|Holland, Jim - Jim|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2004
Publication Date: 8/1/2004
Citation: Tarter, J.A., Goodman, M.M., Holland, J.B. 2004. Recovery of exotic alleles in semiexotic maize inbreds derived from crosses between latin american accessions and a temperate line.. Theoretical and Applied Genetics. 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 genetic base of U.S. maize. Tapping this resource is difficult, however, because tropical maize is unadapted to most U.S. maize production environments. In order to adapt such germplasm to U.S. growing conditions, we need to cross them to adapted lines or hybrids and select for good-performing progeny. A potential problem with this approach is that, during selection, one may lose a substantial proportion of the exotic genes, making the breeding process pointless. To determine how much tropical-derived germplasm remains in inbred lines derived from such a process, we used DNA fingerprinting techniques on 161 semiexotic lines derived from crosses between superior Latin American maize landrace populations and a U.S. inbred line. We found that, at minimum, an average of 31% of the genes in these lines derived from their tropical parent, indicating that a substantial proportion of exotic genes survive in semiexotic lines even following strong selection for adaptation to U.S. growing conditions. We also found that lines with higher proportions of exotic germplasm were not necessarily higher or lower-yielding than lines with less exotic germplasm. Some of the lines had significantly higher yields than their temperate parent, indicating that some of their tropical alleles contributed to increased yields.
Technical Abstract: Genetic diversity of elite maize germplasm in the United States is narrow relative to the species worldwide. Tropical maize represents the most diverse source of germplasm. To incorporate germplasm from tropical maize landraces into the temperate gene pool, 23 Latin American maize accessions were crossed to temperate inbred line Mo44. During inbred line development, selection was practiced in temperate environments, potentially resulting in the loss of substantial proportions of tropical alleles. Genotyping 161 semiexotic inbreds at 51 SSR loci permitted the classification of the alleles as either Mo44 or tropical in origin and allowed for the estimation of the proportion of detectable tropical alleles. On average, the percentage of detectable tropical alleles ranged among lines from 15% to 56%, with a mean of 31%. These are conservative, lower-bound estimates of the proportion of tropical germplasm within lines because it is not known how frequently Mo44 and the tropical maize accession parental populations have the same SSR alleles. These results suggest that substantial proportions of exotic germplasm were recovered in the semiexotic lines, despite their selection in temperate environments. The percent of tropical germplasm in semiexotic lines was not correlated to the grain yield or moisture of line testcrosses to a Corn Belt Dent tester, indicating that the incorporation of a substantial percentage of tropical germplasm in an inbred line does not necessarily negatively impact its combining ability. Thus, tropical maize accessions represent a good source of exotic germplasm to broaden the genetic base of temperate maize without hindering agronomic performance.