Evaluation of Host Resistance and Soil Fumigation for the Management of Black Root Rot of Tobacco in Ontario.

Black root rot of tobacco, caused by the soilborne fungus Thielaviopsis basicola, is a serious problem in many tobacco (Nicotiana tabacum L.)-growing regions of the world. In Ontario, the disease is favored by cool, wet soil conditions and heavy textured or poorly drained soils. Yield loss can be severe under these conditions and fumigants containing chloropicrin are used extensively for controlling the disease. Usually, fumigants control the disease reasonably well, but they are costly and could cause a negative environmental impact. A 2-year study was conducted to evaluate the performance of resistant (AC Gayed) and moderately susceptible (Delgold) tobacco cultivars and soil fumigation to black root rot. T. basicola reduced yield of the susceptible Delgold cultivar. The interaction between genotype and fumigation was significant for most traits examined, indicating that the two genotypes responded differently. Orthogonal comparisons indicate that yield from nonfumigated AC Gayed was higher than that of nonfumigated Delgold. Yield of nonfumigated AC Gayed was also not significantly different from the yield of AC Gayed treated either with Vorlex Plus (1,3-dichloropropene+methyl isothiocyanate) or with Vorlex Plus CP (1,3-dichloropropene+methyl isothiocyanate+chloropicrin). In contrast, the yield of nonfumigated Delgold was lower than Delgold treated with Vorlex Plus CP.