Doubled-haploid breeding systems are typically based on sampling gametes from F, plants. However, in the case of repulsion linkages, additional recombination could be advantageous. Pre-selection of gamete donors might also shift progeny performance in a desired direction. The objectives of this study were to quantify the effects of an additional round of recombination and assess the effectiveness of preanthesis selection in the production of barley doubled haploids. Assessments were conducted on: 1. 100 F,-derived lines representing a subset of lines used in previous genome-mapping studies; 2. 100 random Fjderived lines; and 3. 50 F2-derived lines from gamete donors selected for early heading. An additional round of recombination had only a modest effect on generating more favourable genotypes. Pre-anthesis selection was ineffective in generating an earlier heading population. According to pubHshed quantitative-trait locus (QTL) analyses based on the F|-derived population, there are few repulsion linkages between QTL determining the traits measured in this experiment. Any advantages to be gained from postponing the generation of derivation of doubled haploids must be weighed against the delay and additional cost.

Hill plots offer advantages in testing large germplasm arrays with limited area and seed. However, the relationship of trait expression between hill vs. row plots remains in question. The development of quantitativetrait-locus (QTL) analysis offers alternative methods of testing hypotheses regarding levels of coincident gene effects in divergent plots. The objective of this study was to compare hill and row plots in terms of QTL detection, number of common QTLs and plot-type-specific QTLs for various characters in barley. Assessments were based on sets of 100 F,-derived doubled haploid progeny from two environments of hillplot data and two sets of multiple-environment row-plot data. Common large-effect QTLs for height, heading date, and 1000-kernel weight were detected in both plot types. Fewer QTLs were detected in the hill-plot data, with only one QTL detected for grain yield. There were no hillplot-specific QTL effects. Hill plots appear to be best suited to highly heritable characters such as height, heading date, and 1000-kernel weight. Evaluation of grain yield is best deferred until larger experimental units can be employed.Key words: Hordeum vulgare -quantitative trait locusdoubled haploids -hill plots Hill plots are an attractive phenotype assessment option for small-grain germplasm when there are large germplasm arrays and limited seed and/or land (McFerson and Frey 1990). The underlying issue, of course, is the level of coincident trait expression between hill and row plots. In general, there is a consensus that hill plots provide effective discrimination for highly heritable traits, such as maturity and plant height, but there is considerable disagreement as to their effectiveness for traits such as grain yield. The issue is not easily addressed from an experimental standpoint. An advantage of hill plots is that their limited spatial requirements minimize field heterogeneity when large numbers of lines are evaluated. However, in an empirical comparison of row vs. hill plots, the number of entries must be minimized in order not to unduly bias the performance of the row plots.Despite the variety of test statistics employed in comparing data frotn adjacent hill and row plot experiments -the nurnber of lines in common at given selection intensities (Tragoonrung et al. 1990), correlations of various sorts (St. Martin et al. 1990) and coefficients of variation (Pfelffer and Pilcher, 1989) ^ there is still no consensus as to the relative merits of the two plot types. The recent development of medium-density genome-mapping techniques has allowed for estimation of the chromosome location of genes underlying quantitative phenotypes. Quantitative-trait loci (QTLs) for a range of agronomic and maltingquahty traits in barley were described by Hayes et al. (1993), based on the medium-density map reported by Kleinhofs et al. (1993). Hayes et al. (1993) employed conservative criteria for identifying QTL peaks and support intervals for average performance in multiple environments, based on the rationale that chromoso...