PLANT GENETIC RESOURCES Testcross Performance of Semiexotic Inbred Lines Derived from Latin American Maize Accessions

from Oh43 (Darrah and Zuber, 1986). Smith (1988) reported that a small number of lines, including B73, Tropical maize (Zea mays L.) represents the most diverse readily A632, Mo17, and Oh43, were the major contributors to available source of germplasm to broaden the limited genetic base of commercial U.S. maize hybrids. Subsequently, Smith et temperate maize in the USA. One objective of this study was to al. (1999) found that pedigree diversity of Pioneer brand determine if exotic-derived alleles contributing to enhanced testcross agronomic performance were maintained in semiexotic lines created inbreds and hybrids were lower in the 1990s than any by inbreeding and pedigree selection. A second objective was to previous decade. determine if first-generation semiexotic lines could produce hybrids Tropical maize germplasm likely contains unique with agronomic performance comparable to commercial U.S. hybrids. alleles that would be useful to temperate breeding proOne hundred sixty-four semiexotic inbred lines were developed from grams (Crossa and Gardner, 1987; Holland and Goodcrosses between temperate-adapted inbred line Mo44 and 23 Latin man, 1995). Successful incorporation of exotic germAmerican maize accessions. Mo44 and each semiexotic line were plasm has resulted in the creation of new breeding stocks testcrossed to temperate hybrid LH132 LH51 for evaluations. In exhibiting increased yields in maize (Goodman et al., first-stage replicated yield trials, testcrosses of 18 semiexotic lines, 2000) as well as in soybean [Glycine max (L.) Merr., representing six different races, had significantly greater grain yields Thompson and Nelson, 1998], and wheat (Triticum aestithan the Mo44 testcross. Advanced yield evaluations were performed on check entries and 33 selected semiexotic line testcrosses in three vum L., del-Blanco et al., 2001). However, working with additional environments. Across 10 environments, 12 semiexotic line tropical maize in temperate environments is hindered testcrosses exhibited significantly greater grain yield than the Mo44 by photoperiod sensitivity (Brown, 1975) and linkage testcross, indicating recovery of favorable exotic alleles. Semiexotic testbetween favorable alleles and alleles contributing to crosses were not competitive with commercial hybrids for grain yield maladaptation (Brown, 1953, 1988). Furthermore, choosbut were similar to or better than commercial hybrids for grain moising appropriate germplasm sources from among the ture and lodging resistance. Many superior accessions represent relamany thousands of available accessions has been hintively recent introductions into regions from which they were coldered, until recently, by inadequate testing and relected. Tropical landraces seem to be a good source of exotic porting systems (Stuber, 1978; Goodman, 1983, 1999). germplasm that can be used to broaden the genetic base of modern A maize germplasm incorporation program, indepenU.S. maize production and improve productivity. dent of the Germplasm Enhancement of Maize project (Pollak and Salhuana, 1998) and the Latin American Maize Project (Salhuana et al., 1991), has been conI the USA, only limited use is made of the vast ducted at North Carolina State University for about 20 supply of available maize germplasm. Only six of the yr. This program began by screening 1300 typical Latin approximately 300 races of maize in the New World are American maize accessions for agronomic utility (ear represented in commercial cultivars, and only one of and plant height, lodging resistance, and pollination sucthese is used in the USA (Goodman, 1985, 1990). As cess rate) in a nearly daylength-neutral nursery in southof 1996, exotic germplasm contributed less than 3% to ern Florida for 2 yr (Goodman, 1983). Castillo-Gonzalez the pedigrees of U.S. maize cultivars (Goodman, 1999). and Goodman (1989) advanced the best accessions to Interbreeding elite lines derived from a small number replicated yield trials under short-day and long-day phoof open-pollinated cultivars of the Corn Belt Dent race toperiod conditions and identified a subset of accessions for 60 yr has further reduced the genetic diversity of that appeared to have sufficient agronomic value to be commercial U.S. cultivars (Troyer, 1999). For example, useful for breeding. The 40 most promising accessions a 1984 American Seed Trade Association survey rewere selected for conversion to photoperiod insensitivvealed that 16% of new inbred line development came ity by crossing them to temperate-adapted line Mo44 from continually breeding new lines from B73 and 9% and then intermating within each segregating population. Following selection for photoperiod insensitivity, J.A. Tarter and M.M. Goodman, Dep. of Crop Science, Box 7620, four full-sib families were sampled from each of the North Carolina State Univ., Raleigh, NC 27695-7620; J.B. Holland, 40 populations for agronomic evaluation. Holland and USDA-ARS, Plant Science Research Unit, Dep. of Crop Science, Goodman (1995) reported that 24 of these families Box 7620, North Carolina State Univ., Raleigh, NC 27695-7620. Reranked higher than Mo44 for grain yield in testcrosses ceived 18 Nov. 2002. *Corresponding author ([email protected]. edu). to Corn Belt Dent hybrids and concluded that multiple testers were not needed to efficiently identify superior Published in Crop Sci. 43:2272–2278 (2003). semiexotic populations. Holland and Goodman (1995)  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA suggested that inbred lines with good combining ability