Direct mapping of density response in a population of B73 x Mo17 recombinant inbred lines of maize (Zea Mays L.).

Maize yield per unit area has dramatically increased over time as have plant population densities, but the genetic basis for plant response to density is unknown as is its stability over environments. To elucidate the genetic basis of plant response to density in maize, we mapped QTL for plant density-related traits in a population of 186 recombinant inbred lines (RILs) derived from the cross of inbred lines B73 and Mo17. All RILs were evaluated for growth, development, and yield traits at moderate (50 000 plants per hectare) and high (100 000 plants per hectare) plant densities. The results show that genetic control of the traits evaluated is multigenic in their response to density. Five of the seven loci significant for final height showed statistical evidence for epistatic interactions. Other traits such as days to anthesis, anthesis-to-silking interval, barrenness, ears per plant, and yield per plant all showed statistical evidence for an epistatic interaction. Locus by density interactions are of critical importance for anthesis-to-silking interval, barrenness, and ears per plant. A second independent experiment to examine the stability of QTL for barrenness in a new environment clearly showed that the multilocus QTL were stable across environments in their differential response to density. In this verification experiment, the four-locus QTL was used to choose lines with the four unfavorable alleles and compare them with the lines with four favorable alleles and the effect was confirmed.