Agriculture Reference
In-Depth Information
The type of cold damage that usually occur in the hilly
areas are (1) poor germination and extended germination
period; (2) slow seedling growth, low vigor, leaf discolouration
and mortality; (3) inhibited root-development, growth, and
tillering and nonsynchronous tiller production; (4) delayed
heading and poor panicle exsertion; and (5) spikelet sterility,
low and irregular grain fi lling and early senescence (Kaw 1985).
However, comparatively low temperatures were favourable
for raising short but strong seedlings.
The rooting of rice seedlings occurs favourably over a
range from 9°C and 33°C with an optimum at 25°C-28°C, it
is severly inhibited by temperature below 16°C and above
35°C (Chamura and Honma 1973). Root number also notably
decreased at 9°C-13°C. Cell division and elongation of root cells
in rice seedlings, in root tip cortical cells, cell division was most
active at 25°C, it decreased notably at 15°C, the elongation of
the length of seminal roots at 15°C was very slow (Yamakawa
and Kishikawa 1957). Shimizu (1958) showed that mitosis was
normal at and above 20°C, but very slow at 15°C and ceased
extirely at 10°C (Table 6).
Table 6 Infl uence of low temperature on number of dividing cells and cell length
in rice roots at seedling stage.
Temperature (ºC)
Dividing Cells (no/root tip)
Cell length ( O )
45
40
35
30
25
20
15
0
0
125
175
200
175
140
62
70
97
105
95
80
72
At later stages (3-5 weeks after sowing) temperature affects
the tillering only slightly, except at the lowest temperature 12ºC.
Basically, higher temperatures increase the rate of emergence,
and provide more tiller buds. Under low light conditions,
some of the tiller buds may not develop into tillers because
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