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Effect of Root System Genotype and Nitrogen Fertility on Physiological Differences between Burley and Flue-Cured Tobacco. I. Single Leaf Measurements¹

Burley and flue-cured tobacco (Nicotiana tabacum L.) cultivars differ in several phenotypic and chemical characteristics. This study was conducted to characterize differences between representative burley and flue-cured cultivars and to determine the root system influence on shoot physiology. Control and reciprocally grafted plants of burley ‘Ky 14’ and flue-cared ‘Speight G 28’ were grown in the greenhouse at two levels of N fertilization. Leaves were sampled from 10 days before to 30 days after topping (DAT). At both N levels, the genotype of the root system did not influence any of several parameters measured. This result was clearly indicated by total shoot dry weights that, at the final sampling, were higher at both N levels for G 28 shoots regardless of the genotype of the root system. Chlorophyll concentration was consistently higher for G 28 compared to Ky 14 at both N levels. At high N, CO₂ exchange rates were similar and declined over time for both tobacco types. At low N, however, higher CO2 exchange rates were maintained for G 28 compared to Ky 14 until 20 DAT and this result appeared to be due in part to a differential decline in Rnbisco concentration. Leaf expansion and dry weight accumulation were decreased, and specific leaf weight increased by the low-N treatment. For Ky 14, but not G 28, low N resulted in cessation of leaf expansion and dry weight accumulation after 20 DAT. For the high-N treatment, G 28 accumulated leaf dry weight to a greater extent than Ky 14, and at both N levels G 28 had significantly greater specific leaf weight than Ky 14. The results indicated that the burley cultivar was more sensitive to Iow-N fertility than the flue-cured cnltivar, and the root system was not a factor in the expression of physiological differences observed in the shoot.

Key Words: Yb genes • Nitrogen effeciency • Nicotiana tabacum L. • Nitrogen fertilization • Chlorophyll • Carbon dioxide exchange rate • Rubisco

² Plant physiologists, USDA; agronomist, USDA; and professor of Agronomy, Univ. of Kentucky, Lexington, KY 40546.

Received for publication July 9, 1986.