Dwarf8 polymorphisms associate with variation in flowering time

Historically, association tests have been used extensively in medical genet ics(1-2), but have had virtually no application in plant genetics. One obst acle to their application is the structured populations often found in crop plants(3), which may lead to nonfunctional. spurious associations(4). In t his study. statistical methods to account for population structure(5) were extended for use with quantitative variation and applied to our evaluation of maize flowering time. Mutagenesis and quantitative trait locus (QTL) stu dies suggested that the maize gene Dwarf8 might affect the quantitative var iation of maize flowering time and plant height(6-8). The wheat orthologs o f this gene contributed to the increased yields seen in the 'Green Revoluti on' varieties(6). We used association approaches to evaluate Dwarf8 sequenc e polymorphisms from 92 maize inbred lines. Population structure was estima ted using a Bayesian analysis(4) of 141 simple sequence repeat (SSR) loci. Our results indicate that a suite of polymorphisms associate with differenc es in flowering time, which include a deletion that may alter a key domain in the coding region. The distribution of nonsynonymous polymorphisms sugge sts that Dwarf8 has been a target of selection.