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Evaluation of allelopathic potential among rice (Oryza sativa L.) germplasm for control of Echinochloa crus-galli P. Beauv in the field
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Crop Protection 24 (2005) 413–419 www.elsevier.com/locate/cropro
Evaluation of allelopathic potential among rice (Oryza sativa L.) germplasm for control of Echinochloa crus-galli P. Beauv in the field J.K. Ahn, S.J. Hahn, J.T. Kim, T.D. Khanh, I.M. Chung Department of Applied Life Science, College of Life & Environmental Science, Konkuk University, KwangJinKu HwaYangDong, Seoul 143-701, Republic of Korea Received 1 September 2004; received in revised form 10 September 2004; accepted 13 September 2004
Abstract This study was undertaken to evaluate the allelopathic potential of 78 local Korean rice varieties on the height, leaf area, and straw and leaf dry weights of Echinochloa in a paddy field. Correlations between genetic and morphological characteristics of rice varieties and allelopathic potential were confirmed, with Buldo (56.1%) and Agudo (54.4%) showing the highest average inhibitory effects on barnyard grass. The average inhibition percentage on barnyard grass height, tiller number, total dry weight, straw dry weight, and leaf dry weight ranged from 5.1% to 31.3% depending on the variety. Various characteristics of the varieties showed different allelopathic effects. In crop morphology, there were no differences associated with the presence or absence of an awn, nor with the awn colour. The inhibitory effects for coloured hulls (16.0%) were greater than colourless hulls (23.9%). There was an increasing trend for inhibitory potential from late to early maturity of the variety. These results suggest that the allelopathic potential differed between rice varieties and that genetic and morphological rice characteristics could be used as selection markers for allelopathic rice varieties. r 2004 Elsevier Ltd. All rights reserved. Keywords: Echinochloa; Genetic; Morphological; Characteristics; Variety
1. Introduction Since crop plants were first cultivated, weed control has been an important aspect of their management practices. Although the use of herbicides is a simple and effective method for weed control used worldwide, heavy use of herbicides may cause problems of environmental pollution that affect both animal and human health (Chung et al., 1997; Stephenson, 2000). For this reason, various other methods of weed control have been studied. In particular, the exploitation of allelopathic properties in plants may give promising results (Chung et al., 2003). Allelopathy was was defined by Rice (1984) to mean the direct or indirect harmful or beneficial effects of one plant on another through the Corresponding author. Tel.:+82 2 450 3730; fax:+82 2 446 7856.
E-mail address: [email protected] (I.M. Chung). 0261-2194/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2004.09.009
production of chemical compounds that escape into the environment (Rice, 1984). From the time Dilday et al. (1989, 1991) screened about 12,000 rice accessions or varieties from the USDA/ARS rice germplasm, many scientists have studied the allelopathic potential of rice. These studies of allelopathy mainly involved the screening of the allelopathic potential of rice varieties, the identification of allelochemicals from rice body parts, and the development of new allelopathic varieties (Chou et al., 1991; Garrity et al., 1992; Ahn and Chung, 2000; Chung et al., 2001a, b, 2002; Jung et al., 2004; Lee et al., 2003, 2004; Song et al., 2004). Several researchers developed competition models to evaluate the allelopathic potential between crops and weeds using different methods. Additive methods are designed for when weed populations are added to crop populations, while replacement experiments are based on the assumption that the yield
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of each species in a mixture is proportional to the share of environmental resources it can acquire, and dynamic simulations of competition are based on a hyperbolic relationship between biomass and plant density (Baeumer and DeWit, 1968; Spitters and Van Den Bergh, 1982). Olofsdotter et al. (1999) and Olofsdotter (2001) reported the allelopathic potential of 111 rice cultivars against Echinochloa under field conditions over three seasons in the Philippines and determined that rice height was the most important factor influencing weed suppression. They asserted that allelopathy was more influenced by genetics than the environment. Chung et al. (2003) and Jung et al. (2004) reported the correlations between genetic and morphological characteristics and allelopathic potential. The results of Chung et al. (2003) indicated that domestic varieties, middle-maturing varieties, and varieties with hull and with awn colour had higher inhibitory effects on the germination rate, percentage, and seedling dry weight of barnyard grass. Jung et al. (2004) demonstrated that foreign varieties, middle-maturing, and colourless hull varieties had higher inhibitory effects on the emergence, height, and dry weight of barnyard grass. Song et al. (2004) reported that allelochemicals exuded from rice roots inhibited Echinochloa growth. To date, studies on rice allelopathy have concentrated on the varietal difference of allelopathic potential, biological effects on other plants and weeds, and the isolation and identification of chemicals responsible for allelopathic activities in rice. However, information on rice morphology such as height, tiller number, leaf area, straw dry-weight characteristics and the allelopathic potential of rice has not been described. If the correlation between morphological and genetic characteristics and allelopathic potential of rice could be understood, rice cultivars with strong allelopathic potential might be selected faster and easier. The objective of this study was to evaluate the allelopathic potential of 78 local Korean rice varieties on height, leaf area, and straw and leaf dry weights of barnyard grass in paddy fields and to determine the correlation between morphological and genetic characteristics and allelopathic potential in rice.
characteristics such as maturity time, existence of an awn, and awn and hull colour were examined in each rice variety. 2.2. Additive experiment method and evaluation of allelopathic potential This study was designed as an additive experiment (Baeumer and DeWit, 1968; Spitters and Van Den Bergh, 1982). The 78 rice varieties were grown in seedling boxes for 45 days, and then planted by hand in five 30 cm rows with a 15 cm spacing (30 15 cm per 3.3 m2) between rows. Barnyard grass, grown in seedling boxes for 40 days, were planted in five rows across the rice rows two weeks after they were planted (Fig. 1). No herbicides were used and all other weeds were controlled by band weeding. Fertilizer applications were carried out at a dosage of 110-70-80 (N-P2O5-K2O kg ha1) and pesticides were applied according to the standard methods of rice cultivation in Korea. Barnyard grass, planted separately, served as the control. Allelopathic activity was recorded 67 days after planting based on reductions in height, leaf area, leaf and straw dry weight, and total dry weight. Barnyard grass plants from each row were harvested and the highest extended leaf was recorded as plant height (cm). The leaf area (LA) (cm2 plant1) and dry weight (65 1C oven-dried for 5 days) of leaves and stems were then determined. LA was measured with an automatic area metre (LI-3100 Area metre, LI-COR, Inc., Lincoln, NE, USA), 1000 grain weight was determined (Chung et al., 2001b), and the inhibition percentage was calculated as Inhibition percentage (%)=[(control-rice cultivar)/ control] 100.
30cm
15cm
2. Materials and methods 2.1. Preparation of rice cultivars and barnyard grass Seventy-eight rice varieties, including 143 (PI 274471), and barnyard grass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi) were cultivated and harvested at the Konkuk University experimental farm in 2003. The 78 rice varieties were local Korean varieties and included a popular variety cultivated in Korea, Illpum, which was used as a control. Genetic and morphological
Rice B Barnyardgrass Fig. 1. Diagram of additive experiment method.
