Environmental modulation of yield components in cereals: Heritabilities reveal a hierarchy of phenotypic plasticities

Yield components are relatively easy to measure and their interpretation is intuitive. However, strong environmental influences, genetic and physiological controls, and evolutionary constraints collectively lead to lack of independence among yield components that restrict their value in breeding and agronomic applications. Here, we first sketch a framework of plant responses to environmental factors to highlight the modulation of yield components by resources and their interplay with non-resource factors including developmental cues (e.g. maternal effects), extreme events (e.g. frost), predicting factors (e.g. photoperiod) and synchronising and integrating information (e.g. spectral composition of light). We suggest that, to the extent that non-resource cues allow plants to predict future availability of resources, simple resource-based models may be sufficient to capture the macroscopic responses of yield components to the environment. Next, we expand the original concept of hierarchy of plasticities between grain size (a relatively stable trait) and grain number (a plastic trait) to test the hypothesis of a broader hierarchy in the plasticities of yield components. Using published data for wheat, rice, barley and triticale, we verified that heritabilities capture the established hierarchy between plasticity of grain size and number. Median heritabilities of 0.31 for tiller number, 0.58 for inflorescence number, 0.59 for grains per inflorescence, and 0.79 for grain size supported the hierarchy of plasticities: tiller number > inflorescence number approximate to grains per inflorescence > seed size. The heritability of grain yield was consistently higher than the heritability for tittering, consistently lower than the heritability for grain size, and suggestively close to the heritability of inflorescence number and grains per inflorescence, the components of grain number per unit ground area. We conclude that understanding the environmental regulation of yield components in cereals would benefit from a dual focus on yield-related traits per se and their plasticity. (C) 2011 Elsevier B.V. All rights reserved.