A Reappraisal of Potential Grain Yield Determination From Convergent Physiological and Evolutionary Perspectives.

Currently we think of a more or less sequential determination of grain number, which occurs in a species-specific developmental window, and grain size, which is primarily determined during grain filling. Direct physiological evidence demonstrated genetic and environmental influences on ovary size before pollination, and a close link between ovary size and potential seed size. Evolutionary biology (i) indicates that natural selection has favoured the uniform allocation of maternal resources among offspring, and (ii) highlights the selective pressures associated with genomic conflict between parent and offspring, between female and male parents, and among siblings. The simultaneous definition of seed number and potential seed size is therefore consistent with both physiological evidence and evolutionary theories. By defining number and potential size of seed simultaneously and prior to fertilisation, a strong maternal control of resource allocation is exerted that favours uniform offspring size and constrains genomic conflict.