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Allelopathic Effect of Siam Weed (Chromolaena odorata) on Seed Germination and Seedling Performance of Selected Crop and Weed Species

O.B. Adetayo 1, O.I. Lawal2, B.S. Alabi1 and O.F. Owolade3

1 Federal College of Agriculture, Institute of Agricultural Research and Training, P.M.B. 5029, Ibadan, Nigeria, alabidel@yahoo.com .
2
Department of Agronomy, University of Ibadan, Ibadan, Nigeria.
3
Institute of Agricultural Research and Training, P.M.B. 5029, Ibadan, Nigeria.

Abstract

Laboratory and greenhouse experiments were conducted at the Institute of Agricultural Research and Training (IAR&T.), Ibadan, Nigeria to investigate the effect of siam weed extract on Seed germination and seedling performance of some crop and weed species. Siam weed plants comprising of leaves and stems were cut, pounded with pestle and mortal. Five kg of the product was soaked in 20 litres of distilled water for a period of four days (96 hours). The composition was sieved and the extract was kept in a refrigerator at 5C for subsequent experiments. Seeds of three crops – corn (maize) (var. ACR89DMR), cowpea (Vigna unguiculata (L.) Walp var. Ife brown) and soybean (var. Tax 923-2E) and two weeds – Siam weed and tridax (Tridax procumbens L.) were used for the experiment. The seeds were tested for germination with or without extract. Weed and crop seedlings were also established in extract treated or distilled water medium and their growth was monitored. Weed seed germination was inhibited by siam weed extract more than crop seed germination. Maize seed germination was not hindered by siam weed extract while on cowpea and soybean, 14 and 8 percent reduction in seed germination, respectively was recorded when compared with the untreated control. Percent reduction in germination in siam weed treated with the extract was 87 %, when compared with the untreated control . Siam weed extract had some inhibitory effect on soybean growth at the later stage of crop growth, while the growth of maize, cowpea, tridax and siam weed itself was stimulated by siam weed extract.

Media summary

Siam weed extract inhibited seed germination of weeds and crops and stimulated the growth of certain crops.

Key Words

Seed germination, inhibited, stimulated.

Introduction

Siam weed (Chromolaena odorata (L) King and Robinson), a perennial weed belongs to the family Asteraceae. It easily takes over plantations of cocoa, plantain, oil palm, rubber and other long season crops. Observations reveal that in areas where siam weed grows, growth of other plants is always hampered (Akobundu 1987). It is not yet clear whether allelopathy is responsible for such a growth behaviour. Many of the allelochemicals are water soluble substances released into the environment through leaching, root exudation, volatilization and decomposition of plant residues and are affected by several environmental factors (Reigosa et al. 1999). According to Macias (1995), the application of naturally occurring allelopathic substances which are ecologically friendly to agricultural practice is a promising method to control weeds. Allelopathy was used by Chung et al. (2001) to control barnyard grass (Echinochloa crus-galli P. Beauv.) in rice (Oryza Sativa L.). Ahn and Chung (2000) and Chuo (1999) used allelopathy as an ecological control tool against several weeds in rice. The objective of this study was therefore to determine the effect of siam weed extract on the germination and seedling performance of some crop and weed species.

Materials and Methods

Laboratory and greenhouse experiments were conducted at I.A.R.&T., Ibadan, Nigeria (724’N, 354’E) in 1999 to determine the effects of siam weed extract on seed germination and seedling growth of some crop and weed species. Seeds of three crops – corn (maize) (var. ACR89DMR), cowpea (Vigna unguiculata (L.) Walp var. Ife brown) and soybean (var. Tax 923-2E) and two weeds – siam weed and tridax (Tridax procumbens L.) were used for experiments.

Preparation of siam weed extract

Siam weed plants comprising of leaves and stems were cut, pounded with pestle and mortal. Five kg of the product was soaked in 20 litres of distilled water for a period of four days (96 hours). Water was used because most allelochemicals are water soluble (Reigosa et al. 1999; Bhowmik and Doll 1982). The composition was sieved and the extract was kept in a refrigerator at 5oC for subsequent experiments.

Laboratory experiment

Seeds of the five plants, either treated with siam weed extract or untreated comprised the treatments. A Petri dish was lined with sterilized filter paper for each treatment. Four replicates of each dish were made. Twenty five seeds of each of the three crop plants were placed in respective Petri dishes (because of larger crop seed size) while 50 seeds of each weed were placed in respective Petri dishes. Treated Petri dishes were each supplied with 25 ml of extract while the untreated control was treated with 25 ml of distilled water. The Petri dishes were placed in a germinator maintained at 25C. Seeds were surface sterilized with 10% solution of commercial hypochlorite bleach for 5 minutes and rinsed thoroughly with distilled water before use. Germinated seeds (defined as emergence of radicle) were counted 4 days after onset of the experiment and this was continued for a period of seven days thereafter.

