Effects of two-year crop rotations and cultivar resistance on bacterial wilt in flue-cured tobacco.
The incidence of bacterial wilt, caused by Pseudomonas solanacearum, was reduced and the yield of flue-cured tobacco was increased by cultivar resistance and by 1-yr rotation with maize, fescue (Festuca sp.) or soyabeans as compared with continuous tobacco. In general, crop value and yield were higher and disease index lower when tobacco was grown after soyabeans than after fescue, maize or tobacco. The value, yield and disease index for tobacco grown after maize and after fescue did not differ. In contrast, value and yield were lowest and disease index was highest for continuous tobacco. The rotation used had a greater effect on the disease index in the more susceptible of the 3 tobacco cultivars planted. The disease index was 2.7-4.8 times higher in the more susceptible cultivar, whereas yields were 1.1-2.3 times higher in 2 of the 3 yr for the more resistant cultivar. When plots were fumigated with 1,3-dichloropropene + chloropicrin, yield was 8.4% higher but the disease index was not affected.