Response to S1 and testcross selection in corn (Zea mays L.)

Many different selection schemes are available for the genetic improvement of corn (Zea mays L.). This study was conducted to compare and testcross (TC) recurrent selection for the improvement of grain yield in Tennessee late low-ear (TLLE) synthetic. TLLE had undergone ten cycles of mass selection for low ear height prior to the initiation of selection for grain yield. Four cycles (C) of S₁ and TC selection procedures were completed, resulting in nine populations for evaluation; i.e. C0; C1, C2, C3, and C4 of S₁selection; and C1, C2, C3, and C4 of TC selection. Each of these cycle populations were evaluated as random mated, selfed (except C4) , and hybrid populations. Hybrids were produced by crossing each of the cycle populations onto T224 X T232 and K55 X CI66. The three groups were grown as separate experiments in 1987 and 1988 at Knoxville and Crossville, Tennessee.

In random mated populations, S₁ selection increased grain yield 11% per cycle, while TC selection resulted in a 7% gain per cycle. In tests of selfed populations S₁ and TC selection resulted in 17% and 12% increases per cycle, respectively, at Knoxville. No selected cycles differed from CO at Crossville in tests as selfed populations. Hybrids produced by crossing cycles of selection onto T224 X T232 showed little response to selection for either method. In crosses onto K55 X CI66 at Knoxville, S₁ selection and TC selection increased grain yield 5% and 6% per cycle, respectively. At Crossville, S₁ selection and TC selection increased yield 9% and 11% per cycle, respectively.