Greenhouse experiment

The greenhouse experiment was to determine the effect of siam weed extract on the germination and growth of the seeds of the crop and weed species in a soil medium. Seeds of the five plants, either treated with siam weed extract or untreated were used as treatments. Five replications of each treatment were made. Five kg capacity polyethylene bags were filled with air-dried loamy soil. Twenty five weed seeds were planted approximately 1cm deep, while fifty crop seeds were planted 3 cm deep. Extract solution (150 ml) was added to treated pots, while distilled water was used as control. The pots were watered every other day with 500 ml distilled water. Record of germination percentage was taken for each seed type. Seedlings were thinned to 4 plants per pot 3 weeks after planting (WAP). Data on crop plant height and number of leaves were taken at weekly intervals from 3 to 6 WAP. Data on weeds could not be taken at this period because weed growth was slow. At 4 and 6 WAP for seedlings and 8 and 10 WAP for weed seedling, samples were randomly harvested, dried and weighed to determine dry matter content. Separate T-tests were done on the treated and untreated plants, according to the type of plant.

Results and Discussion

Seed Germination

Crop seed germination was generally less affected by siam weed extract than was weed seed germination (Table 1). In the Laboratory, maize seed germination was not hindered by siam weed extract. On cowpea and soybean, 14 and 8 percent reduction in seed germination, respectively was recorded when compared with the untreated control. Although, weed seed germination in the laboratory was generally low, percent reduction in germination in siam weed treated with the extract was 87 %, when compared with the untreated control. Germination of tridax was poor and therefore the effect of the treatment could not be ascertained. The same trend of germination was maintained in the greenhouse except that the weed seed germinated better than in the laboratory. This may suggest that the weed seeds in the laboratory were exhibiting dormancy which may have been broken by seed’s interaction with soil components. Various biological, chemical and physical components may be responsible. Akobundu (1987) listed factors such as soil temperature, soil moisture regime, alternate wetting and drying of soil, soil nitrate level among others as those that affect seed germination. Although, the effect was slight on crop seeds and more on weed seeds, this report is corroborated by the findings of Oke (1988) that siam weed extract inhibited the germination of seeds of cowpea, soybean and tridax.

Table 1. Effect of Siam Weed extract on seed germination of crop and weed species

Treatment

Maize

Cowpea

Soybean

Tridax

Siam weed

% Germination of Seed+

         

Laboratory

         

Siam weed extract

98a

60b

70b

0a

5b

Untreated

98a

70a

76a

3.6a

40a

           

Greenhouse

         

Siam weed extract

95a

60a

68a

48a

8a

Untreated

93a

69a

71a

61a

54a

Means within the same column followed by different letters differ significantly at the 5% probability level.

+ cumulative germination taken from 4 to 11 days after planting.

The inhibitory effect of siam weed extract on germination of its seed is in agreement with the findings of Bhowmik and Doll (1982) and Johnson and Harold (1986) who observed that many weed species exhibit allelopathic (autotoxic) effects on the germination of their own seeds.

Table 2. Effect of Siam Weed extract on height of crop plants.

 

Time( Weeks After Planting)

Treatment

3

4

5

6

 

Maize (height in cm)

Siam weed extract

21.9a

25.6a

31.8a

34.7a

untreated

21.7a

24.3a

26.2b

30.2b

         
     

Cowpea

 

Siam weed extract

13.9a

15.3a

18.8a

21.8a

untreated

14.7a

15.4a

17.1a

18.8b

         
     

Soybean

 

Siam weed extract

12.7a

15.0a

15.6a

21.3a

untreated

12.6a

14.1a

17.4a

22.4a

Means within column followed by different letters differ significantly at 5% probability level.

Table 3. Effect of Siam Weed extract on number of leaves of crops plants.

 

Number of leaves/plant

 

Weeks After Planting

Treatment

3

4

5

6

Maize

       

Siam weed extract

5.0a

6.5a

6.0a

7.0a

untreated

4.0a

5.1a

6.3a

8.0a

         

Cowpea

       

Siam weed extract

12.1a

13.2a

19.2a

28.0a

untreated

11.0a

13.3a

16.0a

23.3b

         

Soybean

       

Siam weed extract

12.2a

13.2a

17.3a

30.3a

untreated

11.1a

12.2a

18.4a

27.6a

Means within column followed by different letters differ significantly at 5% probability level

