Allelic Effect Variation at Key Photoperiod Response Quantitative Trait Loci in Maize

Tropical maize (Zea mays L.) represents a valu- able genetic resource containing unique alleles not present in elite temperate maize. The strong delay in fl owering in response to long daylength photoperiods exhibited by most tropical maize hinders its incorporation into temperate maize breeding programs. We tested the hypothesis that diverse tropical inbreds carry alleles with similar effects at four key photoperiod response quantitative trait loci (QTL) previously identifi ed in maize. Four tropical maize inbreds were each crossed and backcrossed twice to the temper- ate recurrent parent B73 to establish four sets of introgression lines. Evaluation of these lines under long daylengths demonstrated that all four QTL have signifi cant effects on fl owering time or height in these lines, but the functional allelic effects varied substantially across the tropical donor lines. At the most important pho- toperiod response QTL on chromosome 10, one tropical line allele even promoted earlier fl ower- ing relative to the B73 allele. Signifi cant allelic effect differences among tropical founders were also demonstrated directly in an F 2 population derived from the cross of Ki14 and CML254. The chromosome 10 photoperiod response QTL position was validated in a set of heterogeneous inbred families evaluated in fi eld tests and in controlled environments.