Seed sterility and germination problems in Schima wallichii (DC.) Korth. and S. khasiana (Dyer) Bloemb

· Articles
Authors

Sanjiban Goswami

St. Edmund’s  College, Shillong – 793003, Meghalaya, India

e-mail: sanjiban2000@yahoo.com

Abstract

Seed sterility and germination problems in S. wallichii (DC.) Korth. and S. khasiana (Dyer) Bloemb. (family Theaceae) has been studied. Production of high percentage of viable seeds with a capacity to germinate quickly is an ideal pre-requisite for the proliferation of tree species. Natural regeneration of S. wallichii (DC.) Korth. and S. khasiana (Dyer) Bloemb (family Theaceae) suffers due to high seed sterility (50%), poor seed germination and high seedling mortality (80 – 90%). Seed germination results showed that 25oC temperature and completed darkness was the favourable condition for germination in S. khasiana seeds. However, temperature did not have significant affect on the germination of S. wallichii seeds. In both species entire process of embryo germination was completed earlier than the seeds. Thus, the seed coat has slowed germination process in both species. Small proportion of filled seeds and lower percentage of viable embryos could be the reasons for poor regeneration of S. khasiana through seeds in nature. Contrary to this, greater proportion of filled seeds in S. wallichii with higher percentage of viable embryos are the causes of better natural regeneration.

Keywords  Schima, Theaceae, seed sterility, embryo viability

Introduction

Schima wallichii (DC.) Korth. and Schima khasiana (Dyer) Bloemb. are timber trees of commerce restricted to eastern Himalayas, N. E. region of India, Bangladesh, Myanmar, Nepal, Bhutan and China. S. wallichii trees occur in plains and on the hills between 1200-1700 m altitudes. S. khasiana trees do not occur in plains and confined between 1200-2000 m altitudes.

S. wallichii is an out breeding species and is also inefficient reproductively (Goswami et al. 2003; Chauhan et al., 1996). Natural regeneration of S. wallichii and S. khasiana suffers due to high seed sterility (50%), poor seed germination and high (80 – 90%) seedling mortality (Boojh, 1981). In S. khasiana, the distance from the parent tree decreases seed predation and increases germination. Germination of seeds in case of S. khasiana has been found to be better in disturbed strands. An alteration in forest microclimate and microsite characteristics, consequent upon the exposure of the forest floor to insolation, favoured both seed production and germination in the shade-intolerant S. khasiana (Barik et al., 1996). High survivorship and high growth rates of S. khasiana seedlings in large gaps is indicative of the regeneration niche preferred by this species (Rao et al., 1997; Goswami et al. 2010).

Keeping the above facts in view, the present work has been done in order to ascertain possible causes of low fruit and seed set, poor seed germination, high seedling mortality and low seedling establishment in nature.

Materials and Methods

Seeds of S. wallichii and S. khasiana were germinated in petriplates on Whatman filter paper moistened with 10 ml of glass double distilled water in BOD incubator at 20 ± 1oC in dark, in pots filled with mixture of garden soil and cow dung manure in 3:1 ratio, in open garden soil and in natural habitat. Hundred seeds constituted one replicate. Embryos were dissected out from the seeds manually to find out whether all the seeds had normal development. Depending on the presence or absence of embryo, the seeds were classified as filled and empty respectively.

Seeds were also germinated in petriplates on Whatman filter paper moistened with 10 ml of glass double distilled water in BOD incubators at    20 ± 1oC and 25 ± 1oC temperatures and in continuous light, dark and 16 h dark 8 h light conditions to find the effect of temperature and light conditions on seed germination in both the species. The intensity of light was 532 lux. Emergence of radical was considered as germination. Data was recorded regularly till the germination was over. Data were collected on days to commence the germination, days taken to complete the germination and total germination percent.

The effect of temperature and light treatments on seed germinability of both the species was tested with two-way ANOVA (Fixed effect model). For determining germination in soil, seeds of both the species were sown in pots filled with mixture of garden soil and cow dung manure in 3:1 ratio. Data on germination were recorded for 65 days. The emergence of plumule above soil was considered as germination. The data were collected on seedlings emergence above soil, days for germination to be occurred and percent germination.

Seed viability was also determined with the help of tetrazolium salt   (Kuo et al., 1996). For this purpose, seeds of both the species collected in 2010 were soaked in glass double distilled water for 24 h at room temperature (20 ± 2oC). The soaked seeds were decoated manually. Data were recorded on the number of filled (embryo present) and unfilled (lacking embryo) seeds. The embryos obtained from seeds were incubated in 1% tetrazolium solution (w/v) at 30 ± 1oC for 3 h and 6 h respectively. The seed viability was determined using three replicates of hundred seeds each. Seed viability is expressed as percentage seeds having germinable embryos. Differentiation between germinable and non-germinable embryos was made on the degree of tetrazolium staining. Germinable embryos stained dark whereas the non-germinable embryos were those that stained light or did not stain.

For studying germination in natural condition, seeds of both the species were sown in garden soil and forest soil and germination was recorded for 90 days.

