Making sense of wheat development: a critique of methodology

Development in wheat is traditionally described in terms of durations of phases between observable events on the apex. The most commonly used events are seedling emergence, the formation of double ridges, and the terminal spikelet on the main stem, and the onset of anthesis. Responses of development to environmental variation is then described in terms of changes in the durations of the phases. We claim that the description itself causes confusion in describing plant responses. This is particularly because the double ridges event is not well coupled to the timing of floral development, and although the formation of the terminal spikelet is an event important for the early development of the ear, it is not a prime determinant of anthesis time. An alternative framework based on the rate of production and numbers of leaves and leaf primordia on the main stem apex, and the coordination of leaf and leaf primordium appearance, provides a simpler and more mechanistic description. We use simulations to show that such a framework explains simply the apparently complex responses of phenophase durations to the environment, and provides a basis for explaining such concepts as 'basic development rate' and 'intrinsic earliness'. (C) 1998 Elsevier Science B.V.