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Marker Effects Estimated from Testcrosses of Early and Late Generations of Inbreeding in Maize

Asgrow Seed Company, 634 Lincolnway, Ames, IA 50010
Univ. of Illinois, S112 Turner Hall, 1102 South Goodwin Ave., Urbana, IL 61801
ICI Seeds, 2369 330th Street, Slater, IA 50244

^* Corresponding author (email jdudley{at}uiuc.edu).

In maize (Zea mays L.) breeding programs, early generation testing allows the discarding of lines with poor combining ability early in the inbreeding process. Molecular markers can be used to locate quantitative trait loci (QTL) and measure marker effects in early generations. For marker assisted selection to be useful in improving the efficiency of early generation testing, marker effects estimated in early generations must agree with marker effects in later generations. However, limited attention has been given to comparing marker effects in different generations of the same cross. Therefore, the overall objective of this research was to compare marker effects estimated from testcross performance of 190 S₁ and S₄:S₅ lines from a maize population (BSll(FR)C7) by inbred (FRMo17) cross. A total of 146 probe-enzyme combinations were used. To be most useful, correlations between marker effects in different generations need to be higher than phenotypic correlations. For all traits, phenotypic correlations were less than genetic correlations that were less than correlations based on marker effects estimated for the best set of markers from the S₁. Except for grain yield, test weight, and days to anthesis, the correlations based on all marker effects were higher than the genetic correlations. As an example, the phenotypic correlation for grain yield was 0.36, the genetic correlation was 0.60, the correlation using all markers was 0.50, and that for the best set of markers was 0.86. Overall, marker effects estimated in S₁ and S₄:S₅ testcrosses had reasonable agreement. Thus, marker information from early generations should improve the prediction of later generation performance.

Received for publication January 6, 1996.

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