Agriculture Reference
In-Depth Information
Chapter 2
Development of the Wheat Plant
Gregory S. McMaster
SUMMARY
scales describe the progress of the tiller or
canopy through the life cycle.
(5) Wheat development is orderly and pre-
dictable. Genetics provides the orderli-
ness, and environmental factors, mainly
temperature, are used to predict develop-
ment. Thermal time is used as an estimate
of the biological clock the wheat plant uses
to mark time. Thermal time can be calcu-
lated many different ways, but most fun-
damentally an average temperature is
estimated over a time interval (often daily)
and used in a temperature-response func-
tion to determine the effectiveness of tem-
perature on development rate.
(6) The external phenological progression
through the life cycle has also been coor-
dinated with developmental events occur-
ring at the shoot apex, resulting in the
complete developmental sequence of the
tiller or canopy.
(7) Simulation models of wheat have increas-
ingly incorporated these developmental
concepts to varying degrees.
(8) Much of the work describing wheat devel-
opment is quite empirical, but molecular
biology is contributing newfound under-
standing to underlying genes and mecha-
nisms controlling developmental events.
Genetic pathways controlling fl owering and
plant stature are notable achievements in
new understanding.
(1)
Wheat development is important in creat-
ing 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 consid-
ered at many scales of the plant but often
is fi rst viewed at the highest scale of the
whole-plant canopy. The canopy can also
be considered as the result of the appear-
ance, 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, the 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 part
of the vegetative phytomer unit. A shoot
therefore can be viewed as the appearance,
growth, and abortion or senescence of phy-
tomers, or components of the phytomers,
that leads to dynamically changing cano-
pies over the growing season and among
years.
(4)
Regardless of the scale considered, mor-
phological naming schemes have been
developed to uniquely identify all parts of
the plant, and phenology growth staging
INTRODUCTION
defi nitions that satisfy all can be diffi cult.
Therefore, for the purpose of this chapter,
growth is defi ned as the permanent increase in
volume, and development is the initiation and
Development and growth are related, but
distinct, processes. As with many terms, precise
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