Performance of Testcross Hybrids of Semi-exotic Inbred Lines Contained Different Proportions of U.S. Corn Belt Germplasm

Abstract

U.S. Corn Belt germplasm including 8 hybrids, 5 open pollinated varieties, 5 BSSS and 4 non-BSSS inbred lines were introduced and subsequently crossed and backcrossed to 6 tropical inbred lines namely Nei9008, Nei9202, AMATLC0HS 63-2-5-E-3-1-2, AMATLC0HS 170-2-3-2-1-1-1-B-3, Ag18
and Ki42 to adjust the proportion of exotic germplasm to 50 and 25 % of each of the tropical lines. Semiexotic inbred lines were extracted from the 48 groups of adjusted exotic germplasm (6 tropical lines X 4 exotic groups X 2 exotic proportions). Subsequently, the resulted 48 BC₀S₃ and 48 BC₁S₂ were crossed to 2 tropical inbred testers, Ag20 (high general combining ability) and Ag29 (high specific combining ability). The experimental results revealed that the hybrids were the most promising exotic sources for desirable alleles followed by non-BSSS inbred lines and OPV’s, respectively. In addition, 25% exotic inbred lines performed better than the 50% exotic inbred lines in combinations with the 2 testers. Testcross hybrids of Ag20 out performed the testcross hybrids of Ag29. All top-10 testcross hybrids were derived from crosses involving with Ag20. The top-6 testcross hybrids which yielded statistically non-significant differences from the best tropical hybrid check were derived from semi-exotic inbred lines involving with
each of the 6 tropical recurrent inbred lines with donor parents from exotic hybrids and non-BSSS inbred lines, except one combination from BSSS inbred lines. The results suggested that highly improved hybrids and inbred lines were the most promising exotic sources. Different testers gave different results and therefore, the best testers should be the intended inbred counterpart in the new hybrid combinations or otherwise the appropriate method should be selection for performance per se of inbred lines followed by diallel cross of selected lines.