Biomedical Engineering Reference
In-Depth Information
Reproductive Biology
Breeding procedures that are used with a particular crop species are determined by
its mode of reproduction. Understanding the details of phenology, i.e., floral
biology, pollination, fertilization, and seed development in a crop, makes it possible
to develop orderly and efficient breeding procedures.
Panicle Initiation
Sorghum blooming is hastened by short days and long nights. However, varieties
differ in their photoperiod sensitivity [
21
]. Tropical sweet sorghum varieties initiate
the reproductive stage when day lengths return to 12 h. Usually, the floral initial is
15-30 cm above the ground when the plants are about 50-75 cm tall [
22
]. Floral
initiation marks the end of the vegetative growth due to meristematic activity. The
time required for transformation from the vegetative apex to reproductive apex is
largely influenced by genetic characteristics and the environment (photoperiod and
temperature). The grand period of growth in sorghum follows the formation of a
floral bud and consists largely of cell enlargement. Hybrids take less time to reach
panicle initiation and are relatively less influenced by photoperiod and temperature
[
2
,
3
].
Panicle Emergence
During the period of rapid cell elongation, floral initials develop into an inflores-
cence. About 6-10 days before flowering, the boot will form as a bulge in the sheath
of the flag leaf. This will occur, in a variety that flowers in 60-65 days, about
55 days from germination. Sorghum usually flowers in 55 to more than 70 days in
warm climates, but flowering may range from 30 to more than 100 days. These
observations are valid for tropical sweet sorghums, while temperate sorghums that
mature in 5 months take 20-30 days longer for panicle emergence [
2
,
3
].
Panicle Structure
The inflorescence is a raceme, which consists of one or several spikelets. It may be
short, compact, loose, or open and composed of a central axis that bears whorls of
primary branches on every node. The spikelet usually occurs in pairs, one being
sessile and the second borne on a short pedicel, except the terminal sessile spikelet,
which is accompanied by two pediceled spikelets. The first and second glumes of
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