Trends in genetic variance components during 30 years of hybrid maize breeding at the University of Hohenheim

The ratio of variance due to specific vs. general combining ability (GCA) (sigma(2)(SCA):sigma(2)(GCA)) is of central importance for predicting hybrid performance from GCA effects. The objectives of our study were to (1) analyse the changes in estimates of sigma(2)(GCA), sigma(2)(SCA) and their ratio during 30 years of hybrid maize breeding and (2) compare the observed trends in genetic variances with those expected under a simple genetic model. We analysed multilocation yield trials based on the North Carolina Design II conducted in the maize breeding programme of the University of Hohenheim from 1975 to 2004 for grain yield (GY) and dry matter content (DMC). GY showed a significant (P < 0.05) annual increase of 0.17 Mg/ha, but no linear trend was found for DMC. Since the beginning of hybrid breeding at the University of Hohenheim, the sum of estimates of sigma(2)(GCA) of the flint and dent heterotic groups were higher than the estimates of their sigma(2)(SCA). This predominance did not change with ongoing inter-population improvement. Consequently, superior hybrids can be identified and selected mainly based on their prediction from GCA effects.