Physiological studies on breaking seed dormancy of some trees species and their effects on seedling growth




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Minia J. of Agric. Res. & Develop.

Vol.(26) No.2 pp 233- 252 , 2006
PHYSIOLOGICAL STUDIES ON BREAKING SEED DORMANCY OF SOME TREES SPECIES AND THEIR EFFECTS ON SEEDLING GROWTH
R. M. M. Sayed

Dept. of Forestry, Horticulture Res. Inst. Agric. Center, Giza, Egypt .


Received 8 May 2006 Accepted 27 Jun. 2006



ABSTRACT

This experiment was conducted at the Nursery of the Tropical Farm , Kom-Ombo , under directorate of the Botanical Garden , Aswan during the 2004 and 2005 seasons . The main object of this investigation was to study: I] The germination of Balanites aegyptiaca , Kigelia pinnata , Cassia javanica and Strychnos nux-vomica trees; II]-The efficiency of various chemical and mechanical treatments on seed germination of the previous trees and growth of seedling at 3 months-old and III]- Bioassay test by using tree seeds extracts on germination of lettuce seeds.

The used pregermination treatments for Balanites aegyptiaca and Kigelia pinnata seeds were : (i) Soaking in concentrated sulphuric acid for 5 and 10 min. followed by either direct sowing or soaking in tap water for 24 h.. (ii) Soaking in concentrated ethyl alcohol for 15 and 30 min. followed by either direct sowing or soaking in tap water for 24h. and (iii) Control treatment. On the other hand, Cassia javanica and Strychnos nux-vomica seeds were abrade by sand or file and followed by direct sowing or soaking for 24h. in tap water , plus control treatment.

The best results in the two seasons for germination percentages were recorded as a result of using abrasion by sand followed with soaking in tap water for Strychnos nux-vomica seeds (30%) ; sand abrasion and direct sowing for Cassia javanica seeds (26.5%) ; soaking in ethyl for 15 min. and direct sowing for Balanites aegyptiaca seeds (67%) and soaking in ethyl for 30 min. then soaking in tap water for 24h. for Kigelia pinnata seeds (33.3%) . In addition , the best results for daily germination speed were obtained due to :

(i) Treating of Strychnos nux-vomica seeds by file followed by soaking in tap water . (ii) Abrasion of Cassia javanica seeds by file then direct sowing .

(iii) Soaking of Balanites aegyptiaca seeds in concentrated ethyl for 30 min. then soaking in tap water .

(v) Soaking seeds of Kigelia pinnata in ethyl for 30 min. then soaking in tap water . So , the tallest seedlings at 3 months-age for B. aegyptiaca and K. pinnata were obtained due to using sulphuric acid for 10 min. then the direct sowing of seeds. However , the best seedlings of S.nux-vomica and C. javanica were recorded with file treatment then direct sowing. Bioassay test revealed that germination of lettuce seeds was decreased by using extracts of seeds of the four tree species in comparison with those treated by tap water.
INTRODUCTION

Impermeable seeds are common in many species of trees , that seeds fail to germinate , even when conditions are apparently favorable for germination . Since over 100 years , Nobbe (1876) introduced the term “ hard seed " . Balanites aegyptiaca , Kigelia pinnata , Cassia javanica and Strychnos nux-vomica trees are important trees but have impermeable seeds.

These trees are among the most important tree species in Egypt. Balanites aegyptiaca (L.) Delile , Fam- Balanitaceae, the common name Thorn tree , also called Soapberry tree , Desert date , Egyptian balsam , Lalobe and Heglig . The wood of Balanites is heavy , hard and strong and widely used to make domestic utensils , small farm tools and furniture. It is regarded as a good fuel wood and also produces high quality charcoal; Despite it has nutritional , medicinal and other uses ; Balanites is practically unutilized in Egypt , probably because its natural growth is relatively small and scattered , making it difficult to establish a Balanites industry (C. M. P.,2000).

Kigelia pinnata , DC. Sausage- tree , African trees which attain a height of more than 15m. The tree is very ornamental and needing little care ( Bircher , 1960) .