Observations

In both the species mature fruits are loculicidal capsules those contain winged seeds (Fig. 1A). The seed may be filled or unfilled (Fig. 1B). In case of S. wallichii, 71% seeds were filled while in S. khasiana only 17% seeds were filled (Table 1). TZ test revealed 92% and 32% embryo viability in S. wallichii and S. khasiana respectively  (Table 2). In the former on an average 64% seeds germinated whereas in latter average germination percentage was 12.6% (Table 2) when seeds were germinated in dark on moist Whatman filter paper at 20oC in BOD incubator (Fig 1C).

Embryo germination in laboratory condition at 20oC was 90% in S. wallichii and 16% in S. khasiana (Table 2; Figs. 2A,). Whereas, in soil (pot) it was 47% in S. wallichii and 8% in S. khasiana (Table 2).

When only filled seeds were germinated in pots filled with garden soil and manure mixed in 3:1 ratio, the germination declined to 49% and 11% in S. wallichii and S. khasiana respectively (Table 2). When randomly collected seeds were germinated in pots only 36% and 11% germination took place in S. wallichii and S. khasiana respectively. Thus percentage germination of S. wallichii seeds in pots was more (49%) when only filled seeds were used and it declined to (36%) when randomly collected seeds were germinated. Seedlings of S. wallichii and S. khasiana emerged after 12 days of sowing and the emergence was complete after 28-30 days (Table 3). However, in about 65 days after sowing of the seeds, on average 36% and 11% seedlings survived in S. wallichii and S. khasiana respectively. When randomly collected seeds of both the species were sown in the open plot, germination varied between 33 to 35% in S. wallichii and 6 to 11% in S. khasiana. When seeds were taken randomly and sown in natural condition i.e. in the forest soil, the average germination was found to be 40% and 8% in S. wallichii and S. khasiana respectively. In S. wallichii percentage germination was found better in forest soil than in garden soil.

Effect of different temperature (20 and 25oC) and light conditions  (continuous light, dark and 16 h dark + 8 h light) on the germination of seeds of both the species revealed that compared to S. khasiana, seed germination started earlier in S.wallichii in both the temperature regimes and in all the light conditions (Table 4). However, at 25oC, germination was over earlier in S. khasiana in comparison to S. wallichii in all the light conditions (Table 4). Seed germination commenced first in both the species when seeds were kept in complete dark both at 20 and 25oC. S. khasiana seeds germinated last in continuous light at 20oC. Germination was faster at 25oC and completed early in dark. However no definite response was evident in S. wallichii seeds (Table 4). Compared to 20oC, seed germination was over in less time at 25oC in both the species. In case of S. wallichii percentage germination was better at 25oC when seeds were germinated in 16 h dark and 8 h light condition. While, in case of S. khasiana germination was found better at 20oC in complete dark. There was marked increase in percentage germination at 25oC when seeds were germinated in complete light condition (Table 4). However, in complete dark, there was marked decrease in germination percent at 25oC compared to 20oC.

To observe effect of seed coat on germination filled seeds and embryos of both S. wallichii and S. khasiana were germinated in pot soil. In S. wallichii filled seed germination started on 13th day and completed on 28th day of sowing. The highest germination occurred on 27th day and the mean germination after 30 days was found to be 49%. On the other hand, the embryos started germination on 12th day and it was completed on 26th day of sowing. The highest germination occurred on 20th day after sowing and the mean germination after 30 days was found to be 47% (Table 3). Germination of embryos started and completed earlier than the seeds but percentage germination was found slightly more in case of seeds. In S. khasiana filled seeds started germination on 12th day and completed on 28th day after sowing. The day of highest germination was found to be 27th day and the mean germination after 30 days was 11%. On the other hand embryos started germination on 12th day and germination was completed on 20th day after sowing. The highest germination occurred on 18th day and the mean germination after 30 days was found to be 8% (Table 3). Though completion time of embryo germination was less (20 days) than the seed germination (28 days), percentage of seed germination was better (11%) than embryo germination (8%).

Surviving seedlings in pots developed normally (Fig. 2C) and showed fast growth. Three months old seedlings were found suitable for planting in the field.

Discussion

Occurrence of empty (unfilled) seeds have been reported in many species such as Emblica officinalis (Srimathi et al, 1997), Anogeissus pendula, Terminalia myriocarpa (Gupta, 1997). In both species entire process of embryo germination was completed earlier than the seeds. Thus, the seed coat has slowed germination process in both species. At 25oC, and completed darkness was the favourable condition for germination in S. khasiana seeds. However no such definite response was seen in S. wallichii. In case of S. wallichii germination was better at 25oC in 16 h dark and 8 h light cycle. In complete dark, there was marked decrease in germination. Thus, temperature did not have significant affect on the germination of S. wallichii seeds (both 20oC and 25oC were equally favourable).

