Measuring the Potential Contribution of Plant Breeding to Crop Yields: Flue‐Cured Tobacco, 1954–87

Measurements are made of plant breeders' success in increasing potential flue‐cured tobacco yields from 1954 to 1987 in North Carolina. Nongenetic sources of yield increases are measured by the yield levels of a standard variety. New genetic material accounted for between 20% and 35% of yield increases on research station plots in the three tobacco‐growing regions. Recent genetic contributions have been small. The slowdown is not attributable to a federal tobacco policy shift in 1965 that slowed the growth in grower yields. There is also no evidence that tobacco breeders increased their output in response to the Plant Variety Protection Act of 1970.