No abstract

The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.

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Crop models need accurate simulation of leaf canopy development. The thermal interval for leaf tip appearance (phyllochron) is critical for predicting the duration of vegetative development. The phyllochron in maize is shorter in temperate than in tropical and subtropical environments. As existing data has been evaluated in a narrow range of environments, the underlying mechanisms that affect phyllochron have not been adequately examined. The objectives of this study were to quantify the response of phyllochron to environmental variables and determine its stability across maize cultivars, to aid modelers in developing tools which accurately predict phenology. Maize was grown in field experiments at Wageningen, The Netherlands, Temple, Texas, USA, and three sites in Mexico, and in controlled environments at Wageningen. The experiment at Temple included grain sorghum and shading treatments to alter irradiance of the crop. Detailed data on leaf production and environmental conditions were collected. These data were combined with published data from field studies. Maize phyllochron acclimated to temperature and increased as mean daily temperature before tassel initiation increased from 12.5 to 25.