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Effects of Nicotiana longiflora Cav. Resistance to Race 0 Phytophthora parasitica var. nicotianae on Agronomic and Chemical Traits in Burley Tobacco¹

Interspecific transfers of genes for disease resistance have been used extensively in breeding tobacco (Nicotiana tabacum L.), but some transferred segments have changed agronomic and chemical traits. Experiments were conducted with isogenic or near-isogenic lines to assess the effects of the N. longiflora Cav. resistance to race 0 of Phytophthora parasitica var. nicotianae (Breda de Haan) Tucker on several characteristics of burley tobacco. Seven generations of backcrossing were used to develop a susceptible and a resistant selection in each of eight cultivar backgrounds. When compared with the susceptible cultivars and susceptible selections, the resistant selections were consistently lower in number of leaves and total alkaloid content. For days to flower, plant height, leaf width, and yield, significant family x selection interactions indicate that effects of resistance varied in different genetic backgrounds. In all statistically significant comparisons, the resistant selection was earlier flowering, was shorter, had narrower leaves, or was lower yielding than the susceptible cultivar.

The observed effects of race 0 resistance on agronomic and chemical traits should not prevent the development of acceptable cultivars with the resistant allele if germplasm sources and selection procedures are carefully chosen. Available information indicates that several monogenic disease resistance genes can be incorporated into burley cultivars with minimal changes in quantitatively inherited traits.

Key Words: Nicotiana tabacum L. • Isogenic lines • Disease resistance • Fungal disease • Black shank disease

² Research geneticist, USDA-SEA-AR, P.O. Box 867, Beckley, WV 25801; research agronomist, USDA-SEA-AR, Dep. of Plant Pathology, Univ. of Kentucky, Lexington, KY 40546; and professor, Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546.

Received for publication May 18, 1981.