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2.3. Statistical analysis The field experiment was conducted twice with a completely randomized design. Analyses of variance were performed for all data using the general linear model procedure (SAS Institute, 1988) and pooled mean values were separated based on least significant differences (LSD) at the 0.05 probability level.
3. Results and discussion 3.1. Evaluation of allelopathic effects on the growth of barnyard grass from 78 rice varieties This study was performed to evaluate the allelopathic potential of 78 rice varieties including 143 (PI 274471) on the height, tiller number, leaf area, and straw, leaf and total dry weights of barnyard grass in the field. Overall, Buldo (56.1%) and Agudo (54.4%) had the highest average inhibitory effects on barnyard grass, and 1000 grain weight of the two varieties were 24.4 and 23.6 g, respectively (Table 1). The average inhibition percentage on barnyard grass height was 5.1%. IRI 301 (Mangkyung) (25.4%) had the highest inhibitory effect on height of the 78 rice varieties, and 13 varieties including Baekhaedal had inhibition rates over 10%. However, 65 varieties had inhibition rates below 10%. The average inhibition percentage on the tiller number was 25.6%, with three varieties including Buldo having percentages of 73.3%. However, 24 varieties including Gangreungdo had inhibitory effects below 10.0%. The average inhibitory effect on leaf area was 29.1%, of which Agudo (79.1%) showed the highest inhibition. Although 15 varieties including Hwangtodo had inhibitory effects greater than 50%, 14 varieties including Gangreungdo were less than 10%. The average inhibitory effect on total dry weight was 21.2%. While Buldo (61.8%) had the highest inhibitory effect, 14 varieties including Namkangbaekjo were less than 10%. The average inhibitory effect on straw dry weight was 19.0%, of which Agudo (68.9%) had the highest inhibitory effect. However, 28 varieties including Cheonggunbyeo were less than 10%. The average inhibitory effect on leaf dry weight was 31.3%. While Buldo (71.6%) and Olbyeo (70.7%) had the highest inhibitory effects, eight varieties including Hwangjo were less than 10% (Table 1). In this study, total dry weight was positively correlated with inhibitions in height (r2 ¼ 0:21 ), tiller number (r2 ¼ 0:71 ), leaf area (r2 ¼ 0:81 ), straw dry weight (r2 ¼ 0:90 ), and leaf dry weight (r2 ¼ 0:90 ). Inhibition of leaf area was positively correlated with tiller number (r2 ¼ 0:78 ) and inhibition of straw dry weight was positively correlated with tiller number (r2 ¼ 0:65 ) and leaf area (r2 ¼ 0:68 ). Inhibition of leaf dry weight was
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positively correlated with tiller number (r2 ¼ 0:62 ), leaf area (r2 ¼ 0:78 ), and straw dry weight (r2 ¼ 0:63 ). These results indicate that the rice varieties might have different allelopathic potentials against barnyard grass, and are supported by several previous reports (Dilday et al., 1994; Olofsdotter et al., 1995; Chung et al., 1997, 2003; Ahn and Chung, 2000). For example, Dilday et al. (1989) screened approximately 5,000 rice varieties for allelopathy against ducksalad (Heteranthera limosa (Sw.) Willd.), of which about 4% demonstrated some allelopathic activity. Jung et al. (2004) reported allelopathic potentials on emergence, height, and dry weight of 51.45%, 39.75%, and 65.13%, respectively, from 114 rice germplasm residues in the laboratory. These results demonstrate that allelopathic varieties had higher inhibitory effects on height and tiller number than non-allelopathic varieties. 3.2. Correlation between plant morphology and allelopathic potential of rice This experiment aimed at determining the correlation between morphological and genetic characteristics and allelopathic potential of rice. The morphological characteristic consisted of the presence or absence of an awn, and the colour of the awn and hull. The genetic characteristic was classified based on time to maturation. 3.2.1. Allelopathic effects with morphological characteristics of the rice varieties The average inhibitory effects with the presence or absence of an awn were 22.5% and 22.7%, respectively, while average inhibitory effects with coloured and colourless awns when the awn was present were 22.8% and 22.2%, respectively. Although the inhibitory effect on leaf dry weight was higher in varieties that possessed an awn, the result was not significant (Table 2). In this study, varieties that possessed an awn (r2 ¼ 0:16 ) and coloured awn varieties (r2 ¼ 0:15 ) were negatively correlated with straw dry weight. This result suggests that coloured awn rice varieties had a lower inhibitory effect on straw growth than varieties that did not possess an awn, a result supported by Chung et al. (2003) and Jung et al. (2004). In particular, Chung et al. (2003) reported that the average inhibition percentages of coloured awn, colourless awn, and awnless varieties were 16.0%, 12.0%, and 14.0%, respectively. They also reported that (1) although selection pressure for nonallelopathic varieties using the phenotype was weak, it would still be valuable to research allelopathic rice varieties based on the characteristic, and (2) high inhibitory effects were correlated with inhibitions of the germination per cent (r2 ¼ 0:89 ) and total dry weight (r2 ¼ 0:77 ) in coloured awn varieties.
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Table 1 Inhibitory effects of 78 rice varieties on the growth of barnyard grass in the paddy field Varieties
143 (PI 274471) Agudo Arongbyeo Badolbyeo Baekchalbyeo Baekgwangok Baekhaedal Baekjicheongbyeo Baekjo Baekkyeongjo Baekmangjo Baekna Bakkye Banchonjo Bandalbyeo Baramdungkuri Boribyeo Buldo Chanarak Cheonggunbyeo Cheongsando Chindadachiki Dabaegjo Dadajo Daegudo Damagung Danganeuibangju Deokjeokjodo Dong o byeo Dongsanjo Donna Dorae Duchungjong Eumseon Eunjo F3-220 Gangcheongdo Gangreungdo Geum chang do Geum jeom do Guando Hambureubyeo3 Heugbal Heugsaekdo Heunbe Hochokjindo Hongdodo Huado Hwangjo Hwangtodo IRI 233 IRI 286 (Nongkwang) IRI 293 (Palgeum) IRI 301 (Mangyung) Jaeraejongna Jangjo Jangsamdo Jangwang Jeokmosaek
1000 grain weight (g)
26.8 23.6 20.4 20.9 25.5 22.3 23.6 25.5 26.9 23.4 27.6 23.5 21.9 21.3 23.4 24.3 20.7 24.4 22.9 26.0 24.0 20.2 22.6 23.1 22.7 22.0 28.8 23.5 25.7 25.3 26.6 25.2 25.3 22.9 21.8 24.8 23.4 25.6 25.5 23.3 22.1 23.9 23.1 23.8 23.8 24.4 21.8 25.6 24.7 24.6 23.8 21.7 28.3 23.8 27.9 26.2 26.9 23.7 23.1
Height
15.5 4.5 0 6.6 8.5 0.8 10.2 10.0 2.6 7.4 5.2 9.1 0.8 6.2 0.2 5.6 19.3 7.1 8.2 0 6.1 9.9 2.3 0 2.5 0 0 18.6 5.2 9.1 0.8 7.4 8.5 0 0 4.2 0 0 0 0 0 22.4 19.1 9.3 22.4 15.5 15.9 6.7 5.6 0 0 0 0 25.4 0 0 3.1 1.6 0
Tiller No.