Small proportion of filled seeds and lower percentage of viable embryos could be the reasons for poor regeneration of S. khasiana through seeds in nature. Contrary to this, greater proportion of filled seeds in S. wallichii with higher percentage of viable embryos are the causes of better natural regeneration. Tree species like Anogeissus pendula, Terminalia myriocarpa, Cupressus species, some time produce as high as 90% empty seeds (Thapliyal, 1997).

 

Figures

 

 

Table 1:  Embryo germination at 20oC in Schima species.

Species

No. of seeds

Unfilled seeds (%)

(Seeds without embryos)

Filled seeds (%)

(Seeds with embryos)

Mean germination (%)

(Embryos)

S. wallichii

500

29.20 ± 0.46

70.80 ± 0.08

89.83 ± 3.04

S. khasiana

500

83.00 ± 1.73

17.00 ± 1.33

16.00 ± 8.33

± SE

 

Table 2: Viability and germinability of seeds of Schima species.

Species

Embryo viability (%)

(Tz staining test)

Germination (%)

Seed

Embryo

 Lab.

Pot

Lab.

Pot

        S. wallichii

92.03 ± 1.87

64.39 ± 1.73

48.67 ± 2.08 89.83 ± 3.04 46.67 ± 1.67

S. khasiana

32.00 ± 2.73

12.60 ± 0.46 10.67 ± 3.87 16.00 ± 8.33 8.33 ± 3.04

± SE

 

Table 3: Effect of seed coat on germination of seeds in Schima species.

Species

 Seed / Embryo Total number

Day of beginning

Day of peak

Day of completion

 Mean germination after 30 days (%)

S. wallichii

Seeds

150

13th

27th

28th

48.67 ± 2.08

Embryos

150

12th

20th

26th

46.67 ± 1.67

 S. khasiana

Seeds

150

12th

27th

28th

10.67 ± 3.87

 Embryos

150

12th

18th

20th

8.30 ± 3.07

± SE

 

Table 4: Effect of temperature and light conditions on seed germination of Schima species.

Species

  Temperature                                 condition

 

 

Light

Condition

 

20oC

 

25oC

 

Days to start germination

Days to complete germination

Germination

%

Days to start germination

Days to complete germination

Germination

%

 

 

 

 

S.wallichii

 

Light

 

3rd

26th

62.40 ± 1.38

2nd

23rd

50.80 ± 1.03

16h dark

+

8h light

4th

25th

66.80 ± 1.87

2nd

23rd

71.60 ± 1.33

 

Dark

 

2nd

20th

61.20 ± 1.27

2nd

23rd

68.00 ± 0.08

 

 

 

 

S.khasiana

 

Light

 

11th

28th

6.80 ± 0.46

5th

18th

16.40 ± 1.04

16h dark

+

8h light

7th

26th

13.20 ± 1.04

5th

18th

15.60 ± 1.38

 

Dark

 

4th

25th

16.80 ± 0.80

4th

16th

13.60± 0.04

± SE

References

Barik, S. K., Tripathi, R. S., Pandey, H. N. and Rao, P. (1996). Tree regeneration in a subtropical humid forest: effect of cultural disturbances on seed production, dispersal and germination. J. Appl. Eco.33: 1551-1560.

Boojh, R. (1981). Observations on biological adaptation of a forest ecosystem with emphasis on some tree species. Ph. D. Thesis. North-Eastern Hill University, Shillong.

Chauhan, Y. S. and Katiyar, S. R. (1996). Studies on the reproductive biology of Schima.  I. Pollen germination in S. wallichii (DC.) Korth. J. Tree Sci.15(2):  76-81.

Goswami, S. & Pandey, A.K. (2010). Pollen-Pistil Interaction in Two North-Eastern Himalayan Tree Species: Schima wallichii (DC.) Korth. and S. khasiana Dyer (Theaceae):  The International  Journal of Plant Reproductive Biology, 2(2) pp 197-203

Goswami S, SR Katiyar & AK Pandey 2003. Some aspects of reproductive biology of Schima wallichii (DC.) Korth. In AK Pandey & MR Dhakal (eds). Advances in Plant Reproductive BiologyNarendra Publishing House, Delhi. Pp 275-286

Gupta, B.N. (1997). IUFRO symposium on Innovations in Forest Tree Science and Nursery Technology. Raipur, India. Nobember, 22-25, 1997.

Kuo, W.H.J., Yan, A.C. and Leist, N. (1996). Tetrazolium test for the seeds of    Salvia splendens and S. farinaceaSeed  Sci. and Technol.  24: 17-21.

Rao, P., Barik, S.K., Pandey, H.N. and Tripathi, R.S. (1997). Tree seed germination and seedling establishment in tree fall gaps and understorey in subtropical forest of north-east India. Aust. J. Eco.22: 136-145.

Srimathi, P., Karivaratharaju, T.V., Vanangamudi, K. and Natarajan, S. (1997). IUFRO symposium on innovations in forest tree science and nursery technology. Raipur, India. Nobember, 22-25, 1997.

Thapliyal, R.C. (1997). IUFRO symposium on innovations in forest tree science and nursery technology. Raipur, India. Nobember, 22-25, 1997.

 

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