Chapter 16 - Breeding challenge: improving yield potential

Abstract

This chapter reviews recent progress in yield potential of wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) and examines its physiological basis. Rates of genetic gain in yield potential appear to be slowing in wheat, rice and to a lesser extent in maize, although progress has not stopped. Current genetic progress is associated with increases in both biomass and harvest index. Evidence suggests a contribution of increased radiation-use efficiency (above-ground biomass per unit radiation interception, RUE) before and around flowering is linked with recent genetic increases in biomass. Since harvest index is approaching values close to theoretical maxima in some regions and countries, future progress will increasingly depend on continued gains in biomass. In future activities to support high yield potential, priority traits include: (1) enhanced RUE before and around flowering through increased maximum photosynthetic rate at saturating irradiance at the leaf level and optimizing the coupling between the extinction of nitrogen and radiation in the profile at the canopy level; (2) deeper root systems for increased water and nutrient uptake; (3) optimized structural stem DM partitioning to increase ear/panicle DM at flowering; (4) increased fruiting efficiency (grains per unit ear/panicle dry matter at flowering) to enhance grains per unit area; and (5) increased potential grain size by reducing dry matter requirements of cell division and expansion and optimizing plant signaling. Increased understanding of these physiological processes is required to exploit traits either directly in breeding or through the development of molecular markers.