0 73.3 23.3 3.3 40.0 33.3 33.3 33.3 40.0 36.7 3.3 0 20.0 50.0 63.3 0 36.7 73.3 0 36.7 10.0 36.7 56.7 46.7 30.0 0 3.3 13.3 3.3 0 33.3 36.7 3.3 43.3 23.3 46.7 33.3 6.7 0 56.7 26.7 20.0 33.3 13.3 20.0 0 0 3.3 0 46.7 63.3 73.3 10.0 36.7 60.0 60.0 33.3 33.3 16.7
Leaf area
19.5 79.1 15.4 20.5 33.7 59.6 28.0 46.7 25.9 41.9 13.9 22.6 30.1 45.4 45.3 0 59.0 70.6 11.6 37.9 11.2 46.1 74.2 13.4 1.4 0 24.7 35.0 13.9 22.6 59.6 41.9 19.2 15.8 22.8 44.2 4.0 9.3 0 54.9 10.4 41.0 43.1 25.5 41.0 19.9 0 20.5 0 50.4 36.5 60.6 18.8 52.4 69.5 43.6 24.8 32.3 8.8
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 16.4 68.9 23.5 4.2 28.9 12.7 14.6 51.5 19.9 22.9 0 23.3 0 25.1 30.3 0 20.0 52.0 8.9 6.9 0 33.3 64.5 40.4 0 0 16.2 33.5 0 23.3 12.7 22.9 0 22.5 0.2 16.7 12.0 0 0 65.4 37.2 34.8 14.1 0 34.8 16.4 0 4.2 0 26.9 22.0 12.7 23.3 32.8 46.7 48.8 12.5 35.1 0
30.2 44.1 24.1 26.4 42.7 50.7 36.3 60.4 42.5 44.6 15.7 21.4 30.9 43.9 48.5 5.1 59.0 71.6 13.9 46.4 28.3 43.8 34.3 22.8 16.3 3.4 24.2 31.8 15.7 21.4 50.7 44.6 16.0 18.5 24.6 45.7 17.5 13.0 0 46.7 21.4 54.0 49.0 24.3 54.0 30.2 3.7 26.4 5.1 46.3 25.6 50.7 21.4 31.1 56.6 22.2 12.3 26.4 0
23.3 56.5 23.8 15.3 35.8 31.7 25.5 56.0 31.2 33.7 7.9 22.3 15.4 34.5 39.4 2.5 39.5 61.8 11.4 26.6 14.2 38.5 49.4 31.6 8.2 1.7 20.2 32.6 7.9 22.3 31.7 33.7 8.0 20.5 12.4 31.2 14.7 6.5 0 56.0 29.3 44.4 31.6 12.2 44.4 23.3 1.9 15.3 2.5 36.6 23.8 31.7 22.3 31.9 51.6 35.5 12.4 30.7 0
17.5 54.4 18.4 12.7 31.6 31.5 24.6 43.0 27.0 31.2 7.7 16.5 12.2 34.2 37.8 2.2 38.9 56.1 9.0 25.7 11.6 34.7 46.9 25.8 9.7 0.8 14.8 27.5 7.7 16.5 31.5 31.2 9.2 20.1 13.9 31.5 13.6 5.9 0 46.6 20.8 36.1 31.7 14.1 36.1 17.5 3.6 12.7 2.2 34.5 28.6 38.2 16.0 35.0 47.4 35.0 16.4 26.6 4.3
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Table 1 (continued ) Varieties
1000 grain weight (g)
Height
Tiller No.
Leaf area
Dry weight
Average
Straw
Leaf
Total
Jeona Jeongdaldo Jeongjo Jinhwa Namkangbaekjo Namseon 1 Noindari Noindo Oegukbyeo Olbyeo Patbyeo Pyeongbuk 4 Pyeongyang Sancheongdo Sangpung Sanjo Seogandodo Seungsiljo Sinbaegseog
22.9 24.0 25.4 24.8 21.7 23.2 22.6 20.5 25.0 23.3 22.0 26.2 25.8 25.2 24.9 23.1 23.5 24.7 23.6
0.8 2.6 6.0 0.8 0 0 0 0 0 0 1.91 0 13.9 4.8 11.4 3.7 0 0 4.5
0 0 10.0 0 10.0 16.7 13.3 56.7 46.7 6.7 26.7 46.7 0 43.3 36.7 0 30.0 16.7 3.3
0 10.0 17.1 9.0 0 15.0 18.7 56.2 19.9 16.7 25.1 50.4 24.6 64.3 69.6 18.5 28.8 4.3 3.0
0 0 23.9 10.1 16.1 5.7 0 49.7 23.0 18.1 0 26.9 7.3 42.6 31.2 3.1 0 5.4 26.3
0 10.6 30.2 16.2 1.5 25.6 54.9 43.5 25.8 70.7 27.4 46.3 13.0 66.0 59.9 20.6 25.4 28.4 36.6
0 5.3 27.1 13.1 8.8 15.6 27.4 46.6 24.4 44.4 13.7 36.6 10.2 54.3 45.5 11.9 12.7 16.9 31.4
0 4.8 19.1 8.2 6.1 13.1 19.0 42.1 23.3 26.1 15.8 34.5 11.3 45.9 42.4 9.6 16.2 11.9 17.5
Average
24.0
5.1
25.6
29.1
19.0
31.3
21.2
22.5
2.5
13.9
42.1
42.3
41.2
42.6
39.1
31.8
LSD (0.05)
Table 2 Comparison of allelopathic potential of varieties with and without an awn 1000 grain weight (g)
Height
Tiller No.
Leaf area
Dry weight Straw
Average
Leaf
Total
Inhibition (%) Awn Coloured Colourless Average
24.2 24.2 24.2
6.1 5.0 5.6
24.1 25.6 24.9
29.7 30.0 29.8
17.6 16.0 16.7
33.7 32.5 33.1
25.6 24.6 25.1
22.8 22.2 22.5
Awnless
23.6
4.3
27.1
27.5
24.4
27.2
25.8
22.7
0.8
3.1
10.3
10.1
8.9
9.1
8.2
7.0
LSD (0.05)
The average inhibitory effect of coloured hulls (16.0%) was greater than that of colourless hulls (23.9%). Coloured hull varieties inhibited barnyard grass in all parameters other than for height, with particular significance for tiller number, total dry weight, and straw dry weight (Table 3). In this study, coloured hull varieties were found to be negatively correlated with total dry weight (r2 ¼ 0:17 ), tiller number (r2 ¼ 0:17 ), straw dry weight (r2 ¼ 0:16 ), and leaf dry weight (r2 ¼ 0:14 ). The result of our findings supports previous conclusions by Jung et al. (2004) and Chung et al. (2003) that coloured hull varieties had lower inhibitory effects on straw growth than colourless hull rice varieties.
