Comparison of Three Types of Testers for the Evaluation of Inbred Lines of Corn 1

THE practical phase of corn breeding is based upon the development of inbred lines and the evaluation of these lines in hybrid combinations. Performance of inbred lines per se does not provide an entirely adequate measure of their value in hybrid combinations. Therefore, the development of simple and adequate methods of testing new lines has been a major problem in the development of new hybrids. In the period from 1920 to 1930, the customary procedure was to make and test the n(n—1)/2 combinations which are possible among a set of n lines. As the number of lines increases, the amount of material to be grown and compared in yield trials soon becomes prohibitive. This difficulty led to the introduction and general adoption of the top cross test for the preliminary evaluation of new lines. Since the adoption of the top cross test, a number of studies dealing with choice of testers have been reported. These have served to clarify the general problem of "testers' but have not provided satisfactory answers to all of the problems. A desirable tester may be defined as one that combines the greatest simplicity in use with the maximum information on the performance to be expected from the tested lines when used in other combinations or grown in other environments. No single tester can completely fulfill these requirements. The choice of a tester is determined to a considerable extent upon the expected use for a particular group of lines. If these are destined as replacements for lines in existing hybrid combinations, the tester chosen will certainly differ from that selected if the lines are to be screened for average performance and the survivors tested