial passage on the resistant cultivar, compared to the original strain, and the expression of <em>snf1</em> was down-regulated in strains re-isolated from the susceptible plants (<em>P </em>˂ 0.05). A significant positive correlation was found between the expression levels of gene <em>snf1</em>, <em>frp1</em> and <em>chsV </em>and disease severity of cucumber Fusarium wilt, suggesting these genes may impact virulence differentiation. This study will improve the management of cucumber Fusarium wilt and provide insight into the mechanisms underlying virulence of <em>F. oxysporum</em>.</div>