|Holland, Jim - Jim|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2003
Publication Date: 11/3/2003
Citation: Tarter, J.A., Goodman, M.M., Holland, J.B. 2003. Testcross performance of semiexotic inbred lines derived from latin american maize accessions.. Crop Science. Interpretive Summary: Genetic diversity of commercial maize (Zea mays L.) in the United States is limited, leaving the crop vulnerable to new biotic and abiotic stresses, and limiting the potential for long-term gains in productivity. Tropical maize is a valuable genetic resource that can be used to broaden the geneteic base of U.S. maize. Tapping this resource is difficult, however, because tropical maize is unadapted to most U.S. maize production environments. We report the results of a long-term (20 years) program designed to adapt superior Latin American maize landrace populations to U.S. growing conditions. Better tropical maize populations were crossed to inbred Mo44, and after ten years of selection, a set of 164 inbred lines was created from these crosses. The lines are called semiexotic because half of their pedigree is an exotic landrace and the other half is a U.S. inbred line. The semiexotic lines wee crossed to a standard Corn Belt Dent hybrid to create 164 hybrids for yield trials. We found that 33 hybrids created from semiexotic lines yielded better than the hybrid created from their original U.S. patent, Mo44. In addition, the hybrids created from semiexotic lines were generally well-adapted to U.S. growing conditions: they flower at appropriate times, their grain moisture at harvest is acceptable, they are not too tall, and they remain standing until harvest. These new hybrids are not competitive with commercial U.S. hybrids for grain yield, but the semiexotic lines will serve as valuable donors of favorable alleles to future U.S. hybrids.
Technical Abstract: Genetic diversity of commercial maize (Zea mays L.) in the United States is limited. Tropical maize represents the most diverse readily available source of germplasm with which to broaden the genetic base of temperate maize. One hundred sisty-four inbred lines were developed from crosses between temperate-adapted inbred line Mo44 and 23 Latin American maize accessions. The objectives of this study were to compare the combining ability of these semiexotic inbred lines to the combining ability of their temperate parent M044, and to compare semiexotic line testcrosses to commercial checks. Mo44 and each semiexotic line were testcrossed to temperate hybrid LH132' LH51 for evaluations. In preliminary replicated yield trials in seven environments, testcrosses of 33 semiexotic lines, representing six different races, had significantly greater grain yields than the Mo44 testcross. Advanced yield evaluations were performed on check entries and 33 selected semiexotic line testcrosses in three additional environments. Across ten environments, 12 semiexotic lines exhibited significantly greater grain yield than Mo44 in testcrosses, indicating recovery of favorable exotic alleles. Semiexotic testcrosses were not competitive with commercial hybrids for grain yield, but were similar to or better than commercial hybrids for other agronomic characters, such as grain moisture and flowering time. Many of the superior accessions represent relatively recent introductions into the regions from which they were collected. Tropical landraces appear to be a useful source of exotic germplasm that can be used to simultaneously broaden the genetic base of modern U.S. corn production and improve productivity.