Effects of Host Resistance and Soil Fumigation on Thielaviopsis basicola and Development of Black Root Rot on Burley Tobacco. H. D. Shew, Associate Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695. P. B. Shoemaker, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695. Plant Dis. 77:1035-1039. Accepted for publication 24 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-1035.

Cultivars of burley tobacco (Nicotiana tabacum) with different levels of resistance to Thielaviopsis basicola were planted in fields naturally infested with the pathogen. Severity of black root rot and populations of T. basicola were determined at transplant, midseason, and after final harvest. Cultivars with monogenic resistance to T. basicola derived from Nicotiana debneyi developed little or no root rot in all tests and suppressed pathogen reproduction during the growing season. The severity of root rot and the reproduction of T. basicola were not related to the level of partial resistance. In fact, cultivars with moderate levels of partial resistance frequently had higher root rot severity and similar or greater final populations of T. basicola than did cultivars with low levels of resistance. Moderately resistant cultivars yielded well even with high root rot severity. The effects of soil fumigation on disease and pathogen population dynamics were mixed. In some tests, fumigation significantly increased yield and decreased root rot severity and pathogen population; whereas in other tests, fumigation had little effect on the disease or the pathogen and failed to increase yields. Partial and complete resistance and, in some situations, soil fumigation are effective in the short- and long-term management of black root rot on burley tobacco.