Strychnos nux-vomica , Linn. , Fam. Loganiaceae and attaining a height of 40 ft. The seeds yield the drugs , nux-vomica and strychnine , and the bark is somewhat used as a tonic ( Bailey , 1963).

Cassia javanica , Java , Sumatra , Fam. Caesalpiniaceae . A small , ornamental trees, the bark contains tannin and fruits are used as a purgative in Malaya ( Bircher ,1960).

In Aswan Botanical Garden, many of rarely and valuable trees reached over-maturity and some of these trees were fall down . Among the important ones in the Botanical Garden are the four species of concern in the present study.

Investigations concerning the effect of pregermination treatments on the germination and vegetative growth of the tree seedlings of the four species are very rare , therefore, other woody trees are reviewed in this respect. Youssef et al (1991) on different Acacia species (A. cyclopis , A. melanoxylon and A. sophorae), reported that chipping the seed coat was the most effective treatment to produce the highest germination percentage and the shortest mean days of germinated seeds per day.

Maximous (1998) on stored Pinus pinea seeds , found that mechanical scarification by rubbing seeds against sand paper gave 61.3 germination percentage for seeds which stored for one year and 43.3% for seeds which stored for two years , while the control of stored for one and two years resulted in 36.3% and 26.3% , respectively. Also, Ebeid (2000) studied the effects of some pregermination treatments on some legume trees, and found that mechanical scarification and concentrated sulphuric acid treatments gave the best results on germination percentage and daily germination speed , as well as , the least days for mean germination rate. He also added that manual scarification followed by sulphuric acid treatments resulted in tallest aerial parts, longest roots and heaviest fresh and dry weight of aerial parts.

The present study was carried out to overcome the impermeability of seeds or in other words breaking its dormancy by soaking seeds in sulphuric acid or in ethyl and mechanical scarification and their effects on growth of seedlings . The investigation also included bioassay test by using tree seeds extract on germination of lettuce seeds.
MATERIALS AND METHODS

This investigation was carried out at the Tropical Farm , Kom-Ombo , Aswan , during two successive seasons (at first week of April 2004 and 2005) . The aim of this study was to investigate the response of germination and seedling growth of Balanites aegyptiaca (L.)Delile , Kigelia pinnata DC. , Cassia javanica Java, Sumatra and Strychnos nux-vomica Linn. seeds to different pregermination treatments.

(1) (1)

* The following treatments were adopted on Cassia javanica and Strychons nux-vomica seeds:



1- Mechanical scarification by sand and direct sowing.

2- Mechanical scarification by sand then soaking in tap water for 24h.

3- Mechanical scarification by steel file and direct sowing.

4- Mechanical scarification by steel file then soaking in tap water for 24h.

5- Control (no treatment) .

(1) (1)


* The following treatments were adopted on Balanites aegyptiaca and Kigelia pinnata seeds.

1- Soaking seeds in concentrated sulphuric asid for 5 min . then direct sowing.

2-Soaking seeds in concentrated sulphuric acid for 5 min. then soaking in tap water for 24h.

3-Soaking seeds in concentrated sulphuric acid for 10 min. and direct sowing.

4-Soaking seeds in concentrated sulphuric acid for 10 min. then soaking in tap water for 24h.

5-Soaking seeds in concentrated ethyl alcohol for 15 min. and direct sowing.

6-Soaking seeds in concentrated ethyl alcohol for 15 min. followed by soaking in tap water for 24h.

7-Soaking seeds in concentrated ethyl alcohol for 30 min. then direct sowing.

8-Soaking seeds in concentrated ethyl alcohol for 30 min. followed by soaking in tap water for 24h.


  1. These treatments were selected after preliminary experiment, which showed the effective concentration and time .




9-Control (no treatment).


All previous chemical treatments were followed by washing thoroughly in running water to avoid any toxicity of the used chemicals.

The seeds were freshly collected after ripening , from Aswan Botanical Garden , except for Balanites aegyptiaca which collected from vigorous trees in Aswan city.



Experimental design:

A split plot design with three replicates was applied. The main plot represented the seeds of four tree species, While the pregermination treatments occupied the sub- plots. Each replicate consisted of 10 seeds ( one seed in bag ) .



