OPTIONS FOR BREEDING FOR GREATER MAIZE YIELDS IN THE TROPICS

Options for breeding for greater maize yields in the tropics were quan titatively examined with a crop growth simulation model that was teste d against field data of five genotypes in four environments. Simulatio ns indicate that at high production levels, grain filling of maize is sink-limited, and that increasing the number of kernels per m(2) throu gh larger primary ears, prolificacy or greater plant densities, will l ead to increased grain yields. On a theoretical basis, it is concluded that larger primary ears lead to greater grain yields at all plant gr owth rates, and that increased prolificacy leads to greater grain yiel ds only if plant growth rate exceeds a threshold. Under nitrogen limit ed growing conditions, selecting for genotypes that extract more nitro gen from soils, and for delayed leaf senescence, show promise for incr easing yields. For crop growth limited by moisture availability around flowering, continued selection for improved kernel set leads to great er grain yields. (C) 1997 Elsevier Science B.V.