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SUMMARYFour selection experiments were sown: single-row plots with single row-spacing (:::: 20 em), single-row plots with double row spacing (:::: 40 em), three-row plots and six-row plots both with single row-spacing (:::: 20 em). Selection entries were mimiced by 16 different varieties or advanced breeding lines, which were also sown in a yield trial. Each experiment was laid out as a 4-times replicated randomized block design. Row length was 2 m. Alley borders and border-rows of multiple-row plots were harvested separately to evaluate the effects of different harvesting procedures on the selection efficiency. Removal of alley borders was found to be disadvantageous, since the gain in precision was more than offset by the loss in sampled area. Wide spacing of single-row plots improved the selection efficiency in comparison with normal spaced single-row plots. In multiple-row plots the selection efficiency was not improved by harvesting only the central rows.For gross plot yield ( = yield of net plot + yield of alley borders) the differences in selection efficiency between the various selection plot-types were explained on the basis of the genetic variance, the environmental variance and the coefficient of genetic correlation with 'farm' yield as determined in the yield trial.

INDEX WORDSTriticum aestivum, wheat, growth analysis, relative growth rate, selection. SUMMARYFor a better insight in the effect of wide spacing on the outcome of plant selection in spring wheat, the growth of free-grown individual plants was followed in time for each of 12 cultivars. As time proceeded, the cultivar differences for per-plant weight showed progressively less relation with those for seedling weight. At anthesis, the genetic correlation with seedling weight was still about 0.80, but at final harvest it was only 0.06. This contrasted with the genetic correlation between seedling weight and final biomass in closely planted mixtures which was on the average 0.77. The outcome of selection of genotypes in isolation is therefore expected to deviate substantially from that of selection in densely planted segregating populations where the differences in initial size tend to be maintained in time.The ranking of the varieties grown in isolation changed in time because of differences in relative growth rate (RGR). The genetic variance of RGR decreased much less with time than RGR itself. Late-flowering varieties showed the higher RGR so that these varieties improved their position in the ranking in isolation.Special attention is paid to the methodology of plant growth analysis in variety experiments and in estimating means and variances of RG R.