Phytomers, phyllochrons, phenology and temperate cereal development

Extensive research has been conducted on temperate cereal development since the inception of the Journal of Agricultural Science, Cambridge in 1905. This review presents an overview of the orderly and predictable development of wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.). It begins with the concept of building canopies by the formation, growth and senescence of phytomers (the unit comprised of the leaf, axillary bud, node and internode). Morphological naming schemes for uniquely identifying each plant part are then extended to uniquely name each phytomer unit. The role of the phyllochron (rate of leaf appearance) in synchronizing cereal development and phytomer formation is discussed, as is the use of phenology to predict the timing of the formation, growth and senescence of individual components. The complete developmental sequence of the winter wheat shoot apex correlated with growth stages is extended to spring barley. This overview discusses the abiotic factors controlling cereal development, with special attention given to key questions regarding the critical role of temperature. The review concludes with some cautious glances forward to the exciting possibilities for better understanding of mechanisms controlling the phyllochron and phenology being gained from advances in functional genomics and molecular biology.