Allelic Eff ect Variation at Key Photoperiod Response Quantitative Trait Loci in Maize

The genetic diversity of elite temperate maize (Zea mays L.) germplasm is reduced relative to global intraspecifi c variation, resulting from intense phenotypic selection for increased yield and crop uniformity over the past century (Goodman, 2004; Tenail-lon et al., 2001). The relatively narrow genetic base of temperate maize renders it more vulnerable to evolving pathogen biotypes and may limit future gains in productivity (Smith, 2007). Geneti-cally more diverse tropical maize represents a valuable genetic resource that could be used to enhance the diversity and pro-ductivity of temperate maize (Goodman, 2004; Gouesnard et al., 1996). Unfortunately, most tropical germplasm is poorly adapted to temperate growing environments. A major component of the poor adaptation of tropical maize to temperate environments is the response of tropical germplasm to long-day photoperiods. At daylengths greater than 13 h, photoperiod-sensitive maize exhib-its delayed fl owering, increased plant height (PH), and a greate