Use of the Suwan1 Heterotic Group in Maize Breeding Programs in Southwestern China

Broadening the maize (Zea mays L.) genetic base is essential for improving grain yield. Suwan1, developed from a broad base of tropical germplasm in Thailand, has recently been identified as a heterotic group different from Reid and non-Reid heterotic groups. The objectives of this study were (i) to evaluate the grain yield (GY) of crosses to see if there is value to utilizing Suwan1 as a heterotic group in maize breeding, and (ii) to investigate the general combining ability and specific combining ability to determine if Suwan1 shows good combining ability with Reid and non-Reid heterotic groups for GY. Three testers, one from each of the three heterotic groups, were crossed with 20 elite lines collected from across China. Eighteen lines improved via introgression of exotic germplasm and two lines improved via pedigree selection were crossed with TRL02 (non-Reid), YML46 (Suwan1), and TRL211 (Reid). Grain yield, ear length, ear diameter, kernel rows per ear, kernels per row, and 100-kernel weight of crosses and a check were evaluated at three locations. The results suggested that the Suwan1 X temperate crossing system was a very useful heterotic pattern. Suwan1 improved all five yield components in crosses and demonstrated good combining ability for GY with Reid and non-Reid heterotic groups. We have also determined that the appropriate percentage of introgressed germplasm should be between 6.25 and 12.5%.