The evolution of hybrid maize breeding in Zimbabwe: Ingredient for the revolution in maize yields - Addis Ababa (Ethiopia) CIMMYT : 1997 - Printed
The development and release of varietal products from the government maize breeding programme of Zimbabwe evolved through stages when emphasis was on open pollinated varieties (from 1904 to 1932), double cross hybrids (from 1932 to l975), single cross hybrids (from 1960 to the present), three way hybrids (from 1969 to the present) and modified single cross hybrids (from 1977 to the present). For the period under study (1913/14 to 1994/95) the graph of annual average yield levels of maize in the commercial farming sector against year rose from just below one tonne per hectare during the open pollinated varieties era to above five tonnes per hectare during the hybrid varieties era. This occurred simultaneously with the increase in hybrid adoption percentage. When the graph of hybrid adoption percentage against year was about to attain 100% no further increases in yield were observed. This remained so even after hybrid adoption percentage was 100%. Two distinct contributions from the maize breeding programme were influential to the rise in annual average maize yield levels in the commercial farming sector. These are: i) the development and release of double cross hybrids and ii) the development and release of the single cross hybrid, SR52. All the hybrids released after SR52 consolidated the yield gains from hybrid SR52. They filled in 'niches' which could not be served by SR52. In the smallholder farming (communal) sector the results are not as striking as in the commercial farming sector but smallholder farmers benefited from hybrid maize technology especially since 1980. Communal farming sector yield levels were around 0.7 tonnes per hectare before 1981 but from 1981 the graph of annual average yield levels averaged at least one tonne per hectare in all the seasons with good rainfall. The increase in yield from around 0.7 tonnes per hectare to about one tonne per hectare occurred simultaneously with the increase in the graph of deliveries of hybrid maize seed to the communal farming sector. Contributions towards yield improvement from other disciplines like agronomy, soil productivity, extension, seed industry, biometry and plant protection are acknowledged as well since those from breeding are difficult to separate from the rest.
633.15 / EAS No. 5