IN AN ELITE CROSS OF MAIZE A MAJOR QUANTITATIVE TRAIT LOCUS CONTROLS 1 4 OF THE GENETIC-VARIATION FOR GRAIN-YIELD/

Quantitative trait loci (QTLs) for grain yield, dry matter content and test weight were identified in an F-2 segregating population derived from a single cross between two elite maize lines (B73 and A7) and tes t-crossed to two genetically divergent inbreds. Most of the QTLs infer red were consistent across locations, indicating that the expression o f the genes influencing the traits under investigation was largely ind ependent of the environment. By using two different tester lines we fo und that QTLs exhibited by one tester may not necessarily be detected with the second one. Only loci with larger effects were consistent acr oss testers, suggesting that interaction with tester alleles may contr ibute to the identification of QTLs in a specific fashion. Analysis ac ross both testers revealed four significant QTLs for grain yield that explained more than 35% of the phenotypic variation and showed an over all phenotypic effect of more than 2 t/ha. The major QTL for grain yie ld, located in the proximity of the Nucleolus Organiser Region, accoun ted for 24.5% of the phenotypic variation for grain yield and showed a n average effect of allele substitution of approximately 1 t/ha. Marke r-assisted introgression of the superior A7 allele at this locus in th e B73 genetic background will not differ from qualitative trait introg ression and will eventually lead to new lines having superior testcros s performance.