A spontaneous non-pathogenic variant (Cong:1-2) derived from Fusarium oxysporum f. sp. conglutinans (Cong: 1-1), a causal agent of cabbage yellows, carries biocontrol activity for cabbage yellows. We found a GMC oxidoreductase (ODX1) among the proteins expressed much more in Cong:1-2 than Cong:1-1 by 2D-DIGE comparison. GMC oxidoreductases have been reported to be involved in biocontrol activity of several plant pathogenic fungi. The gene encoding ODX1 in Cong:1-2 was cloned, and targeted disruption of the gene in Cong:1-2 did not affect its biocontrol activity, suggesting that GMC oxidoreductase is dispensable for biocontrol activity in the fungal biocontrol agent.