Agriculture Reference
In-Depth Information
main shoots have a panicle 1 to 2 mm long, above the airpace
or internode. The early changes associated with the start
of panicle initiation are microscopic in size and impossible
to detect with the naked eye. Panicle initiation depends on
temperature, variety, nitrogen fertility, plant population and
water depth during tillering.
The reproductive phase, i.e., panicle initiation to fl owering
is about 35 days and ripening phase is about 30 days on an
average.
Panicle formation is the change from vegetative apical
meristem to a reproductive apical meristem. Panicle exsertion
is the exsertion of the panicle above the fl ag leaf sheath after
anthesis. It is generally accepted that cold tolerance of rice at
one stage is different from another stage. Panicle formation
is interrupted by the low temperature (Okabe and Toriyama
1972). Days to complete heading varies with the variety, the
range being 5-15 days. By comparison, vegetative shoot apical
meristem is very small, usually completely hidden within leaf
sheath. The panicle exsertion can be classifi ed as well exserted,
moderately well exserted, just exserted, partly exserted and
enclosed.
In aman rice cultivation deviation from the optimum
planting time may cause incomplete and irregular panicle
exsertion, increased spikelet sterility (Magor 1984). Under
temperate condition or in hill altitude similar results are noted
in many varieties.
Rice is very sensitive to cool temperatures during the
reproductive period (Yashida 1981). Although the main
symptom of damage from cold is the high spikelet sterility
(Jacobs and Pearson 1994), incomplete panicle exsertion has
been cited as a symptom as a cold injury in many countries
(Chung 1979, Hamdani 1979, Alvarado and Grau 1991). Cold
