Three cycles of recurrent selection for altered recombination frequency in maize

The variability among progeny in a plant breeding population depends on the amount of recombination that occurs in meiosis preceding selection. The recombination arises either from the independent assortment of chromosomes or from crossing over during chromosome synapsis. Crossing over is not a constant value; it differs based on background genotype. This research determined the effectiveness of three cycles of recurrent selection for increased or decreased crossing over in Zea mays L. 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 [C ₃LR]) were evaluated. The mean recombination frequency changes between C₀ and C₃HR are significant at all chromosome regions (su1-c2, +5%; a2-pr1, +24%; sh1-wx1, +8%). The mean recombination frequency changes between C₀ and C₃LR are significant at the chromosome 4 (su1-c2,-15%) and 5 (a2-pr1,-27%) linkage groups. The mean recombination frequency did not change significantly from C₀ to C₃LR at either of the chromosome 9 regions. Compared to the C ₀ population, the sum of the genetic distances at these chromosome regions increased 9.5% in the C₃HR population and decreased 14.9% in the C₃LR population. Selection for high or low recombination frequency successfully modified recombination frequency.