Allelopathic potential of rice (Oryza sativa L.) residues against Echinochloa crus-galli

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Crop Protection 23 (2004) 211–218

Allelopathic potential of rice (Oryza sativa L.) residues against Echinochloa crus-galli W.S. Junga, K.H. Kima, J.K. Ahnb, S.J. Hahna, I.M. Chungb,* b

a Department of Crop Science, Konkuk University, Seoul 143-701, South Korea Research Team of Friendly Environmental Low Input Natural Herbicide New Material Study, Konkuk University, Seoul 143-701, South Korea

Received 17 July 2003; received in revised form 25 August 2003; accepted 28 August 2003

Abstract This bioassay was conducted to examine the allelopathic effects of different parts of rice plants, and the genetic and phenotypic characters of rice varieties, on Echinochloa crus-galli P.Beauv.var.oryzi-cola Ohwi. The average inhibition by the variety Duchungjong on E. crus-galli (77.7%) was higher than the inhibition by other varieties. The inhibitory effect on emergence induced by a leaves-plus-straw mixture was extremely high for the Damagung strain (95.9%). Daegudo showed the highest percentage inhibition (93.2%) by hull residues. The leaves-plus-straw mixture and hull residue of Basmati showed the highest percentage inhibition on plant height (75.7% and 66.7%, respectively). The leaves-plus-straw mixture and hull residue of Damagung exhibited the highest percentage inhibition of aboveground dry weight (98% and 97.1%, respectively). The greatest inhibition of aboveground and root dry weight by a hull residue was produced by Kasarwala mundara (95.6% and 94.3%, respectively). In terms of origin, foreign varieties showed a greater percentage inhibition (61%) than domestic varieties (52.4%). Rice varieties with intermediate maturing times showed a greater percentage inhibition (59.3%) than other varieties (early maturing 50.2% and late maturing 56.1%). Coloured hulls showed 55.9% inhibition, whereas colourless hulls showed 65.4% inhibition. Awnless, colourless-awn, and coloured-awn groups did not differ significantly in average inhibition (55.6%, 55%, and 53.5%, respectively). r 2003 Elsevier Ltd. All rights reserved. Keywords: Allelopathy; Residue; Oryza sativa; Echinochloa crus-galli

1. Introduction The cultivation of rice (Oryza sativa L.), which has long been grown as an annual summer food crop in Korea, is characterized by the heavy use of fertilizers, herbicides, and pesticides. Stephenson (2000) calculated that most agricultural systems collectively used three million tons of herbicide per year. Furthermore, Chung et al. (2001) reported that direct-seeded rice usage is expected to increase and will have a greater reliance on herbicides for weed management. In Korea, Echinochloa crus-galli P. Beauv. var. oryzi-cola Ohwi (barnyardgrass) is one of the most successful yield-limiting weeds (57–95%) in irrigated rice systems during the cropping season (Ahn and Chung, 2000). The increasing use of herbicides *Corresponding author. Research Team of Friendly Environmental Low Input Natural Herbicide New Material Study, Konkuk University, KwangJinKu MoJinDong, Seoul 143-701 South Korea. Tel.: +82-2-450-3730; fax: +82-2-446-7856. E-mail address: [email protected] (I.M. Chung). 0261-2194/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2003.08.019

for weed management may pollute the water and soils in paddy ecosystems. Therefore, other managements systems are required for the control of barnyardgrass, and allelopathy has been suggested. The allelopathic potential of rice was first ascertained by Dilday et al. (1989) in the USA, since which time the International Rice Research Institute (IRRI), Japan, and Korea have been actively studying rice allelopathy. Known allelochemicals include phenolic acid, flavonoids, terpenoids, alkaloids, etc. Of these, the terpenoids have activity in the range 0.25–10.5 ppb, which is a much lower concentration than is traditionally recognized for phenolic compounds and alkaloids (Macias, 1993). These chemicals are synthesized in the shikimic acid, acetate, and terpenoid pathways and are differently distributed throughout the rice plants. For instance, ferulic and benzoic acids are found in straw, whereas gallic acid and benzaldehydes are found in leaves (Macias, 1993; Rice, 1985). Many researchers have reported the positive effects of allelopathy as an ecological weed control system by

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selecting rice cultivars with greater allelopathic activity (Ahn and Chung, 2000; Chou, 1995; Chung et al., 1997; Olofsdotter et al., 1995; Tamak et al., 1994; Hassan et al., 1994). Dilday et al. (1994) evaluated the allelopathic effects of about 10,000 accessions from a rice germplasm collection on ducksalad [Heteranthera limosa (Sw.) Willd.], an annual broadleaved weed, in a field study. Chung et al. (2002) reported the allelopathic activity of 23 standard allelochemicals on barnyardgrass, and evaluated the effects on hull extracts from 91 cultivars in the laboratory (Ahn and Chung, 2000). Olofsdotter et al. (1999) examined the weed-suppressing effects of 111 rice cultivars on E. crus-galli both in the laboratory and in the field. Chung et al. (2001) evaluated the allelopathic potential of rice in the laboratory, in a greenhouse, and in the field using extracts and residues, and concluded that genetic variation in allelopathic activity exists among cultivars. These results support previous studies (Dilday et al., 1994; Garrity et al., 1992; Olofsdotter et al., 1995). Also, Chung et al. (2003) evaluated allelopathy potential to E. crus-galli Beauv. var. oryzicola Ohwi with leaves, stems and hulls extracts. Many assessments of the allelopathic potential of rice extracts are available, whereas little information is available on the allelopathic potential of the residues of rice leaves plus stems and hulls. Any basic data derived from this study might indicate a use as an allelopathic component to suppress barnyardgrass through plant breeding. The main purpose of this study was to evaluate the allelopathic activity of barnyardgrass and its effect on seed emergence and seedling growth, in terms of such parameters as height and dry weight, using the leaves plus stems and hulls residues of rice cultivars in a greenhouse.

