Many crosses made by midwestern U.S. soybean breeders are made between adapted genotypes and genotypes of later maturity. Due to a short growing season, soybean breeders in the northern U. S. are often unable to sufficiently delay planting of adapted genotypes to synchronize flowering with genotypes of later maturity. Photoperiod chambers are expensive and covering plants is time consuming and often produces cleistogamous flowers.
Beaver, J. S. and Nelson, R. L.
"Research Notes: Effect of grafting date and maturity of the stock on the flowering behavior of soybean scions,"
Soybean Genetics Newsletter: Vol. 8
, Article 13.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol8/iss1/13