A comparison of several procedures for mass selection in winter rye. II. What are the merits of adjusting phenotypic values?

Summary To get an improved impression of the genotypic value of individual plants the literature suggests to adjust their phenotypic values according to a moving mean correction or by means of an analysis of covariance, where the mean phenotypic value calculated across neighbours is used as the concomitant variable. In the present paper it is shown that the theoretical merits of these adjustments are promising: they eliminate the contribution due to the trend in soil fertility from the phenotypic value. In an experimental verification actual merits did, however, not show up.It is concluded that interplant competition is the main cause for the failure of the studied adjustments. These may be effective in virtual absence of intergenotypic competition. Thus, in case of single plant selection an extremely low plant density would be required, whereas selection among lines or families would require evaluation by means of multi-row plots.