A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
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nous structure called the ligule,<br />
which may be glabrous or ciliate. Its<br />
size, color, and shape vary among<br />
varieties.<br />
The number <strong>of</strong> leaves in the main<br />
culm is always greater than the<br />
number <strong>of</strong> tillers. The number decreases<br />
from the primary to the tertiary<br />
tillers. The prophyllum is at the<br />
base <strong>of</strong> the main tiller.<br />
Floral organs. The <strong>rice</strong> plant terminates<br />
in an inflorescence (blossom,<br />
flower) called a panicle. Each unit <strong>of</strong><br />
the inflorescence is a spikelet.<br />
—The panicle (Fig. 2.4) grows<br />
from the uppermost internode. The<br />
upper extremity <strong>of</strong> the uppermost<br />
internode, where primary branches<br />
<strong>of</strong> the panicle arise, is called the<br />
panicle base or neck. The axis starting<br />
from the panicle base to its end is<br />
the primary panicle axis. It is differentiated<br />
into nodes and internodes.<br />
The nodes are solid; the internodes<br />
are fistular. In the axils <strong>of</strong> branches<br />
on the panicle are swollen portions<br />
called panicle pulvini. Each node<br />
gives rise to primary branches,<br />
which in turn bear secondary<br />
branches. The secondary branches<br />
bear the spikelets.<br />
—Varieties vary greatly in panicle<br />
length, shape, insertion angle <strong>of</strong> primary<br />
branches, and weight and density.<br />
—The spikelets (Fig. 2.5) are<br />
pedicelate. They have a short axis<br />
called the rachilla. The flower is<br />
borne in the axil <strong>of</strong> two types <strong>of</strong><br />
bracts. The first pair <strong>of</strong> bracts are<br />
sterile, and are known as sterile lemmas<br />
(glumes, empty glumes, or<br />
outer glumes). These may be <strong>of</strong> unequal<br />
size, and are generally smaller<br />
than the fertile glumes. The upper<br />
pair <strong>of</strong> bracts is called the fertile<br />
(flowering) glumes and consists <strong>of</strong><br />
lemma and palea. The glumes<br />
(lemma and palea) and the floral organs<br />
constitute the floret.<br />
2.4 The panicle.<br />
2.5 The spikelet<br />
and flower.<br />
The lemma is a five-nervcd bract<br />
partly enveloping the smaller threenerved<br />
bract palea. The middle<br />
nerve or keel may be hairy or<br />
smooth. These bracts extend into<br />
smaller structures called apiculi. The<br />
apiculus at the lemma is known as<br />
the lemmal apiculus while that at the<br />
palea is the paleal apiculus. The<br />
lemma may also bear an awn, which<br />
is the extension <strong>of</strong> its keel. The surface<br />
<strong>of</strong> the bracts may be smooth or<br />
hairy.<br />
—The flower (Fig. 2.5) is bisexual,<br />
complete, hypogynous, and<br />
zygomorphic.<br />
—The perianth (Fig. 2.5) is modified<br />
and greatly reduced into two<br />
succulent structures called lodicules,<br />
which are adnate to the palea. At the<br />
time <strong>of</strong> flowering, the lodicules help<br />
push apart the lemma and palea at<br />
the base to expose the stamens and<br />
the pistil.<br />
—The androecium (male reproductive<br />
organ, Fig. 2.5) has six stamens<br />
in two whorls. Anthers are<br />
<strong>Rice</strong> plant and its environment 7