|Holland, Jim - Jim|
Submitted to: Maydica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2004
Publication Date: 5/10/2006
Citation: Tarter, J.A., Holland, J.B. 2006. Gains from selection during the development of superior semiexotic inbred lines from latin american maize accessions. Maydica. Interpretive Summary: The genetic base of the U.S. corn crop is narrow. Current hybrids were developed from only a small sample of the available genetic diversity in the species. Tropical maize, primarily from Latin America, is a useful resource for U.S. corn breeding programs because it is genetically diverse. However, tropical maize is poorly adapted to U.S. growing conditions. A 30-year program has been underway in North Carolina to identify superior tropical germplasm sources and adapt them to temperate growing conditions. We tested populations and lines representing different stages of selection during this long term program in an attempt to document the amount of gain from selection that has occurred and to determine which stages of selection were most effective. Results indicate that inbred lines developed from this program produce much better hybrids in combination with U.S. corn than the original tropical sources did. Most of the gains were achieved in the first few generations of selection for general adaptation to U.S. growing conditions.
Technical Abstract: Tropical maize represents the most readily accessible source of genetic diversity within the species but is unadapted to temperate production environments and thus not utilized on a large scale. M.M. Goodman has conducted a program to incorporate tropical landrace germplasm into the U.S. Corn Belt Dent gene pool for more than 30 years. During that time, about 1300 Latin American maize accessions underwent seven different stages of selection and breeding and resulted in 25 semiexotic inbred lines with superior testcross performance. Selection stages included: 1) selection for photoperiod insensitivity in populations derived from crosses between accessions and temperate inbred line Mo44, 2) testcross selection of noninbred semiexotic populations and 3) selection during inbreeding generations. To test the effects of the different stages of selection on agronomic performance, we evaluated 25 selected semiexotic lines, and their 12 progenitor tropical maize accessions, and 47 noninbred semiexotic families resulting from three cycles of recurrent phenotypic selection for photoperiod insensitivity in populations derived from the same 12 accessions (C3 families). Each experimental entry was testcrossed to LH132 ' LH51 and testcrosses were evaluated in eight North Carolina environments. Significant agronomic improvement was observed for grain yield, grain moisture, flowering time, ear and plant heights, lodging resistance and smut (Ustilago zeae (Beckm.) Unger) resistance when comparing mean C3 family testcross performance to the mean original accession testcross performance, but no additional improvement was observed in the inbred testcrosses. This implies that most gains in testcross performance occurred during the early generations of phenotypic selection for general adaptation. Selection during later inbreeding generations may have resulted in improved inbred per se performance, but did not result in improved testcross performance.