Inbreeding Depression and Other Genetic Effects in Populations of Maize Containing Highland Tropical Germplasm

A variety cross diallel of five populations of maize (Zea mays L.) was evaluated in a cool, temperate environment. Two of the parental populations were Corn Belt Dent synthetics (AS3 and BS22), one was developed from selected lines from a CIMMYT population developed for highland regions of the tropics and four Corn Belt Dent inbred lines (NZS3), and the other two had the pedigrees ‘Criollo de Toluca’× AS32 (NZS1) and ‘San Geronimo’× BS222 (NZS2). ‘Criollo de Toluca’ is from the highlands of Mexico and ‘San Geronimo’ is from the highlands of Peru. The objective was to study the influence of introgressing highland tropical germplasm into elite Corn Belt Dent synthetics on genetic effects, especially inbreeding depression, and to develop recommendations for the utilization of the introgressed populations. Inbreeding depression explained the greatest proportion of the variation among entries for grain yield, days to silking and plant height, but not for grain moisture at harvest and root lodging. For grain yield, NZS1, NZS2, and NZS3 had high levels of inbreeding depression and the difference between NZS1 and AS3 was statistically significant. High levels of root lodging were associated with NZS1 and high grain moisture at harvest with NZS2. These results indicate that a recurrent selection method, such as S1 selection, which effectively reduces inbreeding depression, should be used in early cycles of selection with introgressed populations containing highland tropical germplasm.