Changes in relative growth rate with plant ontogeny in spring wheat genotypes grown as isolated plants

Summary For 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 RGR.