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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #70563
Title: MOLECULAR GENETIC DIVERSITY AFTER RECIPROCAL RECURRENT SELECTION IN BSSS AND BSCB1 MAIZE POPULATIONS

Author
item LABATE, JOANNE
item LAMKEY, KENDALL
item LEE, MICHAEL - ISU
item WOODMAN, WENDY

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The success of improving corn depends on selecting individuals of high quality from genetically diverse corn populations and interbreeding them. It is important for breeders to understand how much genetic variation exists in corn populations, and how fast it becomes depleted over many generations of selection, so they can design effective breeding programs. We obtained genetic data from several-hundred individual plants representing populations both before and after strong selection for increased yield. We found a large decrease in genetic variation in populations after selection, and have gained a greater comprehension of how to predict the rate of this decrease. Our findings are relevant to breeders of corn and other crops by relaying to them a more thorough understanding of the genetic outcomes of breeding. This should help breeders improve existing programs and suggest strategies with which they can design new programs, in order to continue to rapidly advance in crop improvement.

Technical Abstract: Iowa Stiff Stalk Synthetic (BSSS) and Iowa corn borer Synthetic #1 (BSCB1) are undergoing reciprocal recurrent selection as part of Iowa's Federal-State maize (Zea mays L.) breeding program. An evaluation of molecular genetic changes in the populations, interpreted within the context of directional selection and genetic drift, will aid in understanding the continuing success of this program. It may also suggest methods for improvements in this or other programs. This study focuses on molecular genetic variation in BSSS(R) and BSCB1(R) cycle 0 (CO) and cycle (C12) populations, as well as the inbred progenitors (P) used to synthesize BSSS and BSCB1. Multilocus genotypic data for 82 restriction fragment length polymorphism (RFLP) loci were collected from 100 randomly sampled individuals from each CO and C12 population, 16 BSSS(R) progenitors, and 12 BSCB1(R) progenitors. Progenitor lines were highly homozygous as expected. No single progenitor seems to have made excessive genetic contributions to CO or C12. It was found that the BSSS and BSCB1 progenitor populations were initially genetically similar (Nei's genetic distance = 0.07). After 12 cycles of selection, they have substantially diverged (Nei's distance = 0.66). The genetic base across progenitor populations was very broad and continues to be so at C12 (0.6). Within both populations, polymorphism has decreased from about 99% to 75%, and gene diversity has decreased from about 0.6 to 0.3 between P and C12. The mean number of alleles has dropped from about four to less than three. Assuming an effective population size as the mean number of selected S1 lines over 12 cycles, the observed loss of variation is consistent with theoretical expectations resulting from genetic drift of neutral alleles.