3.2.2. Correlation between genetic characteristic and allelopathic potential of rice The average inhibition percentages of early, middle, and late maturing varieties were 19.8%, 22.1%, and 25.7%, respectively. However, these results were not significant. According to the inhibitory effect of each maturity group, leaf dry weight had the highest inhibition percentage and the lowest height (Table 4). From our results, maturity was found to be correlated with height, tiller number, and straw dry weight. In particular, late maturing varieties were negatively correlated with height (r2 ¼ 0:25 ), and positively correlated with tiller number (r2 ¼ 0:23 ) and straw dry weight (r2 ¼ 0:15 ). This result was supported by
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Table 3 Comparison of allelopathic potential of varieties with coloured and colourless hulls 1000 grain weight (g)
Coloured hull Colourless hull
Height
Tiller No.
Leaf area
24.3 24.0
6.1 4.9
15.6 27.6
22.8 30.4
0.9
3.4
11.0
10.9
LSD (0.05)
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 10.6 20.7
23.8 32.8
17.2 26.7
16.0 23.9
9.8
8.7
7.5
9.6
Table 4 Comparison of allelopathic potential according to time of maturation 1000 grain weight (g)
Early Middle Late LSD (0.05)
Height
Tiller No.
Leaf area
23.8 24.0 24.3
8.2 3.5 3.5
19.3 23.5 33.8
26.0 27.5 33.7
0.8
3.0
10.0
10.0
Chung et al. (2003), who reported that middle maturing varieties (15.3%) and varieties with hull colour (15.1%) and coloured awns (16.0%) had greater inhibition percentages. Dilday et al. (1989) noted that approximately 191 accessions that demonstrated allelopathic activity also exhibited genetic diversity for plant characteristics such as plant height, maturity, grain type, plant type, hull cover, hull colour, and culm strength. Also, weed suppression score was demonstrated to be highly correlated with weed weight per plot in both the low and moderate weeding treatments (Garrity et al., 1992). Thus, late maturing varieties had lower inhibitory effects on height, but higher inhibitory effects on tiller number and straw dry weight. In this study, our results differ slightly from those of the previous reports (Chung et al., 2000, 2003; Jung et al., 2004) with regard to the allelopathic potential of rice germplasm. For example, Chung et al. (2000) reported that Seogandodo (67.07%) had the highest inhibition percentage among 79 local Korean varieties with rice straw mixture in the green house study. However, Seogandodo only showed a 16.2% inhibitory effect in this study (Table 1). Allelopathy and competition are also clearly related in the field although their mechanisms are distinct. Growth inhibition by allelopathy would be expected to reduce the competitive ability of the inhibited plant. Thus, differential activity including both inhibitory and stimulatory relationships between field and laboratory study would be expected.
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 14.3 20.2 22.7
29.2 31.9 32.9
21.7 26.1 27.8
19.8 22.1 25.7
9.1
8.1
6.9
8.8
In conclusion, the objective of this study was to evaluate the allelopathic potential on barnyard grass from rice germplasm in paddy fields and to correlate genetic and morphological characteristics of rice varieties with allelopathic potential. It is difficult to select from allelopathic varieties in rice germplasm because allelopathic potential consists of complex reactions between the plant and several conditions such as water stress, temperature, light, plant age, and soil. If the correlation between morphological and genetic characteristics and allelopathic potential of rice could be understood, rice cultivars with strong allelopathic potential might be selected faster and easier. Our findings from this study suggest that allelopathic potential varied among rice variety and that morphological and genetic characteristics might be used as selection markers for allelopathic rice varieties. The effective utilization of genetic variation for weedinhibition ability in rice would depend on whether the genetic variation was sufficiently broad because the trait had a large negative relationship with grain yield potential. Genotypes could be screened for the trait in a practical manner. However, more experiments between rice and weed plants and investigations of more genetic and morphological characteristics using a larger number of rice varieties are needed. In addition, further examination of the field experimental design should be made, as additive and replacement designs are required to select allelopathic varieties under field conditions.
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Further investigation is needed to analyse any inhibitory substances in the varietal variation.
Acknowledgements The authors wish to acknowledge the financial support of the Rural Development Administration made to the BioGreen 21 in 2003. References Ahn, J.K., Chung, I.M., 2000. Allelopathic potential of rice hulls on germination and seedling growth of barnyardgrass. Agron. J. 92, 1162–1167. Baeumer, K., DeWit, C.T., 1968. Competitive interference of plant species in monoculture and mixed stands. Neth. J. Agric. Sci. 16, 103–122. Chou, C.H., Chang, F.J., Oka, H.I., 1991. Allelopathic potentials of wild rice Oryza perennis. Taiwania 36, 201–210. Chung, I.M., Kim, K.H., Ahn, J.K., Ju, H.J., 1997. Allelopathic potential of rice varieties on Echinochloa crus-galli. Korean J. Weed Sci. 17, 52–58. Chung, I.M., Ahn, J.K., Kim, J.T., Kim, C.S., 2000. Assessment of allelopathic potentiality and identification of allelopathic compounds on Korean local varieties. Korean J. Crop Sci. 45, 44–49. Chung, I.M., Ahn, J.K., Yun, S.J., 2001a. Identification of allelopathic compounds from rice (Oryza sativa L.) straw and their biological activity. Can. J. Plant Sci. 81, 815–819. Chung, I.M., Ahn, J.K., Yun, S.J., 2001b. Assessment of allelopathic potential of barnyardgrass (Echinochloa crus-galli) on rice (Oryza sativa L.) cultivars. Crop Prot 20, 921–928. Chung, I.M., Kim, K.H., Ahn, J.K., Chun, S.C., Kim, C.S., Kim, J.T., Kim, S.H., 2002. Screening of allelochemicals on barnyardgrass (Echinochloa crus-galli) and identification of potentially allelopathic compounds from rice (Oryza sativa) variety hull extracts. Crop Prot 21, 913–920. Chung, I.M., Kim, K.H., Ahn, J.K., Lee, S.B., Kim, S.H., Hahn, S.J., 2003. Comparison of allelopathic potential of rice leaves, straw, and hull extracts on barnyardgrass. Agron. J. 95, 1063–1070. Dilday, R.H., Nastasi, P., Smith Jr., R.J., 1989. Potential allelopathic activity of rice (Oryza sativa L.) germplasm. Proceedings of the
