Dynamics of Architectural Development of Isolated Plants of Maize (Zea mays L.), in a Non-limiting Environment: The Branching Potential of Modern Maize

Abstract

The maximal architectural development of a modern maize cultivar (Zea mays L. ‘Dea’) was studied in fully isolated and carefully irrigated plants. Under these favourable conditions, this (usually) non-tillering and non-prolific cultivar displayed a large amount of branching (down to the third order), including large basal tillers and prolific ear shoots. This development was analysed by combining: (1) architectural analysis, initially developed for trees; and (2) quantitative analysis of tillering kinetics, designed for other grass species. The architectural unit of maize included a main long axis (A1) and lateral short shoots bearing a terminal spike (A2). The basal tillers (noted A1′) resulted from a complete and sylleptic reiteration. Its kinetics were consistent with tillering models, but with a particularly long delay in branch emergence (seven phyllochrons), compared to other grass species. This delay is likely to enhance regulation by leaf (or root) density in stands and explains the inhibition of branch development, as usually observed in field conditions, even at low density. Similarly, the suppression of the basal reiteration in secondary branches observed in isolated plants probably results from increased intra-tussock density. In isolated plants, androgenous axes combining A1′ and A2 morphologies were also produced in intermediate positions. It is shown that they can result from a basipetal sequence of A2 differentiation reaching buds in the course of their A1′ development. The consequences of these unexpected results are discussed in terms of maize development and architectural analysis of grasses.