J. Popi et al., Random amplified polymorphic DNA-based evaluation of diversity in the hierarchical, open-ended population enrichment maize breeding system, CROP SCI, 40(3), 2000, pp. 619-625
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.