Five Years of HOPE: The Hierarchical Open-Ended Corn Breeding System

The hierarchical, open-ended corn (Zea mays L.) breeding system (HOPE) is designed to enhance genetic diversity and breeding potential by continually introgressing a wide range of germplasm into breeding populations concurrently subjected to increasingly stringent recurrent selection procedures. This research evaluated the response to selection after 5 yr. The HOPE breeding system involves two heterotic (A and B) sets of four open-ended populations based on a hierarchy of performance: elite (E), high (H), intermediate (I), and low (L). The 5 yr of selection included two cycles of reciprocal recurrent selection (RRS) at the E level, five cycles of modified ear-to-row (ME) selection at the H and I levels, and five cycles of stratified mass selection at the L level. Selection was for performance index (PI) grain yield ÷ grain moisture. About 90% of the 408 introductions added to HOPE during this period were to the L level. In EA, RRS reduced grain moisture 2.7% per year relative to CO; this was offset by a decrease in grain yield of 3.2% per year. In EB, PI and grain yield increased by 2.0 and 2.7% per year, respectively. In the cross EA × EB, only grain moisture was improved. At the H level of performance, ME selection produced increases of 2.8 and 4.6% per year for PI, 1.4 and 6.9% per year for grain yield, and −0.9 and 1.8% per year for grain moisture, relative to CO, in HA and HB, respectively. At the I level, ME selection improved PI by 3.2% per year and reduced grain moisture by 2.2% per year in IA relative to CO. In IB, only grain moisture was improved. At the L level, mass selection increased PI by 4.0 and 2.1% per year and reduced grain moisture by 2.2 and 1.0% per year relative to CO in LA and LB, respectively. Five years of HOPE resulted in genetic gains, suggesting that selection in open-ended populations, arranged in a hierarchical structure, is a viable breeding strategy. Par ot a thesis by the senior author in partial fulfillment of the requirements for the Ph.D. degree.