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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #118196
Title: THE HARDY-WEINBERG AND LINKAGE EQUILIBRIUM STATUS OF BSSS AND BSCB1 MAIZE POPULATIONS

Author
item LABATE, JOANNE - CORNELL UNIVERSITY
item Lamkey, Kendall
item LEE, MICHAEL - IOWA STATE UNIVERSITY
item WOODMAN, WENDY - IOWA STATE UNIVERSITY

Submitted to: Maydica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Corn is cross-pollinated by wind, which is why we refer to the varieties grown by farmers prior to 1930 as open-pollinated varieties. They are freely pollinated by pollen that happens to be in the air. The source of the pollen can be controlled by isolating the variety from other varieties by distance or by artificially simulating cross-pollination by making pollinations under controlled conditions by hand. The latter method (hand pollination) is predominately used by corn breeders and germplasm curators to multiply seed stocks for storage. By using molecular markers, we found that hand pollination is a very close approximation to what happens naturally when corn is wind pollinated. This research will be of benefit to germplasm curators who can use it to confident that their pollination methods are adequate to maintain the integrity of the open-pollinated varieties they are charged to maintain. Plant breeders and theoretical geneticist will also find this research to be of interest because one of the underlying assumptions of genetic models is that corn plants are pollinated randomly by the available pollen pool.

Technical Abstract: Because maize is an annual species those working with it must frequently make crosses to preserve and maintain populations. Random mating is performed either using hand-pollination techniques or in wind-pollinated isolated blocks. Eight two restriction fragment length polymorphism (RFLP) markers were used to examine samples of random mated, hand-pollinated BSSS(R) and BSCB1(R) maize populations to find out whether their genotypic proportions conformed to predicted outcomes of random mating. The majority of loci conformed to expectations for Hardy-Weinberg equilibrium (HWE). Excess homozygosity was observed at 87% of the loci where the null hypothesis of HWE was rejected. For pairs of polymorphic loci, linkage equilibrium was observed in the BSSS(R) and BSCB1(R) progenitor populations (fewer than 5% of all tests rejected the null hypothesis of equilibrium at the P d 0.05 significance level). The BSSS(R)C0, BSCB1(R)C0 and BSCB1(R)C12 2populations showed slight increases in the proportion of pairs of loci in linkage disequilibrium compared to the progenitors (approximately 8.4% of all pairs of loci rejected the null hypothesis at the P d 0.05 significance level). BSSS(R)C12 was an extreme outlier with 25.0% of all pairs of polymorphic loci displaying significant (P d 0.05) linkage disequilibrium. This result was likely caused by the artificial grouping of three BSSS(R)C0 plants with 97 BSSS(R)C12 plants during sampling. Results from principal components analysis of all individuals based on RFLP alleles supported this interpretation. Overall, most of the observed deviations from equilibrium were likely to have been caused by positive assortative mating in the case of HWE, and natural selection for epistatic effects between unlinked loci in the case of linkage disequilirium.