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Use of Progenitor Species Germplasm for the Improvement of a Cultivated Allotetraploid

The suitability of progenitor species germplasm as a source of genetic variation for the improvement of quantitatively inherited genetic traits in a cultivated allotetraploid species was investigated. Tobacco, Nicotiana tabacum L. cv. SC 58 was doubled with colchicine to the octoploid state and crossed with the diploid progenitor species N. sylvestris Speg. and Comes. The partially fertile pentaploid hybrid was selfed, or backcrossed one generation to SC 58, to increase fertility. Two cycles of a recurrent selection scheme using SC 58 as a tester parent were then followed to concentrate desirable germplasm from N. sylvestris in the species-derived synthetic populations.

The two synthetic populations (Syn I and Syn II), 58, S₁ families, and testcrosses to SC 58 of plants in Syn I which were used to produce Syn II were evaluated in three environments for 11 agronomic and chemical constituents. Significant differences were detected among genetic entries for all characters measured except percent nornicotine in cured leaf, indicating that germplasm from the diploid species, N. sylvestris, had been introgressed into the N. sylvestris genome of tobacco. The potential value of this genetic variation is demonstrated by the fact that Syn I and Syn II yielded 7.7 and 12.9%, respectively, more cured leaf than SC 58. Thus, the breeding technique may be useful in broadening the genetic base for the improve. merit of quantitatively inherited characters in this cultivated species.

Key Words: Genetic vulnerability • Germplasm base • Tobacco • Interspecific hybridization • Recurrent selection • Nicotiana tabacum L. • N. sylvestris Speg. and Comes

² ~Professor of crop science and professors of genetics, respectively, North Carolina State Univ., Raleigh, NC 27607.

Received for publication February 9, 1976.