Random amplified polymorphic DNA-based evaluation of diversity in the hierarchical, open-ended population enrichment maize breeding system

Commercial maize germplasm has a narrow genetic base. The hierarchical, ope n-ended population enrichment (HOPE) maize (Zea mays L.) breeding system wa s created with the dual purpose of developing useful inbred lines and of di versifying the maize breeding germplasm. The objective of this study was to estimate the genetic diversity in the HOPE populations at initiation and a fter 15 yr of operation. The HOPE system has two heterotic population sets (A and B). Each set has a hierarchical structure and consists of four open- ended populations: elite (E), high (H), intermediate (I), and low (L). New germplasm is added to the system, and high-performing entries from a lower level can be advanced to the next higher level. Increasingly stringent recu rrent selection procedures are employed at each higher level of the hierarc hy. Twelve random amplified polymorphic DNA (RAPD) primers were used to ana lyze 19 plants from the initial and last cycle of selection for each of the four levels of the two population sets. The greatest polymorphism (65.9%) was observed for the last selection cycle of the L level of the B set, whil e the last selection cycle of the E level of the A set was the least polymo rphic (39.2%). Intrapopulation diversity was the greatest for the L level, and the smallest for the E level. Diversity appeared to be enhanced due to introgressions and advancements of material in the hierarchy. Principal com ponent (PC) analysis indicated that the populations of the lower levels wer e more similar to one another than were the two E populations. All polymorp hisms present in commercial check hybrids were also observed in the HOPE po pulations, while 32 of the observed 91 bands were polymorphic in the HOPE s ystem and monomorphic in the hybrids. This study indicates that HOPE popula tions offer variability not present in commercial material and supports the HOPE system as a source of nontraditional germplasm for maize breeding pro grams.