Study of allelopathic interference of rapeseed (Brassica napus var.belinda) on germination and growth of cotton (Gossypium hirsutum) and it’s dominant weeds
Department of Plant Pests and Diseases - Agricultural Research Center of Golestan province-Gorgan-Iran
E-mail myounesabadi@yahoo.com
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.
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 ºC. 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 |
42ª |
11.7a |
16a |
9a |
1.5 |
None |
39ab |
728ab |
62b |
6.71ab |
0.82b |
41.8ª |
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 |
40.3ª |
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.