Analytical data :

Number of germinated seeds , counted every day till germination became constant for each plant and seed germination was calculated using the following equation:

Germination percentage = No. of germinted seeds x 100

Total seeds no.



  • Daily germination speed was calculated according to Djavanshir and Pourbeik (1976).

D.G.S = Number of germinated seeds

Germination period




  • Seedling growth parameters :

At the end of the experiment after 3 months from sowing , the following data were recorded on the obtained seedlings :

  • Stem length (cm)

  • Root length (cm)

  • Fresh and dry weights of the aerial parts and roots ( gm/plant).


Bioassay test :

Seeds of the investigated trees were ground powdered , 5 gm of seed powder was added to 100 ml of distilled water with stirring . After 24h ., solution was filtered and make different concentrations i.e.0,10,20,40 and 60% ( Sankhla and Sankhla , 1968). Twenty seeds of lettuce were placed in 9 cm. Petri dishes on filter paper and watered by 3 ml of every concentration.

The Petri dishes were maintained at room temperature ( 30 + 5 c). After 20h. from treatment , germination percentage was recorded.

Data were subjected to statistical analysis using “F” test according to Snedecor and Cochran ( 1973) and L.S.D. value for comparisons according to Weller and Duncan ( 1969).



RESULTS AND DISCUSSION

I- Balanites aegyptiaca and Kigelia pinnata :

a) Germination percentage (G%):

The effect of pregermination treatments i.e. soaking in sulphuric acid and ethyl alcohol with different times on germination percentage of B. aegypiaca and K. pinnata seeds during the 2004 and 2005 seasons are shown in Table 1 .Data revealed that the most effective treatment for B. aegyptiaca was soaking seeds in ethyl alcohol for 15 min . then the direct sowing . However , this treatment resulted of 63.3 % in the first season and 70 % in the second season while , the lowest value of 16.7% in the first season and 13.3% in the second season was obtained due to the control.

On the other hand , soaking seeds of K. pinnata for 30 min. in ethyl alcohol then soaking in tap water for 24h. resulted in the highest value in the first season (40 %) and (26.7 %) in the second season of germination compared to the control (Table 1 ) .

b) Daily germination speed ( D.G.S.) :

Concerning the effect of chemical treatments ( sulphuric acid and ethyl alcohol ) on daily germination speed of B. aegyptiaca , data in Table 1 show that chemical treatments accelerated the germination in comparison with the control. However, the highest value of daily germination speed ( D. G. S. ) was recorded with using ethyl alcohol at 30 min. then soaking seeds in tap water for 24 h. in the 2004 and 2005 seasons .



Table 1 : Effect of pregermination treatments on seed Germination percentage (G.%) and Daily Seed Germination Speed (D.G.S) of Balanites aegyptiaca and Kigelia pinnata trees .



Trees


First season (2004)

Second season ( 2005)

Balanites

Kigelia

Balanites

Kigelia

Treatments













G.%

D.G.S

G.%

D.G.S

G.%

D.G.S

G.%

D.G.S

Control

16.7

0.07

13.3

0.07

13.3

0.06

10.0

0.08

Sulphuric acid(5m. 0h)

26.7

0.08

16.7

0.08

33.3

0.07

16.7

0.09

Sulphuric acid(5m 24h)

30.0

0.12

23.3

0.10

50.0

0.11

23.3

0.12

Sulphuric acid(10m. 0h)

26.7

0.09

16.7

0.08

30.0

0.08

16.7

0.09

Sulphuric acid(10m. 24h)

26.7

0.14

33.3

0.12

53.3

0.12

23.3

0.13

Ethyl (15m. oh)

63.3

0.12

23.3

0.13

70.0

0.10

20.3

0.14

Ethyl (15m. 24h)

56.7

0.14

33.3

0.16

50.0

0.13

23.3

0.15

Ethyl (30m. oh)

63.3

0.15

30.0

0.17

60.0

0.14

20.3

0.17

Ethyl (30m. 24h)

50.0

0.17

40.0

0.18

46.7

0.17

26.7

0.18

L.S.D : 5%

12.1

0.02

13.5

0.01

20.4

0.01

12.1

0.01
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