The Convergent Improvement of Selfed Lines of Corn

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Abstract
The need of a method for improving the productiveness of selfed lines of corn without interfering with their behavior in hybrid combination is pointed out, and the principle of convergent improvement is suggested as meeting this need. This involves the reciprocal addition to each of 2 homozygous selfed lines, which combine to produce a high-yielding cross, of those dominant favorable factors which one line lacks, but which are carried by the other, by: (1) crossing the 2 lines; (2) back-pollinating to 1 line through each of several generations to recover the genotype of the recurrent parent; (3) at the same time practicing selection to retain fa''vorable factors entering the cross from the other parent; (4) selecting within selfed lines to fix the added factors in the homozygous condition; (5) performing, these operations in parallel with each of the original iines as the recurrent parent; and (6) repeating the operation to achieve further improvement, using the recovered lines in place of the original parent lines as foundation stocks. The quantitative relations of the factors under different assumptions are considered, and the bearing of experiments with convergent improvement upon certain theoretical principles is discussed. Such experiments would be of special interest in connection with studies of hybrid vigor, and should provide a basis for critical experiments in differentiating between the action of dominant favorable factors and possible physiologic stimulation due to unlike germ plasm within the cells.

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