silica sand in each pot. All pots were steam-sterilized for 5 h before use and were placed on saucers to prevent the loss of water-soluble toxic substances (Chung and Miller, 1995). Plastic plugs were placed in the bottom of each pot to prevent the loss of sand through the holes in the bottom. One hundred surface-sterilized E. crusgalli seeds were planted uniformly 1 cm deep in each pot after two weeks of residue incorporation. Emergence was defined as the coleoptile protrusion through the soil surface and was measured each day for 14 days after planting. After emergence, the seedlings were thinned to 25 plants per pot. Hoagland’s solution I (80 ml; Hoagland and Arnon, 1950) was added every four days to each saucer to maintain adequate moisture. All plants were harvested 14 days after planting. All plants from each pot were measured for shoot length, and the seedlings were dried at 65 C for 4 h to determine dry weight. Control plants were grown in silica sand without residue. The percentage inhibition was calculated using the following equation (Chung et al., 2001): Percentage inhibition ð%Þ   ðcontrol value
residue mixture valueÞ ¼  100 control value 2.2. Statistical analysis The greenhouse experiment was conducted twice with a completely randomized design and three replications. Analysis of variance was performed for all data using a general linear model procedure (SAS Institute, 1988). The pooled mean values were separated on the basis of least significant difference (LSD) at the 0.05 probability level.

3. Results and discussion 2. Materials and methods 3.1. Allelopathic effects of different parts of rice varieties One hundred and fourteen rice cultivars grown at the Konkuk University experimental field in Korea, were harvested and separated in October 2001. The harvested plants (leaves-plus-straw, hulls) were dried at room temperature. E. crus-galli P.Beauv.var.oryzi-cola Ohwi seeds were collected in October 2001. After debris was removed from the seeds by flotation in distilled water, the seeds were stored at
40 C until used in a bioassay. The seeds were surface-sterilized in a 1:10 (v/v) dilution of commercial hypochlorite bleach for 10 min and rinsed several times with distilled water. 2.1. Bioassay in a greenhouse using rice residues This test was conducted in a greenhouse with an average temperature of 26 C. The ground residues 5 g of 114 rice cultivars were mixed thoroughly with 500 g of

The average inhibition on barnyardgrass was higher for Duchungjong (77.7%) than for other varieties. Sixteen varieties showed very high inhibitory effects (>70%). However, three cultivars, including Deokjeokjodo (9.6%), exhibited less than 10% average inhibition (Table 1). When Chung et al. (2003) reported the inhibition exerted by specific rice parts, they examined the inhibitory effects of rice hulls and leaf-plus-straw on barnyardgrass germination rates, and on the percentage and total dry weights. Their results showed that CUBA 65-v-58 caused greatest average inhibition (36.8%) and DOU-U-LAN the least average inhibition (0.5%). The average inhibitory effects of the leaves-plus-straw mixture and hull residue were not significant (Fig. 1). The allelopathic effect was greater on barnyardgrass weight than on other parameters. The inhibitory effect

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Table 1 Inhibitory effect of different parts of rice varieties Varieties

Emergence a

L&S

Height b

Hull

a

L&S

Dry weight b

Hull

a

L&S Top

143(PI 274471) AC 1423 AGUDO ARONGBYEO B1293B-PN-24-2-1 BADOLBYEO BAEKCHALBYEO BAEKGWANGOK BAEKHAEDAL BAEKJICHEONGBYEO BAEKJO BAEKKYEONGJO BAEKMANGJO BAEKNA BAKKYE BANCHONJO BANDALBYEO BARAMDUNGKURI BASMATI BORIBYEO BULDO CHANARAK CHE-SHAU-NAN-BIR CHEONGGUNBYEO CHEONGSANDO CHINDADCHIKI CICA 4 CUBA 65-V-58 DADAJO DAEGOLDO DAEGUDO DAMAGUNG DANGANEUIBANGJU DEOKJEOKJODO DONDUNI KUNLUZ DONG O BYEO DONGSANJO DONNA DORAE DOU-U-LAN (RED STEM) DUCHUNGJONG EUMSEON EUNJO F3-220 GANGCHEONGDO GANGREUNGDO GEUMCHANGDO GEUMJEOMDO GIN SHUN GPNO 12856 GPNO 3005 GUANDO HAMBURERBYEO HEUGBAL HEUGSAEKDO HEUNBE HOCHOKJINDO HONGDODO HUADO HWANGJO

