PHYSIOLOGICAL BASES FOR YIELD DIFFERENCES IN SELECTED MAIZE CULTIVARS FROM CENTRAL-AMERICA

For the past 30 years, maize (Zea mays L.) improvement has been the most important activity of a collaborative network of national maize researchers from Central America and the Caribbean. Emphasis has been placed on development of hybrids for areas with high yield potential and open-pollinated cultivars (OPCs) for environments limited by biotic or abiotic stresses. This study was conducted to determine the physiological, phenological and morphological bases for yield differences in a group of representative hybrids and OPCs available in the region. Nine cultivars (five hybrids and four OPCs) were evaluated in 11 diverse environments of the region ranging in mean grain yield from 0.5 to 8.0 Mg ha(-1). Hybrids consistently outyielded OPCs by 1.0 to 1.5 Mg ha(-1) across the range of environments tested. Differences in grain yield between hybrids and OPCs were mostly due to greater biomass production, higher harvest index and a larger daily ear growth rate (2.2 g d(-1) ear(-1) for hybrids versus 1.8 g d(-1) ear(-1) for OPCs). Within hybrids or OPCs, however, differences in yield depended on the duration of grain filling and not on ear growth rate. For example, grain filling in higher-yielding hybrids CB-HS7 and HB-85 required about 7 more days than the lower-yielding hybrids P-8916 and H-5. A similar situation existed within the OPCs. A strong negative relationship was detected between grain-filling length and maturity, indicating that earliness and smaller leaf number were associated with longer grain-filling duration and yield. Grain moisture was strongly related to grain phenological development and was independent of cultivar. These results reveal that an effective mechanism to increase maize yield is to select for extended grain filling. Breeding schemes in use should consider these selection criteria.