Agriculture Reference
In-Depth Information
used rather than “F” for fl oret. Each part of
the infl orescence can be identifi ed by combining
the spikelet and fl oret/caryopsis designations.
For instance, S1F1 refers to the basal fl oret on the
fi rst spikelet of the infl orescence. If the shoot-
naming scheme is added, the specifi c infl ores-
cence on the plant can be identifi ed (e.g., T1S1F1).
As with tillers, missing fl orets or spikelets, or
very small caryopsis, indicates a stressful condi-
tion leading to abortion or reduced growth of
these organs.
axils of leaves on the MS are considered primary
tillers, those from axils of leaves on primary tillers
are secondary tillers, and so on. All tillers are
designated with a “T” and then numbers. For a
primary tiller, the number is a single digit that
refers to the leaf number with which the axillary
bud is associated. For example, T1 is the tiller
emerging from the fi rst leaf (L1) on the MS. Sec-
ondary tillers are given a two-digit designation,
with the fi rst digit referring to the primary tiller
number and the second digit referring to the leaf
number. For example, T21 is the tiller emerging
from the fi rst leaf (L1) on the primary tiller T2.
This system continues for tertiary tillers with a
three-digit designation, and so on. The somewhat
anomalous coleoptile tiller, which emerges from
the axil of the coleoptile leaf, is designated as
either T0 (Klepper et al., 1982, 1983a) or TC
(Kirby and Eisenberg 1966; Kirby and Appleyard
1984).
Knowledge of the presence or absence of spe-
cifi c tillers has been used to provide information
on how the wheat plant perceives its environ-
ment. For instance, the proportion of T0 tillers
present can indicate the seedbed conditions for
seedling emergence. Also, in returning to the
window of time that a tiller can appear, the
absence of a given tiller indicates conditions were
suffi ciently stressful to prevent the development
and growth of the axillary bud.
Roots
The wheat root system consists of seminal and
nodal roots. Seminal roots (usually fi ve to six
roots from one seed) are those originating from
primordia found in the seed, and nodal roots are
those produced from primordia developed after
germination (Klepper et al., 1984). The naming
system created by Klepper et al. (1984) applies to
both seminal and nodal roots. At each node of the
shoot, two roots can appear at opposite sides of
the node (X and Y zones); two other roots can
appear at opposite sides of the node (A and B
zones), but rotated 90 º from the X and Y zones.
Naming schemes for shoots can be applied for
nodal roots, with seminal roots originating from
the MS. In this system, the timing of root appear-
ance is integrated with leaf appearance (Rickman
et al., 1995). The timing, appearance, and growth
of tillers and roots as a function of nitrogen fertil-
izer was examined and found to be strongly
impacted by N fertility (Belford et al., 1987).
Infl orescence parts
The leaf and tiller morphological naming schemes
have been extended to the wheat infl orescence.
Klepper et al. (1983b) devised a numerical index
for the developmental stages of the infl orescence,
which extended phenological growth staging
scales discussed later in this chapter. However,
the morphological naming scheme was not com-
pletely developed. Wilhelm and McMaster (1996)
proposed a spikelet-naming scheme similar to the
leaf-naming scheme: the fi rst spikelet at the base
of the spike is designated S1, with subsequent
spikelets numbered acropetally until the terminal
spikelet. Each fl oret is also numbered acropetally
from the base of the spikelet (e.g., F1, F2,
etc.). If referring to the caryopsis, then “C” is
SHOOT DEVELOPMENT
Morphological naming schemes allow for nonde-
structive identifi cation of plant parts and provide
a context for understanding the developmental
processes leading to the appearance, growth, and
abortion or senescence of the plant parts. The
developmental processes leading to the plant parts
are a result of the developmental sequence of
the shoot apex and the external developmental
stages of the entire shoot (i.e., phenology). Most
developmental events occurring at the shoot
apex cannot be observed without destructive sam-
