Response of germination rate

The influence of drying T. emetica seeds, to different extents, on the germination time course is illustrated in Fig. 8.2. Short-term drying (i.e. 2.5 h, sufficient to remove 15% of axis water in this instance) actually enhanced the rate of germination. The rate of germination can be conveniently expressed as the MTG, and the responses of the five species to short-term dehydration are summarized in Table 8.3. In all cases, except T. dregeana, there was a reduction in the MTG (i.e.

Fig. 8.1. Germination time course of seeds (n = 25) of Podocarpus henkelii stored at different temperatures at their initial water content (iwc) or after partial drying (pd) as described in Table 8.1. Solid lines and filled symbols = stored at iwc; broken lines and open symbols = stored after pd. Seeds were stored at 6°C (squares), 16°C (diamonds) or 25°C (circles).

10 15 Time (days)

10 15 Time (days)

Fig. 8.1. Germination time course of seeds (n = 25) of Podocarpus henkelii stored at different temperatures at their initial water content (iwc) or after partial drying (pd) as described in Table 8.1. Solid lines and filled symbols = stored at iwc; broken lines and open symbols = stored after pd. Seeds were stored at 6°C (squares), 16°C (diamonds) or 25°C (circles).

Table 8.2. Final germination percentage of seeds (n = 25) stored at their initial water content (iwc), and after partial drying (pd) and storage as indicated in Table 8.1. Those species for which no data are presented for storage at 6°C had chilling-sensitive seeds that did not survive storage at that temperature. No data are available for Podocarpus henkelii seeds stored at their iwc at 25°C because of severe fungal infection.

Final germination (%)

Table 8.2. Final germination percentage of seeds (n = 25) stored at their initial water content (iwc), and after partial drying (pd) and storage as indicated in Table 8.1. Those species for which no data are presented for storage at 6°C had chilling-sensitive seeds that did not survive storage at that temperature. No data are available for Podocarpus henkelii seeds stored at their iwc at 25°C because of severe fungal infection.

Species

Fresh germination (%)

iwc

pd

iwc

pd

iwc

pd

Podocarpus henkelii

100

1 00

60

1 00

68

88

Trichilia emetica

100

1 00

20

1 00

0

T. dregeana

100

12

12

1 00

1 00

1 00

1 00

Ekebergia capensis

100

90

60

75

40

Syzygium cumini

100

60

15

1 00

25

Fig. 8.2. The effect of drying time on the germination time course of seeds (n = 25) of Trichilia emetica. Solid line and filled squares = fresh undried seeds; broken lines = seeds partially dried for 2.5 h (open circles) or 18 h (open triangles). Corresponding water contents are given in Table 8.3.

ra c

Time (days)

Time (days)

Table 8.3. Axis water content (wc; g/g ± one standard deviation) and mean time to germinate (MTG; in days) of fresh seeds, seeds after mild dehydration and seeds after more severe partial dehydration. Drying times (dt; in hours) are indicated. For species where data for partial dehydration are not shown, drying beyond the level described as mild dehydration led to loss of germination capacity.

Fresh Mild dehydration Partial drying

Table 8.3. Axis water content (wc; g/g ± one standard deviation) and mean time to germinate (MTG; in days) of fresh seeds, seeds after mild dehydration and seeds after more severe partial dehydration. Drying times (dt; in hours) are indicated. For species where data for partial dehydration are not shown, drying beyond the level described as mild dehydration led to loss of germination capacity.

Species

wca

MTG

dt

wc

MTG

dt

wc

M TG

Podocarpus henkelii

1.82

11.5

22

1.80 ± 0.13

9.0

163

1.61 ± 0.13

14.6

Trichilia emetica

2.13

5.1

2.5

1.77 ± 0.23

4.3

18

0.80 ± 0.18

5.4

T. dregeana

2.92

8.9

3.5

2.16 ± 0.30

10.8

Ekebergia capensis

1 .28

3.3

6

0.94 ± 0.21

5.9

Syzygium cumini

1.66

6.2

23

1.64 ± 0.36

5.9

aStandard deviations for axes from fresh seeds are as in Table 8.1.

aStandard deviations for axes from fresh seeds are as in Table 8.1.

an increase in the germination rate) after mild dehydration. Further drying led to either an increase in the MTG (P. henkelii and T. emetica) or a loss of germinability, under which conditions the MTG becomes less meaningful.

Was this article helpful?

0 0

Post a comment