Agriculture Reference
In-Depth Information
Temperature (°C)
Crop species
Minimum
Maximum
Optimum
Rice (
Oryza sativa
)
10
45
20-35
Wheat (
Triticum aestivum
)
20
40
25-30
Maize (
Zea mays
)
10
40
25-30
Soybean (
Glycine max
)
10
35
25-30
Tomato (
Solanum lycopersicum
)
11
30
15-27
Cucumber (
Cucumis sativus
)
18
30
25-30
Egg plant (
Solanum melongena
)
15
33
20-25
Peeper (
Capsicum
spp.)
15
35
20-30
Pumpkin (
Cucurbita moschata
)
15
40
20-25
Water melon (
Cucumis melo
)
15
35
25-30
Lettuce (
Lactuca sativa
)
4
25
15-20
Carrot (
Daucus carota
)
11
30
15-25
Cabbage (
Brassica oleracea
var.
capitata
)
8
35
15-30
Spinach (
Spinacia oleracea
)
5
30
15-20
Table 1.
Ranges of temperatures for seed germination of different crops [21, 22]
Roberts [23] documented three distinct physiological processes during seed germination
which are affected by temperature: 'first, temperature, together with moisture content,
determines the rate of deterioration in all seeds; second, temperature affects the rate of
dormancy loss in dry seeds and the pattern of dormancy change in moist seeds; and, third, in
non-dormant seeds, temperature determines the rate of germination' (for review see [24]).
The effect of HT on germination was investigated in various crops and serious impacts of HT
on seed germination were observed. Increasing temperature between base and optimum
temperatures increased the rate of germination and total percentage germination, but tem‐
peratures above optimum decrease the germination percentage [Prasad et al. 2006]. Essemine
et al. [25] observed that very HT (45°C) did not allow adequate rate of germination due to cell
death and embryo damage in
T. aestivum
during the early stage of development (first 6-d of
growth), indicating that HT is not favorable to wheat growth and did not permit establishment
of new seedlings. In some cases, plants grown under HT also produce low quality seeds which
have poor germination and vigor. Recently, Kumar et al. [26] observed that growth of roots
and shoots in hydroponically grown
Phaseolus aureus
seedlings was not inhibited at 35/25°C
(day/night temperature), but at 40/30 and 45/35°C, 18 and 34% reduction of shoot growth was
observed. The root growth at these temperatures was inhibited by 13 and 23%, respectively.
When
Vigna mungo
seeds were exposed to 10, 20 and 30 min of heat (50°C), Piramila et al. [27]
observed that seed germination as well as vigor index was significantly reduced by high
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