Genetic variation in Verticillium dahliae populations in southwestern Ontario processing tomato fields

摘要

Tomato is an economically important crop in Kent and Essex Counties of southwestern Ontario. Verticillium wilt of tomato has been controlled in this region for several decades, through the widespread cultivation of Verticillium-resistant (Ve) varieties. Race 2 of V. dahliae, which can infect these cultivars, was first reported in Ontario in 1989 (1), and a 1993-1994 survey of Essex Co. processing tomato fields showed that race 2 is now prevalent in this region (4). In Essex Co., tomato is cultivated intensively, and corn is typically used as a rotation crop. Rotations tend to be short (2 to 3 yr), and may even include potato. The tomato fields are also frequently in close proximity to potato fields, in contrast, in adjacent Kent Co. commercial growers preferentially select fields in which tomato has either never been grown, or has not been grown for many years. Potatoes are also not widely grown commercially in this region, and verticillium wilt is currently not considered a disease problem. To determine if the Verticillium dahliae populations differed in the processing tomato fields in these two counties, we assayed V. dahliae levels in soil and plant samples collected from Kent Co. fields, and characterized Essex Co. race 2 V. dahliae isolatesand Kent Co. isolates by DNA fingerprinting methods.