Response to selection over 15 years in the hope maize breeding system

The hierarchical, open-ended, population enrichment (HOPE) maize (Zea mays is L.) breeding system consists of two sets of populations (A and B) vith c omplementary heterotic patterns. Within each set, four open-ended populatio ns are arranged in a hierarchical fashion, based on agronomic performance: low (L), intermediate (I), high (H), and elite (E). At these four levels, d ifferent and increasingly more stringent recurrent selection procedures are applied. The goal of the system is to diversify the germplasm base current ly used in maize breeding programs, while at the same time providing germpl asm for developing commercially useful inbred lines. The objective of this study was to evaluate the first 15 years of HOPE selection. With the except ion of EA, the performance index (PI = grain yield x 1000 moisture) vas imp roved in all populations. Performance index of the population crosses was s ignificantly improved at all levels. Lodging vas significantly reduced in a ll Populations and population crosses, with the exception of the cross of L A and LB. More heterosis was present at the E level than at (lie lower leve ls. The HOPE system was successful in improving performance of the populati ons, the rate of improvement being comparable with that reported for closed populations. The employment of two heterotic sets and four hierarchical le vels, however, was not reflected in the performance of the populations and crosses. Consequently, the HOPE system has been condensed to three hierarch ical levels (L ', H ', and E ') with only one population at each of the L ' and H ' levels, but reciprocal populations are continued at the E ' level.