Previous PageTable Of ContentsNext Page

Study of allelopathic interference of rapeseed (Brassica napus var.belinda) on germination and growth of cotton (Gossypium hirsutum) and it’s dominant weeds

Masoomeh Younesabadi

Department of Plant Pests and Diseases - Agricultural Research Center of Golestan province-Gorgan-Iran
E-mail myounesabadi@yahoo.com

Abstract

The allelopathic potential of rapeseed was evaluated on germination and growth of cotton and its dominant weeds (Amaranthus retroflexus L., Abutilon theophrasti Medic.) and the possibility of herbicide usage reduction. For these purposes greenhouse experiments were performed as factorial in randomized complete block design with 4 replicates .The first factor had two levels (soil incorporated with rapeseed seedlings in 3-4 leaved stage and control soil) and the second factor had three levels (0,1.5 and 3 L/ha Cobex herbicide[N-N-Diethyl 2, 4 – dinitro - 6 – trifluoroethyl – m – phenylene – diamine]). Also, six weeks after incorporation of rapeseed with soil water extracts were prepared from soil on a weekly basis. The effect of these extracts on growth and germination of above plant were investigated in Petri dishes.

The results showed that A.retroflexus and A.theopherasti germination was reduced through rapeseed treatment but cotton germination had no change. Thirty or 60 days after planting (DAP) was observed significant reduction in growth of A. retroflexus and A. theophrasti and dry weight of cotton. However 60 DAP there were no changes in growth of cotton even fresh and dry weight of cotton through rapeseed treatment was more than control soil. Study in petri dish proved that the third, the forth and fifth week extracts had the most significant effects on the growth reduction. This is probably due to releasing of some growth inhibitor substance from decomposed rapeseed.

Media summary

This research showed that rapeseed has inhibitory effect on early growth and germination through allelopathy.

Key Words

Allelopathy; Brassica napus; Cobex

Introduction

Reduced growth of crops and weeds is often reported following addition of Brassica residues to soil or following Brassica spp. (Golami et al, 1996; Khatib et al, 1997). In rotation recently in Iran cotton plant after rapeseed is common and also sometimes growers have to incorporate rapeseed with soil before harvesting in 4 or 5 leaved stage due to its bad germination. Often, they have to plant cotton or soybean instead of rapeseed, thus survey of the effect of rapeseed on cotton and other crops in Iran is necessary. Therefore, two types of studies were conducted to examine the inhibitory of Brassica napus on cotton and its dominant weeds growth І-green house study and ІІ-petri dish culture (laboratory) study. In study I the effect of Brassica napus were investigated on growth of cotton and its dominant weeds by incorporation of rapeseed seedlings in to the soil .In study II the effect of water extract of soil that Brassica napus was mixed in to was investigated on growth of cotton and its dominant weeds in Petri dish.

Methods

This study was conducted at the Agricultural Research Center of Golestan province in Iran during1997-1998. Rapeseed var Belinda (0.7g) was planted on 21, Nov.1997 in 20 cm-diam cotainers filled with 3kg soil, a mixture of sand silt loam, 0.5kg Ammonium phosphate and 100 g animal manure that had decomposed completely. Rapeseed was grown in the green house at 15-25 C. After 4 months rapeseed was harvested at the 4-5 leaf stage. Total plant tissue was incorporated with soil uniformly. The pots were allowed to decompose for six weeks. The experiment was undertaken using a factorial design with 4 replicates. The first factor had 2 levels (soil incorporated with rapeseed seedlings and soil without rapeseed seedlings) and second factor had three levels (0, 1.5 and 3L/ha Cobex herbicide as pre plant).After performing treatment, 50 seeds of cotton, 100 seeds of velvetleaf and 50 seeds of redroot pigweed were planted in pot separately. Thirty days after planting (DAP) germination percentage was measured, and the seedlings thinned to 10 plants/pot. Then some of the characters such as height, fresh and dry weight of plants that were removed from soil were measured. Sixty DAP the total plants in each pot were removed and measured.

Simultaneously, water from the soil in this experiment was extracted weekly. These extracts were preserved in 4 ˚C for other test. The seeds were planted in several layers of paper and were grown in incubator in 20˚Cand the seeds watered with water extracts. Then seed germination percentages were measured during one week and after 9 days, some of the seedlings characters such as the length of rootlet and hypocotyl, fresh and dry weight of rootlet and hypocotyl were measured. Finally, data were analysed with MSTATC package and LSD was used to determine significant differences among mean values at 0.05 probability level.

Results

Green house study

(a) Effect on crop and weeds germination

The results showed that rapeseed decreased germination of redroot pigweed and velvetleaf. Application of 1.5 L/ha Cobex alone had no significant effect on germination of redroot pigweed but 1.5 L/ha Cobex with rapeseed had a significant effect on its germination. Three L/ha Cobex not only alone but also with rapeseed had a significant effect on germination of redroot pigweed (Table 1). In addition, application of 1.5and 3L/ha Cobex alone was not effective on germination of velvetleaf but 3 L/ha Cobex with rapeseed had a significant effect on germination of velvetleaf (Table 2). Germination of cotton was not affected by treatments (Table 3).

