Three Cycles of Recurrent Selection for Altered Recombination Frequency in Zea mays.

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 all five chromosome regions of the three linkage groups. Population effect was highly significant for all five chromosome regions with populations derived following selection for high or low RF on these chromosomes producing individuals exhibiting high or low RF, respectively. The mean RF difference between C0 and C3HR, C3HR and C3LR are significant at all five chromosome regions. The mean RF difference between C0 and C3LR are significant at all chromosome regions on linkage group 4 and 5. The mean RF of C0 was high than that of C3LR at each of the chromosome region on linkage group 9, but it was not significant. From the above results we conclude that modification by selection for high or low RF has been successful.