Crop phenotyping for physiological breeding in grain crops: A case study for maize

Abstract

Traditional breeding has been successful in delivering new cultivars with improved grain yield. This is particularly true in the case of maize, with global gains in yield always >2% since the massive introduction of hybrids in the 1960s. The advent of molecular tools in the 1980s, however, demanded an increased knowledge of the whole phenotype for enhancing the breadth of marker-assisted selection. This demand rose during the last decade, and revealed the existence of a large gap between genotypic and phenotypic knowledge, particularly for traits related to the physiological determinants of grain yield (i.e. traits conducive to biomass production and its partitioning). In this chapter, we use maize as a model crop for (1) reviewing general aspects of the physiological model of yield and its dissection in minor traits, (2) examining recent yield gains in major maize-producing countries, and breeding effects on the physiological determinants behind these gains, (3) discussing a field-based approach for phenotyping traits considered critical for yield determination at the crop level, and (4) analyzing possible genetic controls behind the response of yield to its physiological determinants. Opportunities and limitations to the application of field-based phenotyping in maize breeding are also addressed.