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Testcross Evaluation of F₂ Populations from Maize Inbreds selected for Unique Favorable Alleles

Ciba-Geigy Semences, 29 rue de la Croix Des Bois, 49800 Brain-Sur LAuthion, France
Dep. of Agronomy, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana IL 61801

^* Corresponding author.

A method has been developed to identify donor inbreds with favorable alleles not present in an elite hybrid. Evaluation of the method requires comparison of performance of progenies from lines identified as having high numbers of favorable alleles with those from lines having a low number. The objective of this study was to compare testcrosses of F₂ plants from crosses of an elite line with donor lines selected for high estimates with those of F₂ plants from crosses of an elite line with donor lines having low estimates of favorable dominant alleles not present in the elite hybrid. For the improvement of maize (Zea mays L.) hybrids B73 x Mo17 and B73 x B77 donor lines derived from Stiff Stalk Synthetic, Lancaster, and other sources with low and high estimates of the relative number of favorable dominant alleles for grain yield not present in the elite hybrids were selected. Testcrosses of randomly chosen F₂ plants from the cross between selected donor inbreds and parental lines were evaluated at two locations in 1986. The F₂ testcross populations developed from inbreds with large estimated number of favorable alleles had on the average more testcrosses genetically superior to the check mean than those from inbreds with low estimates. Changes of the F₂ population mean compared to the check mean and the expected variability among testcrosses could be predicted. These predictions were reliable for traits where favorable alleles were either dominant or recessive. Methods were developed to estimate the total number of loci segregating (n) in the testcrosses and the average difference between homozygotes (µ).

Received for publication March 18, 1988.