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Survival of Pseudomonas solanacearum in Selected North Carolina Soils. W. C. Nesmith, Department of Plant Pathology, University of Kentucky, Lexington 40546; S. F. Jenkins, Jr., Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 73:1300-1304. Accepted for publication 25 April 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1300.

Survival of Pseudomonas solanacearum was monitored from one growing season to the next in microplots containing soils from four North Carolina sites that varied greatly in the occurrence of bacterial wilt of tomato from year to year. The microplots were infested with 2.5 x 109 colony-forming units of P. solanacearum (race 1, biotype I) per gram of soil in September after soil in one-half of the plots was fumigated with methyl bromide. Survival was monitored by using a selective medium and susceptible tomato plants. The bacterial population declined more rapidly in the soils collected from nonpersistent sites than in soils from persistent sites. Fumigation of soils from nonpersistent sites was only partially effective in improving persistence and slowing the rate of decline of P. solanacearum. Populations of P. solanacearum declined rapidly upon addition to soil. Six months after infestation, tomato seedlings were planted directly into the microplots, because the bacterium was no longer detectable by testing it with the selective medium. Bacterial wilt on tomatoes did not develop in the nonfumigated soils collected from nonpersistent sites, but was common within 30 days after transplanting in fumigated soils and in both fumigated and nonfumigated soils collected from persistent sites. In greenhouse experiments, disease development was similar in steamed and nonsteamed soils regardless of the collection site, if tomato plants and inoculum of P. solanacearum were added simultaneously. However, when soils were infested with the bacteria and held for 60 days before the tomato seedlings were transplanted, significantly less disease developed in nonsteamed soils collected from nonpersistent sites, compared to steamed soils from the same site or steamed and nonsteamed soils from the persistent site. This indicates that suppressive soil factors (possibly of biological origin) exist at sites where P. solanacearum does not persist from season to season.

Additional keywords: Lycopersicum esculentum.