Progress from Selection in Eight Tropical Maize Populations Using International Testing1

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Abstract
Eight full‐season tropical maize (Zea mays L.) populations were improved by the International Maize and Wheat Improvement Center (CIMMYT) using full‐sib (FS) selection and international testing. Cycles CO, C2, and the latest (fourth or fifth) cycle of selection were evaluated at six locations to measure the progress from FS selection. Gains per cycle, averaged over the eight populations for yield, days to silk, plant height, ear height, ear rating, and ears per plant were 1.31, −0.59, −1,06, −1.77, −1.15, and 0.87%, respectively. The ranges in improvement for the same traits were, −0.04 to 1.90, −0.93 to 0.27, −1.89 to 0.75, −3.38 to 0.36, −3.41 to 0.71, and 0 to 1.92%, respectively. In all environments, the latest cycles of selection yielded higher than CO. Our results suggest that FS selection is an effective method for improving maize populations and that the progress per cycle would vary with the selection intensity, quality of data, type of FS selection, and the heritability of the trait. Improved CIMMYT maize populations as such, experimental cultivars developed by recombining among their superior families, as well as their superior FS families are being used by national programs as cultivars, in hybrid combinations, and for extraction of inbred lines.