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42nd Annual Meeting of the Southern Weed Science Society, p. 261. Dilday, R.H., Nastasi, P., Li, J., Smith Jr., R.J., 1991. Allelopathy activity in rice (Oryza sativa L.) against ducksalad (Heteranthera limosa (Sw.)). In: Sustainable Agriculture for the Great Plains, Symposium proceedings, US Department of Agriculture, pp. 193–201. Dilday, R.H., Lin, J., Yan, W., 1994. Identification of allelopathy in the USDA-ARS rice germplasm collection. Aust. J. Exp. Agr. 34, 907–910. Garrity, D.P., Movillon, M., Moody, K., 1992. Differential weed suppression ability in upland rice cultivars. Agron. J. 84, 586–591. Jung, W.S., Kim, K.H., Ahn, J.K., Hahn, S.J., Chung, I.M., 2004. Allelopathic potential of rice (Oryza sativa L.) residues against Echinochloa crus-galli. Crop Prot. 23, 211–218. Lee, S.B., Kim, K.H., Hahn, S.J., Chung, I.M., 2003. Evaluation of screening methods to determine the allelopathic potential of rice varieties against Echinochloa crus-galli Beauv. var. oryzicola Ohwi. Allelopathy J 12, 37–52. Lee, S.B., Ku, Y.C., Kim, K.H., Hahn, S.J., Chung, I.M., 2004. Allelopathic potential of rice germplasm against barnyardgrass. Allelopathy J 13, 17–28. Olofsdotter, M., 2001. Rice—a step toward use of allelopathy. Agron. J. 39, 3–8. Olofsdotter, M., Navarez, K., Moody, K., 1995. Allelopathic potential in rice (Oryza sativa L.). Ann. Appl. Biol. 127, 543–560. Olofsdotter, M., Navarez, D., Rebulanan, M., Streibig, J.C., 1999. Weed-suppressing rice cultivars—does allelopathy play a role? Weed Res 39, 441–454. Rice, E.L., 1984. Allelopathy, Second ed. Academic Press, Orlando, FL. SAS Institute, 1988. SAS/STAT User’s Guide, 6.03 ed. SAS Inst., Cary, NC. Song, H.K., Ahn, J.K., Ahmad, A., Hahn, S.J., Kim, S.H., Chung, I.M., 2004. Identification of allelochemicals in rice exudates at various phenological phases and their influence on barnyard grass. Allelopathy J 13, 173–188. Spitters, C.J.T., Van Den Bergh, J.P., 1982. Competition between crop and weeds: a system approach. In: Holzner, W., Numata, N. (Eds.), Biology and Ecology of Weeds. W. Junk, The Hague, pp. 137–148. Stephenson, G.R., 2000. Herbicide use and world food production: risks and benefits. In: Legere, A. (Ed.), Abstracts of III International Weed Science Congress, Foz do Iguassu, Brazil, 6–11 June 2000. International Weed Science Society, Corvallis, OR, p. 248.
Crop Protection 24 (2005) 413–419 www.elsevier.com/locate/cropro
Evaluation of allelopathic potential among rice (Oryza sativa L.) germplasm for control of Echinochloa crus-galli P. Beauv in the field J.K. Ahn, S.J. Hahn, J.T. Kim, T.D. Khanh, I.M. Chung Department of Applied Life Science, College of Life & Environmental Science, Konkuk University, KwangJinKu HwaYangDong, Seoul 143-701, Republic of Korea Received 1 September 2004; received in revised form 10 September 2004; accepted 13 September 2004
Abstract This study was undertaken to evaluate the allelopathic potential of 78 local Korean rice varieties on the height, leaf area, and straw and leaf dry weights of Echinochloa in a paddy field. Correlations between genetic and morphological characteristics of rice varieties and allelopathic potential were confirmed, with Buldo (56.1%) and Agudo (54.4%) showing the highest average inhibitory effects on barnyard grass. The average inhibition percentage on barnyard grass height, tiller number, total dry weight, straw dry weight, and leaf dry weight ranged from 5.1% to 31.3% depending on the variety. Various characteristics of the varieties showed different allelopathic effects. In crop morphology, there were no differences associated with the presence or absence of an awn, nor with the awn colour. The inhibitory effects for coloured hulls (16.0%) were greater than colourless hulls (23.9%). There was an increasing trend for inhibitory potential from late to early maturity of the variety. These results suggest that the allelopathic potential differed between rice varieties and that genetic and morphological rice characteristics could be used as selection markers for allelopathic rice varieties. r 2004 Elsevier Ltd. All rights reserved. Keywords: Echinochloa; Genetic; Morphological; Characteristics; Variety
1. Introduction Since crop plants were first cultivated, weed control has been an important aspect of their management practices. Although the use of herbicides is a simple and effective method for weed control used worldwide, heavy use of herbicides may cause problems of environmental pollution that affect both animal and human health (Chung et al., 1997; Stephenson, 2000). For this reason, various other methods of weed control have been studied. In particular, the exploitation of allelopathic properties in plants may give promising results (Chung et al., 2003). Allelopathy was was defined by Rice (1984) to mean the direct or indirect harmful or beneficial effects of one plant on another through the Corresponding author. Tel.:+82 2 450 3730; fax:+82 2 446 7856.
E-mail address: [email protected] (I.M. Chung). 0261-2194/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2004.09.009
production of chemical compounds that escape into the environment (Rice, 1984). From the time Dilday et al. (1989, 1991) screened about 12,000 rice accessions or varieties from the USDA/ARS rice germplasm, many scientists have studied the allelopathic potential of rice. These studies of allelopathy mainly involved the screening of the allelopathic potential of rice varieties, the identification of allelochemicals from rice body parts, and the development of new allelopathic varieties (Chou et al., 1991; Garrity et al., 1992; Ahn and Chung, 2000; Chung et al., 2001a, b, 2002; Jung et al., 2004; Lee et al., 2003, 2004; Song et al., 2004). Several researchers developed competition models to evaluate the allelopathic potential between crops and weeds using different methods. Additive methods are designed for when weed populations are added to crop populations, while replacement experiments are based on the assumption that the yield
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of each species in a mixture is proportional to the share of environmental resources it can acquire, and dynamic simulations of competition are based on a hyperbolic relationship between biomass and plant density (Baeumer and DeWit, 1968; Spitters and Van Den Bergh, 1982). Olofsdotter et al. (1999) and Olofsdotter (2001) reported the allelopathic potential of 111 rice cultivars against Echinochloa under field conditions over three seasons in the Philippines and determined that rice height was the most important factor influencing weed suppression. They asserted that allelopathy was more influenced by genetics than the environment. Chung et al. (2003) and Jung et al. (2004) reported the correlations between genetic and morphological characteristics and allelopathic potential. The results of Chung et al. (2003) indicated that domestic varieties, middle-maturing varieties, and varieties with hull and with awn colour had higher inhibitory effects on the germination rate, percentage, and seedling dry weight of barnyard grass. Jung et al. (2004) demonstrated that foreign varieties, middle-maturing, and colourless hull varieties had higher inhibitory effects on the emergence, height, and dry weight of barnyard grass. Song et al. (2004) reported that allelochemicals exuded from rice roots inhibited Echinochloa growth. To date, studies on rice allelopathy have concentrated on the varietal difference of allelopathic potential, biological effects on other plants and weeds, and the isolation and identification of chemicals responsible for allelopathic activities in rice. However, information on rice morphology such as height, tiller number, leaf area, straw dry-weight characteristics and the allelopathic potential of rice has not been described. If the correlation between morphological and genetic characteristics and allelopathic potential of rice could be understood, rice cultivars with strong allelopathic potential might be selected faster and easier. The objective of this study was to evaluate the allelopathic potential of 78 local Korean rice varieties on height, leaf area, and straw and leaf dry weights of barnyard grass in paddy fields and to determine the correlation between morphological and genetic characteristics and allelopathic potential in rice.
