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United States Department of Agriculture

Agricultural Research Service

Research Project: OBJECT MODELING AND SCALING OF LANDSCAPE PROCESSES AND CONSERVATION EFFECTS IN AGRICULTURAL SYSTEMS

Location: Agricultural Systems Research Unit

Title: Development of the Wheat Plant

Author
item McMaster, Gregory

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 13, 2008
Publication Date: April 1, 2009
Citation: Mcmaster, G.S. 2009. Development of the Wheat Plant. In: Carver, B.F., editor. Wheat:: Science & Trade. Blackwell Publishing. p. 31-55.

Interpretive Summary: Wheat development is important both in creating plant parts such as leaves and roots needed to capture resources and also in creating the structures ultimately needed to produce viable seed or the desired quality for grain. Development of the wheat canopy can be considered at many scales of the plant but often is first viewed at the highest scale of the whole-plant canopy. The canopy can also be considered as the result of the appearance, growth, and abortion or senescence of shoots or tillers. At the lowest scale, each shoot consists of a basic phytomer unit. A phytomer unit is normally considered to be the leaf, node plus internode above the node, and an axillary bud. The axillary bud gives rise to new shoots, or tillers, in wheat. A shoot therefore can be viewed as the appearance, growth, and abortion or senescence of phytomers, or components of the phytomers, that leads to dynamically changing canopies over the growing season and among years. Regardless of scale considered, morphological naming schemes have been developed to uniquely identify all parts of the plant, and phenology growth staging scales describe the progress of the tiller or canopy through the life cycle. Wheat development is orderly and predictable. Genetics provides the orderliness of development, and environmental factors, mainly temperature, are used to predict development. Thermal time is used as an estimate of the biological clock the wheat plant uses to mark time. Thermal time can be calculated many different ways, but most fundamentally an average temperature (Tavg) is estimated over a time interval (often daily) and used in a temperature-response function to determine the effectiveness of temperature on development rate. The external phenological progression though the life cycle has also been coordinated with developmental events occurring at the shoot apex, resulting in the complete developmental sequence of the tiller or canopy. Simulation models of wheat have increasingly incorporated these developmental concepts to varying degrees. Much of the work describing wheat development is quite empirical, but molecular biology is contributing newfound understanding to underlying genes and mechanisms controlling developmental events. Genetic pathways controlling flowering and plant stature are notable achievements in new understanding.

Technical Abstract: 1) Wheat development is important in creating structures such as leaves and roots needed to capture resources, and also to create the structures ultimately needed to produce viable seed or the desired quality for grain. 2) Wheat canopy development can be considered at many scales of the plant but often is first viewed at the highest scale of the whole-plant canopy. The canopy can also be considered as the result of the appearance, growth, and abortion or senescence of shoots or tillers. At the lowest scale, each shoot consists of a basic phytomer unit. 3) A phytomer unit is normally considered to be the leaf, node plus internode above the node, and an axillary bud. The axillary bud gives rise to new shoots. The root nodal bud should also be considered to be a part of the vegetative phytomer unit. A shoot therefore can be viewed as the appearance, growth, and abortion or senescence of phytomers, or components of the phytomers, that leads to dynamically changing canopies over the growing season and among years. 4) Regardless of scale considered, morphological naming schemes have been developed to uniquely identify all parts of the plant, and phenology growth staging scales describe the progress of the tiller or canopy through the life cycle. 5) Wheat development is orderly and predictable. Genetics provides the orderliness, and environmental factors, mainly temperature, are used to predict development. Thermal time is used as an estimate of the biological clock the wheat plant uses to mark time. Thermal time can be calculated many different ways, but most fundamentally an average temperature (Tavg) is estimated over a time interval (often daily) and used in a temperature-response function to determine the effectiveness of temperature on development rate. 6) The external phenological progression though the life cycle has also been coordinated with developmental events occurring at the shoot apex, resulting in the complete developmental sequence of the tiller or canopy. 7) Simulation models of wheat have increasingly incorporated these developmental concepts to varying degrees. 8) Much of the work describing wheat development is quite empirical, but molecular biology is contributing newfound understanding to underlying genes and mechanisms controlling developmental events. Genetic pathways controlling flowering and plant stature are notable achievements in new understanding.

Last Modified: 8/29/2014