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Five Cycles of Replicated S₁ vs. Reciprocal Full-Sib Index Selection in Maize

Kenya Agric. Res. Inst., P.O. Box 57811, Nairobi, Kenya
Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583-0915

^* Corresponding author.

Five cycles of S₁ per se (S₁) and reciprocal full-sib (RFS) selection were compared for the improvement of three maize (zea mays L.) populations and two population crosses. The replicated structure of the selection experiments allowed direct comparisons of selection methods together with measures of genetic drift. The selection criterion used was a multiplicative index involving yield, moisture, upright plants, and undropped ears and therefore the experiment measures the value of this type of index in selection studies. Populations and population crosses evaluated were Nebraska B. Synthetic (NBS), Nebraska Stiff Stalk Synthetic (NSS), Nebraska Krug open pollinated variety (NKS), NBS x NSS, and NBS x NKS. Improvement was measured in random mated, bulked inbred (S₁) populations, and the population crosses. Both selection procedures were performed in three replicates. The entries for the evaluation study were derived from Cycle 0 and recombined replicate populations from Cycles 3 and 5. The evaluation trials were grown in 1985 and 1986 at Lincoln, NE. The S₁ selection increased index values in the bulked inbred populations by 5.8% per cycle when averaged over populations. The RFS selection increased index values of inbred populations by 3.4% per cycle. Both methods were equally effective in improving index values of the random mated populations with average responses of 2.0% for S₁ and 1.8% for RFS selection per cycle. The average index response in the population crosses was 3.6 and 2.9% per cycle for RFS and S₁ selection, respectively. Genetic drift was observed to cause significant differences among the replicate populations for index and its components.

Received for publication January 12, 1988.