characteristics such as maturity time, existence of an awn, and awn and hull colour were examined in each rice variety. 2.2. Additive experiment method and evaluation of allelopathic potential This study was designed as an additive experiment (Baeumer and DeWit, 1968; Spitters and Van Den Bergh, 1982). The 78 rice varieties were grown in seedling boxes for 45 days, and then planted by hand in five 30 cm rows with a 15 cm spacing (30 15 cm per 3.3 m2) between rows. Barnyard grass, grown in seedling boxes for 40 days, were planted in five rows across the rice rows two weeks after they were planted (Fig. 1). No herbicides were used and all other weeds were controlled by band weeding. Fertilizer applications were carried out at a dosage of 110-70-80 (N-P2O5-K2O kg ha1) and pesticides were applied according to the standard methods of rice cultivation in Korea. Barnyard grass, planted separately, served as the control. Allelopathic activity was recorded 67 days after planting based on reductions in height, leaf area, leaf and straw dry weight, and total dry weight. Barnyard grass plants from each row were harvested and the highest extended leaf was recorded as plant height (cm). The leaf area (LA) (cm2 plant1) and dry weight (65 1C oven-dried for 5 days) of leaves and stems were then determined. LA was measured with an automatic area metre (LI-3100 Area metre, LI-COR, Inc., Lincoln, NE, USA), 1000 grain weight was determined (Chung et al., 2001b), and the inhibition percentage was calculated as Inhibition percentage (%)=[(control-rice cultivar)/ control] 100.
30cm
15cm
2. Materials and methods 2.1. Preparation of rice cultivars and barnyard grass Seventy-eight rice varieties, including 143 (PI 274471), and barnyard grass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi) were cultivated and harvested at the Konkuk University experimental farm in 2003. The 78 rice varieties were local Korean varieties and included a popular variety cultivated in Korea, Illpum, which was used as a control. Genetic and morphological
Rice B Barnyardgrass Fig. 1. Diagram of additive experiment method.
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2.3. Statistical analysis The field experiment was conducted twice with a completely randomized design. Analyses of variance were performed for all data using the general linear model procedure (SAS Institute, 1988) and pooled mean values were separated based on least significant differences (LSD) at the 0.05 probability level.
3. Results and discussion 3.1. Evaluation of allelopathic effects on the growth of barnyard grass from 78 rice varieties This study was performed to evaluate the allelopathic potential of 78 rice varieties including 143 (PI 274471) on the height, tiller number, leaf area, and straw, leaf and total dry weights of barnyard grass in the field. Overall, Buldo (56.1%) and Agudo (54.4%) had the highest average inhibitory effects on barnyard grass, and 1000 grain weight of the two varieties were 24.4 and 23.6 g, respectively (Table 1). The average inhibition percentage on barnyard grass height was 5.1%. IRI 301 (Mangkyung) (25.4%) had the highest inhibitory effect on height of the 78 rice varieties, and 13 varieties including Baekhaedal had inhibition rates over 10%. However, 65 varieties had inhibition rates below 10%. The average inhibition percentage on the tiller number was 25.6%, with three varieties including Buldo having percentages of 73.3%. However, 24 varieties including Gangreungdo had inhibitory effects below 10.0%. The average inhibitory effect on leaf area was 29.1%, of which Agudo (79.1%) showed the highest inhibition. Although 15 varieties including Hwangtodo had inhibitory effects greater than 50%, 14 varieties including Gangreungdo were less than 10%. The average inhibitory effect on total dry weight was 21.2%. While Buldo (61.8%) had the highest inhibitory effect, 14 varieties including Namkangbaekjo were less than 10%. The average inhibitory effect on straw dry weight was 19.0%, of which Agudo (68.9%) had the highest inhibitory effect. However, 28 varieties including Cheonggunbyeo were less than 10%. The average inhibitory effect on leaf dry weight was 31.3%. While Buldo (71.6%) and Olbyeo (70.7%) had the highest inhibitory effects, eight varieties including Hwangjo were less than 10% (Table 1). In this study, total dry weight was positively correlated with inhibitions in height (r2 ¼ 0:21 ), tiller number (r2 ¼ 0:71 ), leaf area (r2 ¼ 0:81 ), straw dry weight (r2 ¼ 0:90 ), and leaf dry weight (r2 ¼ 0:90 ). Inhibition of leaf area was positively correlated with tiller number (r2 ¼ 0:78 ) and inhibition of straw dry weight was positively correlated with tiller number (r2 ¼ 0:65 ) and leaf area (r2 ¼ 0:68 ). Inhibition of leaf dry weight was
415
positively correlated with tiller number (r2 ¼ 0:62 ), leaf area (r2 ¼ 0:78 ), and straw dry weight (r2 ¼ 0:63 ). These results indicate that the rice varieties might have different allelopathic potentials against barnyard grass, and are supported by several previous reports (Dilday et al., 1994; Olofsdotter et al., 1995; Chung et al., 1997, 2003; Ahn and Chung, 2000). For example, Dilday et al. (1989) screened approximately 5,000 rice varieties for allelopathy against ducksalad (Heteranthera limosa (Sw.) Willd.), of which about 4% demonstrated some allelopathic activity. Jung et al. (2004) reported allelopathic potentials on emergence, height, and dry weight of 51.45%, 39.75%, and 65.13%, respectively, from 114 rice germplasm residues in the laboratory. These results demonstrate that allelopathic varieties had higher inhibitory effects on height and tiller number than non-allelopathic varieties. 3.2. Correlation between plant morphology and allelopathic potential of rice This experiment aimed at determining the correlation between morphological and genetic characteristics and allelopathic potential of rice. The morphological characteristic consisted of the presence or absence of an awn, and the colour of the awn and hull. The genetic characteristic was classified based on time to maturation. 3.2.1. Allelopathic effects with morphological characteristics of the rice varieties The average inhibitory effects with the presence or absence of an awn were 22.5% and 22.7%, respectively, while average inhibitory effects with coloured and colourless awns when the awn was present were 22.8% and 22.2%, respectively. Although the inhibitory effect on leaf dry weight was higher in varieties that possessed an awn, the result was not significant (Table 2). In this study, varieties that possessed an awn (r2 ¼ 0:16 ) and coloured awn varieties (r2 ¼ 0:15 ) were negatively correlated with straw dry weight. This result suggests that coloured awn rice varieties had a lower inhibitory effect on straw growth than varieties that did not possess an awn, a result supported by Chung et al. (2003) and Jung et al. (2004). In particular, Chung et al. (2003) reported that the average inhibition percentages of coloured awn, colourless awn, and awnless varieties were 16.0%, 12.0%, and 14.0%, respectively. They also reported that (1) although selection pressure for nonallelopathic varieties using the phenotype was weak, it would still be valuable to research allelopathic rice varieties based on the characteristic, and (2) high inhibitory effects were correlated with inhibitions of the germination per cent (r2 ¼ 0:89 ) and total dry weight (r2 ¼ 0:77 ) in coloured awn varieties.
