Genetic Improvement Estimates, from Cultivar × Crop Management Trials, Are Larger in High-Yield Cropping Environments.

Soybean [Glycine max (L.) Merr.] genetic improvement studies conducted under different stresses have provided conflicting results while maize (Zea mays L.) studies have shown that new cultivars were tolerant to a wide range of stresses. Using 25 genetic improvement studies from the literature, the objectives of this study were to compare estimates of genetic improvement under a range of yield capacities and also to determine the Finlay-Wilkinson adaptability of old to newer cultivars. The 25 genetic improvement studies were performed under a range of yield capacities due to varying density, fertility, irrigation, fungicide treatments, or year-to-year variation. Genetic improvement rates for each experiment were estimated from linear regression of cultivar yield on year of release. A cultivar's adaptability was estimated from regression of cultivar yield on site yield. In general, higher estimates of genetic gain were found in highyielding environments regardless of whether the higher yields were provided by reducing stress (controlling weeds or diseases, increasing nitrogen or water) or increasing stress using higher plant densities. Newer cultivars had higher adaptability values, indicating they are better adapted to high-yield environments. Older cultivars appear to have little utility for current use in any of the cropping systems in these studies. Plant breeders need to consider the possibility of lower genetic progress if using lower-yieldpotential testing environments such as reduced fertility or weed control. The use of high-yield sites may maximize genetic progress even if it does not reflect current producer environments. [ABSTRACT FROM AUTHOR]