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CROP BREEDING, GENETICS & CYTOLOGY

Genetic Variation in Maize Breeding Populations with Different Numbers of Parents

Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, 411 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108-6026

^* Corresponding author (bernardo{at}umn.edu)

The development of breeding populations from two related inbreds restricts the amount of variability expected in the cross. Our objective was to determine if, as expected from an additive genetic model, genetic variance in maize (Zea mays L.) decreases as the number of parents of the population decreases. Eight random F₂ plants derived from the same single cross were selected as parents and were selfed to form F₃ families. These F₃ families were intermated in a hierarchical manner to form populations with N = 1, 2, 4, or 8 parents. Testcross families were evaluated in four Minnesota environments in 2003. Marker heterozygosity at 62 simple sequence repeat loci decreased with N and had a near-linear association with expected heterozygosity. Testcross genetic variance (V_TC) generally decreased with N, although differences observed at N = 2, 4, and 8 were mostly insignificant. For grain yield, V_TC was significantly higher at N = 4 than at N = 2. The V_TC for grain yield at N = 4 was slightly higher than the estimate of V_TC in the base population, strongly indicating a genetic variance in excess of what is predicted by an additive genetic model for a small population. Differences in testcross means were likewise inconsistent with an additive genetic model. The results imply that nonadditive gene effects in elite maize inbreds help maintain genetic variance in small populations and that using multiple parents may help sustain genetic variability in advanced cycle breeding.

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