|Holland, Jim - Jim|
Submitted to: Genes, Genomes, and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2011
Publication Date: 10/5/2011
Citation: Holland, J.B., Coles, N.D. 2011. QTL controlling masculinization of ear tips in a maize (Zea mays L.) intraspecific cross. Genes, Genomes, and Genomics. 1:337-341. Interpretive Summary: Maize (corn) has distinct male and female flowers. Male flowers appear as tassels at the top of the plant. Female flowers which produce seed appear as ears at the side of the plant. We observed a tropical maize line that produced tassel-like male flower tips at the end of its ears. To discover the genetic control of this trait, we evaluated more than 200 lines derived from the cross of this line to a standard Corn Belt line that produces only normal completely female ears. We found three chromosomal regions that control the variation for this trait. One of these regions is near a previously described region that has a similar effect in the wild relative of maize, teosinte. The other two regions carry genes that make plants sensitive to long daylengths, under which the masculinization occurs. Knowing these genetic regions will help breeders eliminate this unfavorable trait from breeding populations.
Technical Abstract: Maize is unique among cereal grasses because of its monoecious flowering habit. Male flowers are normally restricted to the tassel that terminates the primary shoot, whereas female flowers occur as ears at the terminal nodes of lateral branches. We observed a tropical maize inbred, Ki14, that produces an ear tipped by a staminate (male) spike under certain environmental conditions, such as long daylengths. Recombinant inbred lines derived from the cross between temperate line B97, which was never observed to produce a staminate ear tip, and Ki14 segregated for the trait under long daylengths. Some progeny lines had even longer staminate tips than Ki14 that were male fertile. We mapped three QTL controlling staminate ear tip using a two-part (binomial plus normal) model. A major QTL on chromosome 3 had a large effect on penetrance of the trait (whether a line would produce staminate ear tips or not) as well as its severity (the length of the staminate tip). This QTL appears to be linked to, but at a distinct position from, a previously mapped QTL controlling the proportion of staminate florets in ears in progeny from crosses between maize and teosinte. Two additional QTL affecting staminate ear tip severity overlapped with QTL controlling photoperiod response previously mapped in this population. Alleles conferring photoperiod-sensitivity for delayed flowering at these QTL appear to enhance the production of staminate ear tips under long daylengths.