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Backcrossing and Intermating in an Exotic x Adapted Cross of Maize

Pioneer Hi-Bred Intl., Inc., 590 Deer Rd., Macomb, IL 61455
Pioneer Hi-Bred Intl., Inc., P.O. Box 1004, Johnston, IA 50131
Geadelmann, Holden's Foundation Seed, R.R. #1, Box 112, Stanton, MN 55018

R. H. Peterson and D. D. Stuthman

Dep. of Agronomy and Plant Genetics, Univ. of Minesota, St. Paul, MN 55108

^* Corresponding author (hoffbeckmd{at}phibred.com).

Incorporation of exotic germplasm into the U.S. maize (Zea mays L.) germplasm pool has often been proposed. Backcrossing and intermating were studied as techniques for incorporation of exotic germplasm using the populations AS-A and MN-ETO. Three levels of backcrossing (0, 1, and 2 backcrosses) and cycles of intermating (1, 3, and 5 cycles) were examined in all combinations by extracting 100 random S₁ lines from each treatment for field evaluation. All lines were evaluated for eight traits in six environments. Data for grain yield, grain harvest moisture, lodging, plant height, ear height, number of days to 50% silk emergence, number of days to 50% pollen shed, and a selection index (SI) [SI = grain yield (kg ha^–1) –18.8 x harvest moisture (g kg^–1)] were analyzed. Analyses on trait means, genetic variances, correlated responses, selection differentials, and frequency distributions indicated that backcrossing generally shifted means and resulted in smaller genetic variances. Phenotypic correlations were both increased and decreased depending on the comparison examined. Changes of selection differentials of secondary traits were consistent with phenotypic correlations. The effect of backcrossing on the means of selected and unselected lines was very similar. Many changes were maturity related. Intermating levels used had no detectable effect on the populations. Significant differences were found, but these were isolated and did not form trends across intermating levels or backcross treatments. The results of this study suggest that backcrossing is useful in the incorporation of exotic germplasm, but results do not support the use of repeated intermating.

Received for publication March 23, 1994.

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