The combined effects of dominance and inbreeding on covariances between relatives are still poorly understood in maize (Zea mays L.) populations. Our objectives were to address the following questions: (i) What is the importance of dominance in a maize synthetic? (ii) How does inbreeding affect the genetic variance among individuals in a maize synthetic. (iii) How do the covariance parameters compare between populations? (iv) How does breeding design impact estimators? We estimated covariance components for inbred relatives in the maize synthetic BSCB1(R)C13. Previous estimates of covariance parameters have been used to explain the ineffectiveness of inbred progeny selection in the stiff‐stalk population BS13. We found that the dominance variance was larger than the additive variance for grain yield, whereas the additive variance was larger than the dominance variance for all other traits. Negative estimates of the covariance between additive and homozygous dominance deviations were found for all traits with the exception of traits associated with reproductive maturity, suggesting a negative relationship between inbred and outbred performance. The correlation between genotypic values and breeding values was lower for grain yield than for any other trait. Our results were similar to previous results found in the stiff‐stalk maize population BS13, suggesting similarity in structure among populations.

Historically, inbred progeny selection has been promoted as an effective means of improving both inbred and outbred performance, and in some cases as being superior to other methods. Advances in theory and new estimates of genotypic covariance components have allowed us to make better predictions of gain from inbred progeny selection than previously available. We developed predicted gain equations using a full model, based on new theory and estimates, and a reduced model, which contained only the additive genetic variance in the numerator, for three maize (Zea mays L.) populations, BS13(S)C0, BSCB1(R)C13, and 3L Comp (HS‐S1)S1 Outbred progeny selection was superior to inbred progeny selection for plant height and grain yield when the response unit was the outbred population. Inbred progeny selection was superior for plant height in both populations and more effective for grain yield in BS13(S)C0 in inbred response units. Negative estimates of the covariance parameter D1 reduced predicted gain for inbred progeny selection in the full model in comparison to the reduced model when D1 was ignored.

When beef cattle (Bos taurus) are fed grain of maize (Zea mays L.) in which the concentration of phosphorus (P) exceeds the animal's need for this element, the excess P is excreted in the feces. Spreading this manure on cropland increases the potential for P pollution of surface waters by run‐off. Experiments were undertaken to determine the relative magnitudes of genotypic and nongenotypic variances of P concentration in maize grain (P‐Gr) to assess the ability to select maize genotypes in which this trait more closely matches the dietary need of beef cattle. Genetic variability was found in a population developed from a cross of Illinois High Protein (IHP) × Illinois Low Protein (ILP). Because of few low P‐Gr segregates, the IHP × ILP population was not considered a good breeding source for this trait. Nongenetic sources of variance were significant but small compared with genotypic variances. Broad‐sense heritability (H) for P‐Gr among S1 family means in the IHP × ILP population was estimated at 0.82. This high value suggested that this trait would respond to selection. A comparison of mean values of S1 families selected on the basis of performance in 2000 or in 2001 alone to those selected on the basis of 2‐yr data suggested that the loss in efficiency resulting from selecting on 1‐yr data would be only approximately 5%.

to feedlot rations of beef cattle, have P concentrations that are at least two to four times as high as in whole When beef cattle (Bos taurus) are fed grain of maize (Zea mays grain (Milton, 2000). The National Research Council L.) in which the concentration of phosphorus (P) exceeds the animal's (1996) recommended a P intake by beef cattle of 0.20 need for this element, the excess P is excreted in the feces. Spreading this manure on cropland increases the potential for P pollution of to 0.30% P, assuming a daily feed intake of 9 to 11 kg. surface waters by runoff. Experiments were undertaken to determine However, Erickson et al. (1999) found that the P rethe relative magnitudes of genotypic and nongenotypic variances of quirement of finishing yearlings was 0.14% or less. P concentration in maize grain (P-Gr) to assess the ability to select Other feeding trials indicated that the National Remaize genotypes in which this trait more closely matches the dietary search Council guidelines over-predicted by at least need of beef cattle. Genetic variability was found in a population 25% the need of yearlings (Erickson et al., 2002) and developed from a cross of Illinois High Protein (IHP) ϫ Illinois Low of developing heifers (Call et al., 1978) for P. Protein (ILP). Because of few low P-Gr segregates, the IHP ϫ ILP Excess amounts of P that are ingested by cattle are population was not considered a good breeding source for this trait. excreted largely in the feces. When manure from feed-Nongenetic sources of variance were significant but small compared lots is continually spread on adjacent cropland, levels with genotypic variances. Broad-sense heritability (H) for P-Gr among S 1 family means in the IHP ϫ ILP population was estimated of P in the soil often become much higher than needed at 0.82. This high value suggested that this trait would respond to for crop production. Runoff from soils that are high in selection. A comparison of mean values of S 1 families selected on the P is a major cause of eutrophication in surface waters basis of performance in 2000 or in 2001 alone to those selected on (Duda and Finan, 1983). Traditionally, application rates the basis of 2-yr data suggested that the loss in efficiency resulting for cattle manure on cropland have been calculated by from selecting on 1-yr data would be only approximately 5%. matching the nitrogen content of the manure to the nitrogen requirement of the intended crop, which often is maize. Maize plants use nitrogen and phosphorus in

No abstract