Developing synthetics as a byproduct of hybrid maize breeding

All-India Coordinated Research Project on maize breeding, established in 1957, started a large-scale multi-parent hybrid breeding and later focused on composite breeding. The improved cultivars did create an impact but not on the expected scale in spite of the development of some outstanding cultivars. Meanwhile, the cultivation of single-cross hybrids became popular in a large number of countries. The breeding programme in India was accordingly reoriented in the late 1980s with an almost exclusive focus on single crosses. These hybrids have created a remarkable impact by accelerating area expansion and yield enhancement in rabi/spring season, but the impact is lower and also variable across regions during kharif. The Project has developed and recommended 35 cultivars of field corn during 5 years (2017-2021) for cultivation during kharif. These include nine composites (including improved locals) meant for the states generally having difficult ecologies and resource-constrained farmers. Evidently, some centers are working on hybrid and composite breeding, and thus are practically conducting two independent breeding programmes. In such situations, an alternative is breeding synthetic varieties rather than undertaking population improvement, as an adjunct of single-cross breeding. Synthetics, being genotypically heterogeneous populations, are expected to have higher stability of performance than genotypically homogenous single-cross hybrids. These also have the advantage that farmers can produce seed at their own level, which is expected to enable synthetics to have a place in some constrained ecologies in the transient phase. However, single-cross breeding should continue to be the ultimate goal as single crosses have the highest performance potential among various cultivar types.