Soil-borne populations of Fusarium oxysporum f. sp vasinfectum, a cotton wilt fungus in California fields

High populations of Fusarium oxysporum f. sp. vasinfectum, mostly between 100 and 1000 propagules/gram of soil, were found in 10 field soils assayed eight times during 10 yr after susceptible and infected cotton crops had been grown. During some of the years following the cotton crops, cotton and perennial crops such as grapevines and almond trees were grown. Among the isolates of F. oxysporum sp. vasinfectum two culture types were found: low sporing and high sporing types. The high sporing type was more frequently isolated from soil. The two types were further characterized by RAPD analysis and pathogenicity tests.