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Table 1 Inhibitory effects of 78 rice varieties on the growth of barnyard grass in the paddy field Varieties
143 (PI 274471) Agudo Arongbyeo Badolbyeo Baekchalbyeo Baekgwangok Baekhaedal Baekjicheongbyeo Baekjo Baekkyeongjo Baekmangjo Baekna Bakkye Banchonjo Bandalbyeo Baramdungkuri Boribyeo Buldo Chanarak Cheonggunbyeo Cheongsando Chindadachiki Dabaegjo Dadajo Daegudo Damagung Danganeuibangju Deokjeokjodo Dong o byeo Dongsanjo Donna Dorae Duchungjong Eumseon Eunjo F3-220 Gangcheongdo Gangreungdo Geum chang do Geum jeom do Guando Hambureubyeo3 Heugbal Heugsaekdo Heunbe Hochokjindo Hongdodo Huado Hwangjo Hwangtodo IRI 233 IRI 286 (Nongkwang) IRI 293 (Palgeum) IRI 301 (Mangyung) Jaeraejongna Jangjo Jangsamdo Jangwang Jeokmosaek
1000 grain weight (g)
26.8 23.6 20.4 20.9 25.5 22.3 23.6 25.5 26.9 23.4 27.6 23.5 21.9 21.3 23.4 24.3 20.7 24.4 22.9 26.0 24.0 20.2 22.6 23.1 22.7 22.0 28.8 23.5 25.7 25.3 26.6 25.2 25.3 22.9 21.8 24.8 23.4 25.6 25.5 23.3 22.1 23.9 23.1 23.8 23.8 24.4 21.8 25.6 24.7 24.6 23.8 21.7 28.3 23.8 27.9 26.2 26.9 23.7 23.1
Height
15.5 4.5 0 6.6 8.5 0.8 10.2 10.0 2.6 7.4 5.2 9.1 0.8 6.2 0.2 5.6 19.3 7.1 8.2 0 6.1 9.9 2.3 0 2.5 0 0 18.6 5.2 9.1 0.8 7.4 8.5 0 0 4.2 0 0 0 0 0 22.4 19.1 9.3 22.4 15.5 15.9 6.7 5.6 0 0 0 0 25.4 0 0 3.1 1.6 0
Tiller No.
0 73.3 23.3 3.3 40.0 33.3 33.3 33.3 40.0 36.7 3.3 0 20.0 50.0 63.3 0 36.7 73.3 0 36.7 10.0 36.7 56.7 46.7 30.0 0 3.3 13.3 3.3 0 33.3 36.7 3.3 43.3 23.3 46.7 33.3 6.7 0 56.7 26.7 20.0 33.3 13.3 20.0 0 0 3.3 0 46.7 63.3 73.3 10.0 36.7 60.0 60.0 33.3 33.3 16.7
Leaf area
19.5 79.1 15.4 20.5 33.7 59.6 28.0 46.7 25.9 41.9 13.9 22.6 30.1 45.4 45.3 0 59.0 70.6 11.6 37.9 11.2 46.1 74.2 13.4 1.4 0 24.7 35.0 13.9 22.6 59.6 41.9 19.2 15.8 22.8 44.2 4.0 9.3 0 54.9 10.4 41.0 43.1 25.5 41.0 19.9 0 20.5 0 50.4 36.5 60.6 18.8 52.4 69.5 43.6 24.8 32.3 8.8
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 16.4 68.9 23.5 4.2 28.9 12.7 14.6 51.5 19.9 22.9 0 23.3 0 25.1 30.3 0 20.0 52.0 8.9 6.9 0 33.3 64.5 40.4 0 0 16.2 33.5 0 23.3 12.7 22.9 0 22.5 0.2 16.7 12.0 0 0 65.4 37.2 34.8 14.1 0 34.8 16.4 0 4.2 0 26.9 22.0 12.7 23.3 32.8 46.7 48.8 12.5 35.1 0
30.2 44.1 24.1 26.4 42.7 50.7 36.3 60.4 42.5 44.6 15.7 21.4 30.9 43.9 48.5 5.1 59.0 71.6 13.9 46.4 28.3 43.8 34.3 22.8 16.3 3.4 24.2 31.8 15.7 21.4 50.7 44.6 16.0 18.5 24.6 45.7 17.5 13.0 0 46.7 21.4 54.0 49.0 24.3 54.0 30.2 3.7 26.4 5.1 46.3 25.6 50.7 21.4 31.1 56.6 22.2 12.3 26.4 0
23.3 56.5 23.8 15.3 35.8 31.7 25.5 56.0 31.2 33.7 7.9 22.3 15.4 34.5 39.4 2.5 39.5 61.8 11.4 26.6 14.2 38.5 49.4 31.6 8.2 1.7 20.2 32.6 7.9 22.3 31.7 33.7 8.0 20.5 12.4 31.2 14.7 6.5 0 56.0 29.3 44.4 31.6 12.2 44.4 23.3 1.9 15.3 2.5 36.6 23.8 31.7 22.3 31.9 51.6 35.5 12.4 30.7 0
17.5 54.4 18.4 12.7 31.6 31.5 24.6 43.0 27.0 31.2 7.7 16.5 12.2 34.2 37.8 2.2 38.9 56.1 9.0 25.7 11.6 34.7 46.9 25.8 9.7 0.8 14.8 27.5 7.7 16.5 31.5 31.2 9.2 20.1 13.9 31.5 13.6 5.9 0 46.6 20.8 36.1 31.7 14.1 36.1 17.5 3.6 12.7 2.2 34.5 28.6 38.2 16.0 35.0 47.4 35.0 16.4 26.6 4.3
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Table 1 (continued ) Varieties
1000 grain weight (g)
Height
Tiller No.
