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Evaluation and Induction of Resistance to Blue Mold in Tobacco Genotypes Differing in Contents of Duvatrienediols. M. N. Rao, Department of Plant Pathology, University of Kentucky, Lexington 40546-0091; M. R. Siegel(2), M. T. Nielson(3), M. D. Wiglesworth(4), H. R. Burton(5), and J. Kuc (6). (2)(4)(6)Department of Plant Pathology, University of Kentucky, Lexington 40546-0091; (3)(5)Department of Agronomy, University of Kentucky, Lexington 40546-0091. Phytopathology 79:271-275. Accepted for publication 12 September 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-271.

The a- and -4, 8, 13-duvatriene-1, 3-diols (DVT) are fungitoxic leaf-surface components of tobacco. Tobacco Introductions (TI), double haploid breeding lines, and cultivar Ky 14, with different DVT contents, were evaluated for resistance to blue mold caused by Peronospora tabacina Adam. DVT contents varied significantly in plants grown at different times of the year and increased with age. TI 1068 and the double haploid breeding lines, DH 944-1, DH 909-2, and DH-960, had higher DVT contents than Ky 14 and were more resistant to blue mold than Ky 14. However, although DH 909-2 was the most resistant genotype in greenhouse tests, it did not have the highest DVT contents. TI 1406, with lower contents of DVT than Ky 14, was somewhat more susceptible in greenhouse tests and considerably more susceptible in field tests. TI 1112, however, with little or no DVT, was highly resistant in greenhouse and field tests. In greenhouse tests, systemic resistance was induced in all types of tobacco by stem injection with sporangiospores of P. tabacina, except in TI 1112, which already was highly resistant. DVT contents did not significantly change in stem-injected plants. Removal of DVT by acetone dipping increased susceptibility to blue mold in the early stages of growth, but not in the later stages of field-grown tobacco, which contained DVT. For all genotypes, the oldest plants sampled in the field test (83 days after transplanting) appeared immune. Linear correlations of disease with DVT for individual sampling dates indicated no significant effect of variation in DVT contents among genotypes on disease severity. The disease resistance-DVT relationship is very complex. DVT contents were apparently not responsible for induced resistance or the high resistance of plants sampled late in the season (83 days after transplanting). DVT contents are not the only factors determining resistance to blue mold; however, they may have a contributory role.