(b) Effect on crop and weed growth

The results of the first bioassay period (30 DAP) indicated that rapeseed alone or with herbicide decreased the total fresh and dry weight of redroot pigweed significantly. The result of second bioassay period (60 DAP) showed that rapeseed with 3 L/ha Cobex caused a significant reduction on growth of pigweed. Also rapeseed not only with herbicide but also without herbicide caused a significant reduction on total dry weight of pigweed. All Brassica species contain glucosinolates, which are hydrolysed to isothiocyanates and there are numerous examples of isothiocyanates inhibiting plant growth or seed germination (Boydston and Hang, 1995; Yamane et al. 1992).

Table 1. Effect of treatments on growth of pigweed

   

30 Days after planting

60 Days after planting

L/ha Cobex

Rapeseed

Germination

Fresh weight

Dry weight

Fresh weight

Dry weight

Length of stem

Length of root

Node number

Leaf number

0

None

43a

755a

66a

7.08a

0.85a

42

11.7a

16a

9a

1.5

None

39ab

728ab

62b

6.71ab

0.82b

41.8

11.3ab

16a

8ab

3

None

26c

680bc

60c

6.57b

0.73d

38.5ab

10.4c

15a

7c

0

Added

41ab

690bc

59d

6.82ab

0.82d

40.3

10.9bc

16a

8ab

1.5

Added

37b

680bc

60c

6.50b

0.79b

38.5ab

11.3ab

15a

8b

3

Added

21d

640c

56e

6.02c

0.67c

35.3b

9.5d

10b

6d

Means within a column followed by the same letter are not different at p=0.05 according to LSD test

Results from 30 DAP showed a significant reduction in total fresh and dry weight of velvetleaf so that rapeseed with herbicide caused more reduction than rapeseed alone. However, the height of velvetleaf was not affected by treatments (Table 2).The result of 60DAP showed that among treatment, rapeseed with 1.5 and 3 L/ha Cobex had a significant effect on growth of velvetleaf. Total dry weight of velvetleaf was not affected by treatments except rapeseed with 3 L/ha Cobex herbicide. Boydston and Hang, (1995) also showed that benzyl-itc is a breakdown product of white mustard and is phytotoxic to velvetleaf.

Table 2. Effect of treatments on growth of velvetleaf

     

30 Days after planting

60 Days after planting

L/ha Cobex

Rapeseed

Germination

Fresh weight

Dry weight

Fresh weight

Dry weight

Length of stem

Length of root

Node number

Leaf number

0

None

50a

124.7a

79.3a

4.71a

0.63a

40.66a

13.75a

12.10a

6.53a

1.5

None

48ab

124.4a

78b

4.63ab

0.62a

40.42a

11.49b

11.82ab

6.18ab

3

أNone

47ab

123.6a

77.3b

4.43ab

0.61a

40.40a

11.76b

11.65ab

6.09ab

0

Added

46abc

120.4b

76c

4.40abc

0.60a

36.64ab

11.05bc

12.03ab

5.73b

1.5

Added

45bc

120.4b

75d

4.12bc

0.60a

36.19ab

11.31b

11.60b

6.15ab

3

Added

42c

119.9b

74.8d

3.79c

0.51b

33.32b

9.62c

11.66ab

6.09ab

The results of the first bioassay period (30 DAP) showed that fresh weight of cotton was not affected by treatments but dry weight and height of cotton decreased significantly so that cotton following by of rapeseed with 1.5 L/ha herbicide had the less dry weight and height. The results of second bioassay period (60 DAP) showed that root and shoot length, node and leaf number of cotton was not affected by treatments. But the total fresh and dry weight of cotton not only was not decreased but also increased significantly with rapeseed although cotton following by rapeseed without herbicide had the highest total height and dry weight. Nitrogen may be mineralized from the decaying rapeseed residues and be utilized by the cotton crop during the growing season. (Boydston and Hang, 1995)

Table 3. Effect of treatments on growth of cotton

   

30 Days after planting

60 Days after planting

L/ha Cobex

Rapeseed

Germination

Fresh weight

Dry weight

Fresh weight

Dry weight

Length of stem

Length of root

Node number

Leaf number

0

None

40.12a

940a

72a

3.64b

0.58b

28.4a

13.9a

6.4a

5.5a

1.5

None

46.29a

1010a

66b

3.77b

0.55b

27.83a

12a

6.6a

5.5a

3

None

42.26a

1060a

67b

4.88ab

0.69b

34.9a

12.1a

7.7a

6.5a

0

Added

36.72a

910a

65b

5.97a

0.96a

34.5a

14.4a

7.6a

6.7a

1.5

Added

39.71a

940a

63c

4.73ab

0.68ab

31a

13.8a

7.2a

5.5a

3

Added

41.60a

950a

66b

4.69ab

0.71ab

34a

13a

7.5a

5.7a

Petri dish study

Effect on crop and weed growth and germination

Studies in Petri dishes showed that the extracts that were prepared from soil during successive weeks had no effect on the length of root and hypocotyl of redroot pigweed, but the fifth week extract only caused a significant reduction on length of rootlet of redroot pigweed. The total extract had a significant reduction on dry and fresh weight of hypocotyl and rootlet and germination of redroot pigweed (Table 4).

