Wednesday, November 7, 2007 - 10:00 AM
255-3
Three Cycles of Recurrent Selection for Increased or Decreased Recombination Frequency in Zea mays.
Dandan Li and Todd Pfeiffer. University of Kentucky, University of Kentucky, 310 Plant Science Building 0312, Lexington, KY 40546
The variability among progeny in a plant breeding population depends on the amount of recombination that occurs in meiosis preceding selection. The recombination is either interchromosomal recombination arising from the independent assortment of chromosomes or intrachromosomal recombination resulting from crossing over during pairing of homologous chromosomes. Crossing over is not a constant value; it differs based on background genotype. The objective of the present research was to determine if selection for high and low recombination frequency (RF) is effective. Three cycles of recurrent selection for increased or decreased crossing over were completed in the Iowa Stiff Stalk Synthetic maize population. Testcrosses measured male recombination frequency on three chromosomes: 4, su1-c2; 5, a2-bt1-pr1; and 9, sh1-bz1-wx1. Sixty plants from each of three populations (cycle 0 [C0], cycle 3 high recombination [C3HR], and cycle 3 low recombination [C3LR]) were evaluated along with the parental lines for each cycle of selection. Analyses of variance were conducted for RF at chromosome regions a2-bt1, bt1-pr1, a2-pr1 and su1-c2. Population effect was highly significant for all four chromosome regions with populations derived following selection for high or low RF on these chromosomes producing individuals exhibiting high or low RF, respectively. At the a2-bt1 region the mean RF of the C0 population was 0.046, of C3HR was 0.062, and of C3LR was 0.029. At chromosome region bt1-pr1 the mean RF of the C0 population was 0.13, of C3HR was 0.16, and of C3LR was 0.10. When these RF are added together, the mean RF difference between each population for the entire region a2-pr1 is also highly significant. At the su1-c2 region the mean RF of the C0 population was 0.37, of C3HR was 0.38, and of C3LR was 0.32. The mean RF difference between C0 and C3HR is significant at P<0.05, and the mean RF difference between C0 and C3LR is highly significant. From the above results we conclude that modification by selection for high or low RF has been successful. Population changes for chromosome 9 will be reported at the conference.