Leaf area
Dry weight
Average
Straw
Leaf
Total
Jeona Jeongdaldo Jeongjo Jinhwa Namkangbaekjo Namseon 1 Noindari Noindo Oegukbyeo Olbyeo Patbyeo Pyeongbuk 4 Pyeongyang Sancheongdo Sangpung Sanjo Seogandodo Seungsiljo Sinbaegseog
22.9 24.0 25.4 24.8 21.7 23.2 22.6 20.5 25.0 23.3 22.0 26.2 25.8 25.2 24.9 23.1 23.5 24.7 23.6
0.8 2.6 6.0 0.8 0 0 0 0 0 0 1.91 0 13.9 4.8 11.4 3.7 0 0 4.5
0 0 10.0 0 10.0 16.7 13.3 56.7 46.7 6.7 26.7 46.7 0 43.3 36.7 0 30.0 16.7 3.3
0 10.0 17.1 9.0 0 15.0 18.7 56.2 19.9 16.7 25.1 50.4 24.6 64.3 69.6 18.5 28.8 4.3 3.0
0 0 23.9 10.1 16.1 5.7 0 49.7 23.0 18.1 0 26.9 7.3 42.6 31.2 3.1 0 5.4 26.3
0 10.6 30.2 16.2 1.5 25.6 54.9 43.5 25.8 70.7 27.4 46.3 13.0 66.0 59.9 20.6 25.4 28.4 36.6
0 5.3 27.1 13.1 8.8 15.6 27.4 46.6 24.4 44.4 13.7 36.6 10.2 54.3 45.5 11.9 12.7 16.9 31.4
0 4.8 19.1 8.2 6.1 13.1 19.0 42.1 23.3 26.1 15.8 34.5 11.3 45.9 42.4 9.6 16.2 11.9 17.5
Average
24.0
5.1
25.6
29.1
19.0
31.3
21.2
22.5
2.5
13.9
42.1
42.3
41.2
42.6
39.1
31.8
LSD (0.05)
Table 2 Comparison of allelopathic potential of varieties with and without an awn 1000 grain weight (g)
Height
Tiller No.
Leaf area
Dry weight Straw
Average
Leaf
Total
Inhibition (%) Awn Coloured Colourless Average
24.2 24.2 24.2
6.1 5.0 5.6
24.1 25.6 24.9
29.7 30.0 29.8
17.6 16.0 16.7
33.7 32.5 33.1
25.6 24.6 25.1
22.8 22.2 22.5
Awnless
23.6
4.3
27.1
27.5
24.4
27.2
25.8
22.7
0.8
3.1
10.3
10.1
8.9
9.1
8.2
7.0
LSD (0.05)
The average inhibitory effect of coloured hulls (16.0%) was greater than that of colourless hulls (23.9%). Coloured hull varieties inhibited barnyard grass in all parameters other than for height, with particular significance for tiller number, total dry weight, and straw dry weight (Table 3). In this study, coloured hull varieties were found to be negatively correlated with total dry weight (r2 ¼ 0:17 ), tiller number (r2 ¼ 0:17 ), straw dry weight (r2 ¼ 0:16 ), and leaf dry weight (r2 ¼ 0:14 ). The result of our findings supports previous conclusions by Jung et al. (2004) and Chung et al. (2003) that coloured hull varieties had lower inhibitory effects on straw growth than colourless hull rice varieties.
3.2.2. Correlation between genetic characteristic and allelopathic potential of rice The average inhibition percentages of early, middle, and late maturing varieties were 19.8%, 22.1%, and 25.7%, respectively. However, these results were not significant. According to the inhibitory effect of each maturity group, leaf dry weight had the highest inhibition percentage and the lowest height (Table 4). From our results, maturity was found to be correlated with height, tiller number, and straw dry weight. In particular, late maturing varieties were negatively correlated with height (r2 ¼ 0:25 ), and positively correlated with tiller number (r2 ¼ 0:23 ) and straw dry weight (r2 ¼ 0:15 ). This result was supported by
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Table 3 Comparison of allelopathic potential of varieties with coloured and colourless hulls 1000 grain weight (g)
Coloured hull Colourless hull
Height
Tiller No.
Leaf area
24.3 24.0
6.1 4.9
15.6 27.6
22.8 30.4
0.9
3.4
11.0
10.9
LSD (0.05)
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 10.6 20.7
23.8 32.8
17.2 26.7
16.0 23.9
9.8
8.7
7.5
9.6
Table 4 Comparison of allelopathic potential according to time of maturation 1000 grain weight (g)
Early Middle Late LSD (0.05)
Height
Tiller No.
Leaf area
23.8 24.0 24.3
8.2 3.5 3.5
19.3 23.5 33.8
26.0 27.5 33.7
0.8
3.0
10.0
10.0
Chung et al. (2003), who reported that middle maturing varieties (15.3%) and varieties with hull colour (15.1%) and coloured awns (16.0%) had greater inhibition percentages. Dilday et al. (1989) noted that approximately 191 accessions that demonstrated allelopathic activity also exhibited genetic diversity for plant characteristics such as plant height, maturity, grain type, plant type, hull cover, hull colour, and culm strength. Also, weed suppression score was demonstrated to be highly correlated with weed weight per plot in both the low and moderate weeding treatments (Garrity et al., 1992). Thus, late maturing varieties had lower inhibitory effects on height, but higher inhibitory effects on tiller number and straw dry weight. In this study, our results differ slightly from those of the previous reports (Chung et al., 2000, 2003; Jung et al., 2004) with regard to the allelopathic potential of rice germplasm. For example, Chung et al. (2000) reported that Seogandodo (67.07%) had the highest inhibition percentage among 79 local Korean varieties with rice straw mixture in the green house study. However, Seogandodo only showed a 16.2% inhibitory effect in this study (Table 1). Allelopathy and competition are also clearly related in the field although their mechanisms are distinct. Growth inhibition by allelopathy would be expected to reduce the competitive ability of the inhibited plant. Thus, differential activity including both inhibitory and stimulatory relationships between field and laboratory study would be expected.
Dry weight
Average
Straw
Leaf
Total
Inhibition (%) 14.3 20.2 22.7
29.2 31.9 32.9
21.7 26.1 27.8
19.8 22.1 25.7
9.1
8.1
6.9
8.8
In conclusion, the objective of this study was to evaluate the allelopathic potential on barnyard grass from rice germplasm in paddy fields and to correlate genetic and morphological characteristics of rice varieties with allelopathic potential. It is difficult to select from allelopathic varieties in rice germplasm because allelopathic potential consists of complex reactions between the plant and several conditions such as water stress, temperature, light, plant age, and soil. If the correlation between morphological and genetic characteristics and allelopathic potential of rice could be understood, rice cultivars with strong allelopathic potential might be selected faster and easier. Our findings from this study suggest that allelopathic potential varied among rice variety and that morphological and genetic characteristics might be used as selection markers for allelopathic rice varieties. The effective utilization of genetic variation for weedinhibition ability in rice would depend on whether the genetic variation was sufficiently broad because the trait had a large negative relationship with grain yield potential. Genotypes could be screened for the trait in a practical manner. However, more experiments between rice and weed plants and investigations of more genetic and morphological characteristics using a larger number of rice varieties are needed. In addition, further examination of the field experimental design should be made, as additive and replacement designs are required to select allelopathic varieties under field conditions.
ARTICLE IN PRESS J.K. Ahn et al. / Crop Protection 24 (2005) 413–419
Further investigation is needed to analyse any inhibitory substances in the varietal variation.
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