Principles of Plant Genetics and Breeding

green midrib because of the presence of the juice instead
of air spaces in the pithy tissues.
The number of leaves on the plant varies between 7
and 24 depending on the variety. The sorghum inflorescence
is a panicle that may be loose or dense. It is usually
erect but may curve to form a “gooseneck”. The panicle
has a central rachis, with short or long primary, secondary,
and mature tertiary branches, which bear groups
of spikelets. The length and closeness of the panicle
branches determine the shape of the panicle, which
varies from densely packed conical or oval to spreading
and lax. Sorghum is predominantly self-pollinated.
A fully developed panicle may contain 2,000 grains,
each one usually partly covered by glumes. The grain is
rounded and bluntly pointed, 4–8 mm in diameter, and
of varying size, shape, and color according to the variety.
Pigments occur in the pericarp, testa, or both. Cultivars
with a pigmented pericarp have a yellow or red color.
When the pericarp is white and a testa is present, the
seed color may be buff or bluish-white. When a colored
pericarp and a testa are present, the seeds tend to have a
dark brown or reddish-brown color.
Sorghum races
Five major races of sorghum are recognized – durra, kafir,
guinea, bicolor, and caudatum. They differ in panicle
morphology, grain size, and yield potential, among
other characteristics. Durra sorghums developed primarily
in Ethiopia and the Horn of Africa, from where
they spread to Nigeria and the savanna region of West
Africa. Kafir types originated in eastern and southern
Africa. Guinea sorghums are grown mainly in West and
Central Africa, while bicolor types are the least important
to African production, and occur in East Africa.
Caudatum varieties originated in Kenya or Ethiopia.
Grain sorghum groups
Most of the grain sorghums in cultivation are hybrids,
derived from kafir × milo crosses. The major commercial
groups of grain sorghum are kafir, hegari, milo, feterita,
durra, shallu, and kaoliang.
1 Kafir. These have a thick juicy stalk, relatively large,
flat, dark green leaves and awnless cylindrical heads.
The seed color may be white, pink, or red.
2 Hegari. These types have a more nearly oval head,
more abundant leaves than kafir, and sweeter juice
and hence are more desirable for forage.
BREEDING SORGHUM 511
3 Milo. This group has a less juicy stalk, curly light
green leaves, and smaller leaves and stalks. The head
is short, compact, and oval with large yellow or white
seeds. The plant tillers more than kafir and is more
drought tolerant.
4 Feterita. This group has few leaves, relatively dry
stalks, and an oval compact head with very large,
chalk-white seeds.
5 Durra. This group has dry stalks, flat seeds, and very
pubescent glumes. The panicles are erect but may be
compact or loose. The varieties are chiefly grown in
North Africa, India, and the Near East.
6 Shallu. These are characterized by tall, slender, dry
stalks, a loose head, and pearly while seeds. The varieties
are late maturing.
7 Kaoliang. The varieties in this group have dry, stiff,
slender stalks, an open bushy panicle, and small brown
or white seeds. They are grown exclusively in China,
Korea, Japan, and southeastern Siberia.
Floral biology
Reproductive biology
The sorghum inflorescence is a panicle ranging from
7.5 to 50 cm in length and 12.5 to 200 mm in width.
Morphologically, the panicle (or head) ranges from
compact to open. The spikelets are borne in pairs on
branches arranged in whorls. One spikelet is sessile,
bisexual, and fertile, whereas the other is pedicelled and
male-sterile. The sessile spikelet contains two florets,
one perfect and fertile, while the other is infertile. The
fertile floret has a membranous lemma, a palea, two
lodicules, three stamens, and an ovary with two long
styles with plumose stigmas.
Pollination
Blooming of sorghum starts within 3 days after the
panicle emerges from the boot. Blooming starts at or
near the panicle apex and proceeds downward, the process
lasting 4–7 days. Blooming is hastened by shortday
length and higher temperature. Optimal flowering
occurs at temperatures of 21–35°C. Depending on the
environment, the stigma may remain receptive for 5–16
days after anthesis if a flower is unpollinated. Anthesis
usually occurs in the morning. The anthers dehisce as
they are exserted or soon thereafter, usually becoming
pendant. The pollen is most viable within the first 30
minutes; viability is negligible after 4 hours.