Growth performance

Weed growth in terms of height and number of leaves could not be assessed because the weeds generally had slow growth and were too tiny to be handled up till 6 weeks of growth assessment. This could not be attributed to the detrimental effect of siam weed extract as the untreated plants were equally affected but to the growth characteristic of the weeds. Alabi (1999) had indicated that the stem girth and number of branches in thorny mimosa (Mimosa invisa Mart) could not be assessed until 6 weeks after establishment due to small plant size. Results of weed dry weight assessed at 8 and 10 WAP (Table 4), show that the growth of tridax and siam weed was stimulated by the extract of siam weed from 8 and 10 WAP and after, respectively. However, this stimulatory effect of siam weed extract would not benefit weeds which germination has been marked prevented (Table 1). The domination of a habitat by siam weed therefore, may be mainly due to weed seed population reduction. Leather (1983) gave a similar report that sunflower (Helianthus annuus L.) residues reduced grass and broadleaf weed population.

Soybean plant height and number of leaves were not affected by siam weed extract (Tables 2 and 3). However, the crop dry weight at 10 WAP was markedly inhibited by the extract (Table 4). Maize height and number of leaves in cowpea were stimulated from 5 WAP by siam weed extract. Cowpea dry weight assessment at 10 WAP also shows that the crop growth was stimulated by siam weed extract. These observations agree with the findings of Rahman and Sabagyo (1975), who obtained a stimulated growth of rice plants on soil containing burnt spear grass (Imperata cylindrica (Anderss.) C. E. Hubbard) leaves.

Table 4. Effect of Siam Weed extract on dry matter accumulation of crop plants and weeds

 

Dry matter (g)

 

Crop Plants

Weeds

Treatment

Maize

Cowpea

Soybean

Tridax

Siam weed

Early assessment+

         

Siam weed extract

1.57a

0.66b

0.16b

1.22a

1.19a

untreated

1.55a

0.72b

0.52a

0.77b

1.19a

           

Late assessment

         

Siam weed extract

3.59a

1.99a

0.83b

5.64a

5.56a

untreated

3.24a

1.25b

1.81a

3.69b

4.94b

Means within the same column followed by different letters differ significantly at the 5% probability level.
+First data for crop plants was taken at 4 WAP and that of weeds at 8 WAP, while the second data for crops was taken at 6WAP and that of weeds 10 WAP.

References

Ahn JK and Chung IM (2000). Allelopathic potential of rice hulls on germination and seedling growth of barnyard grass. Agronomy Journal 99, 1162-1167.

Alabi BS (1999). Effect of Growth Characteristics of Thorny Mimosa on the Performance of Cassava. Ph.D. Thesis, University of Ibadan. 157 pp.

Akobundu IO (1987). Weed Science in the tropics: Principles and practices. John Whiley and Sons; 522 pp.

Bhowmic PC and Doll JD (1982). Corn and Soybean response to allelopathic effects of weed and residues. Agronomy Journal 74, 601-606.

Chou CH (1995). Allelopathy and Sustainable Agriculture. In ‘Allelopathy; organisms, process and Application’ (Eds. Inderjit, Dakshini KMM and Einhellig FA). pp 211-223. ACS symposium series 582. American chemical society, Washinton, DC.

Chung IM, JK Ahn and Yun SJ (2001). Assessment of Allelopathic potential of barnyard grass (Echinochloa crus-galli) on rice (oryza sativa L.) cultivars. Crop Protection 20, 921 – 928.

Johnson WC and Harold DC (1986). Effect of three weed residues on weed and crop growth. Weed Science 34, 403-408.

Leather GR (1983). Sunflowers (Helanthus annus) are allelopathic to weeds. Weeds Science 31, 37-42.

Macias FA (1995). Allelopathy in the search for natural herbicide model. In ‘Allelopathy; organisms, process and Application’ (Eds. Inderjit, Dakshini KMM and Einhellig FA). pp 211-223. ACS symposium series 582. American chemical society, Washinton, DC.

Oke AE (1988). The allelopathic potential of Chromolaena odorata on seed germination and seedling growth of vigina unguiculata var. K59 and Zea mays var DMR-SRW and germination of C. odorata and Tridax procumbens weed seeds. B. Agric. Tech. (Crop production) Project Report; The Federal University of Tech., Akure, Nigeria. 14p.

Rahman M and Subagyo T (1975). The effects of alang-alang (Imperata Cylingrica L.) leaves on some upland crops and dead materials of Liambong (Salvinia molesta D. S.) on lowland rice seedlings. In ‘Proceddings of 3rd Indonesian Weed Science Conference, pp252 – 268.

Reigosa MJ, Sanchez-Moreiras A and Gonzalez L (1999). Ecological approach in allelopathy. Critical Review in Plant Science 18, 577-608.

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