Fusarium wilt of watermelon, caused by Fusarium oxysporum f. niveum, can be a limiting factor in California watermelon production. Warm weather, which favors watermelon production, also favor the disease. The fungus lives in t he soil for many years, and therefore rotation, although helpful, is not the answer to the problem. Studies were initiated in 1971 to test various watermelon cultivers for resistance to the Fusarium wilt fungus.