Table 4. Effect of water extracts on growth and germination of pigweed

Extract

Germination

Length of hypocotyl

Length of rootlet

Fresh weight of hypocotyl

Dry weight of hypocotyl

Fresh weight of rootlet

Dry weight of rootlet

Non treatment

65a

38a

17a

3433a

180a

933a

950a

First week

60ab

34a

16a

3067b

160b

667c

710d

Second week

58b

35a

16a

3067b

170b

767b

647f

Third week

54b

35a

14ab

3000bc

137d

667c

777c

Forth week

56b

33a

13ab

2900c

150c

667c

680e

Fifth week

54b

32a

12b

2667d

150c

750b

637f

Sixth week

55b

37a

14ab

2733d

163b

733b

830b

Also the results showed that among the extracts that were prepared from soil during successive weeks, only the forth week extract had a significant effect on germination of velvetleaf, also the fourth week extract had the most reduction on length of hypocotyl, dry and fresh weight of hypocotyl (Table 5). The fourth and sixth week extracts had the highest reduction on length of rootlet, dry and fresh weight of rootlet. Leather (1983) also showed that leachate from dried rapeseed tissue inhibited the growth of velvetleaf.

Table 5.Effect of water extracts on growth and germination of velvetleaf

Extract

Germination

Length of hypocotyl

Length of rootlet

Fresh weight of hypocotyl

Dry weight of hypocotyl

Fresh weight of rootlet

Dry weight of rootlet

Non treatment

33a

92a

65a

75.1a

4.4a

15.3a

1.2a

First week

27ab

73bc

61ab

65.7c

3.2cd

13c

1bc

Second week

27ab

74bc

59ab

62.9d

3.4bc

15.5a

1b

Third week

27ab

82ab

63ab

66.1c

3.1d

14.2b

1bc

Forth week

22b

66c

42c

55.2e

3d

10d

0.8d

Fifth week

26ab

83ab

63ab

70.2b

3.5b

13.5c

1c

Sixth week

26ab

78abc

52bc

66.4c

3.3c

9e

0.8d

Study in Petri dishes proved that the extracts that mentioned above had not an effect on the germination and length of rootlet of cotton (Table 6). But, the third week extract only caused a significant reduction on length and fresh weight of hypocotyl of cotton. The fresh weight of rootlet of cotton was affected by any of treatments except the sixth week extract. Study in peteri dish culture proved that among the extracts, the third, the forth and fifth week extracts had the most significant effects on the growth reduction. This is probably due to releasing of some growth inhibitor substance from decomposed rapeseed.

Table 6. Effect of water extracts on growth and germination of cotton

Extract

Germination

Length of hypocotyl

Length of rootlet

Fresh weight of hypocotyl

Dry weight of hypocotyl

Fresh weight of rootlet

Dry weight of rootlet

Non treatment

81.7a

73a

105a

434a

53b

47b

5.1a

First week

80a

60ab

77a

308bc

69a

36d

4.5bc

Second week

80a

56ab

102a

313abc

47c

42bc

5.1a

Third week

80a

39b

68a

282c

40d

29e

3.9d

Forth week

80a

61ab

71a

365abc

52b

41cd

4.9ab

Fifth week

80a

60ab

68a

345abc

54b

37d

a.2cd

Sixth week

80a

71a

97a

424ab

70a

60a

4.4bc

Conclusion

Growing rapeseed as a green manure crop may suppress certain weed species, but could potentially injure succeeding crops. In these studies, cotton was not injured by rapeseed incorporated with soil six week before planting. Small seeded crops may be more susceptible to injury from rapeseed than cotton. (Khatib et al. 1997).growing a rapeseed green manure before planting cotton supports weeds and allow grower to reduce herbicide use or cultivation as needed. The effect of rapeseed planting date, soil moisture and temperature during growth and decay, amount of biomass produced, and time of incorporation on weed suppression all need further study.

References

Boydston RA and Hang A (1995). Rapeseed (Brassica napus) Green manure crop suppresses weeds in potato (Solanum tuberosum). Weed Technology 9,669-675.

Golami A and Mazaheri D (1996).Investigation of allelopathic effect of cover crops on germination and early growth of Sorghum. Fourth Iranian Congress on crop production & breeding science. Sep.3-8, Tabriz University, 198-199.

Leather GR (1983). Weed control using allelopathic crop plants. Journal of Chemical Ecology. 9(8), 31, 983-989.

Khatib KA, Libbey C, Boydston R (1997). Weed suppression with Brassica green manure crops in green pea. Weed Science 45,439-445.

Yamane A, Fujikura J, Ogawa H and Mizutani J (1992). Isothiocyanates as allelopathic compound from Roripa indica Hiern. (Cruciferae) roots. Journal of Chemical Ecology. 18(11), 1941-1954.

Previous PageTop Of PageNext Page