81.8 0 83.1 89.9 35.1 0.0 44.6 60.1 59.5 58.1 35.1 23.6 52.7 39.2 71.6 0.0 6.8 0.0 39.9 50.7 80.4 39.2 60.8 64.9 40.5 70.3 41.2 5.4 75.0 13.5 27.7 95.9 33.8 0.0 22.3 33.8 3.4 20.3 23.0 0 84.5 0.0 0.0 54.1 44.6 79.7 68.9 85.8 40.5 62.2 78.4 70.3 53.4 0.0 19.6 41.9 91.9 81.8 58.1 82.4

74.3 0 16.2 71.6 65.4 50.7 41.9 18.2 38.5 43.9 75.0 17.6 78.4 54.7 62.2 67.6 64.2 0.0 81.1 54.7 10.1 52.0 41.2 79.1 28.4 38.5 87.8 68.2 87.2 6.8 93.2 71.6 43.2 0.0 68.9 83.8 82.4 89.2 31.8 89.9 79.1 19.6 0.0 89.2 59.5 42.6 34.5 52.0 27.7 85.8 30.4 83.8 34.5 29.7 74.3 34.5 53.4 68.9 50.7 58.1

40.6 42.3 42.8 42.1 75.6 50.6 37.1 42.3 50.5 26.0 43.6 49.4 46.8 39.5 33.9 44.1 36.2 50.8 75.7 30.9 31.5 34.0 51.8 37.5 28.0 30.2 42.7 31.8 33.1 42.4 55.1 43.4 44.3 27.7 44.0 43.7 46.6 40.2 44.7 33.4 57.6 13.1 32.3 44.9 39.9 44.8 33.7 38.9 32.6 43.8 59.2 36.7 37.6 39.1 35.7 40.6 33.7 66.4 38.4 30.2

39.6 39.2 34.4 50.1 42.7 51.7 50.1 44.6 31.3 30.9 48.9 42.4 27.1 42.9 39.1 63.7 45.9 17.3 66.6 32.4 36.9 34.7 32.6 38.2 45.8 44.5 54.9 36.2 40.0 24.0 27.0 40.9 36.4 24.3 45.7 25.3 45.9 38.9 48.1 44.9 46.5 45.9 24.6 33.7 38.9 38.0 46.4 44.2 48.9 33.7 42.1 39.1 34.8 19.6 64.7 45.1 53.9 51.2 43.0 52.2

Inhibition (%) 81.7 45.0 89.4 90.3 66.6 49.8 52.6 71.8 90.1 80.7 46.1 57.5 67.3 60.5 83.2 44.1 44.6 49.5 66.7 55.4 82.4 45.3 77.1 67.9 51.7 71.4 68.2 54.5 93.2 38.3 64.9 98.0 52.2 26.6 68.5 61.5 43.1 51.5 55.2 46.3 93.5 10.4 4.7 74.4 63.6 87.1 76.3 90.1 68.1 77.5 85.1 80.7 59.0 29.0 38.8 57.8 89.6 78.6 63.5 79.4

Total b

Hullb Root

Top

85.1 20.4 88.2 92.2 59.2 32.0 30.3 73.6 41.9 59.9 36.1 50.7 68.6 64.6 78.1 25.5 49.7 49.4 41.0 64.8 88.5 64.6 73.8 75.7 53.2 77.7 62.6 34.9 84.1 49.8 56.7 97.1 61.2 41.3 68.4 55.4 37.0 43.4 42.5 45.3 91.0 38.6 30.9 63.6 58.1 86.4 76.6 91.6 56.1 74.4 79.9 79.9 68.2 48.5 57.4 65.8 94.4 85.7 72.7 81.2

79.6 36.7 40.2 80.6 78.1 73.3 63.4 53.6 61.3 62.1 83.8 50.6 83.8 72.0 71.8 84.3 65.0 0.0 90.4 68.3 38.0 61.2 57.7 76.3 52.8 55.0 94.2 80.8 91.3 12.5 95.3 79.3 62.9 0.0 79.0 87.6 88.3 91.4 62.1 93.8 87.3 51.1 0.0 91.0 73.3 57.0 62.7 68.0 64.7 90.0 61.5 90.2 54.6 2.2 87.9 42.0 49.3 73.3 60.6 70.7

Root 82.5 70.7 0 17.6 49.2 55.4 81.9 74.8 70.7 58.1 64.7 46.5 57.3 47.2 39.3 50.4 49.0 52.8 62.0 53.0 83.1 56.5 45.0 42.1 83.7 63.5 73.3 55.9 74.4 64.3 71.8 49.6 27.1 42.4 14.8 19.8 81.5 63.7 71.2 53.6 45.6 51.7 60.5 49.0 55.4 56.3 79.1 64.8 45.4 43.2 39.7 53.4 90.0 67.5 75.8 50.7 90.9 74.3 24.8 26.5 93.0 64.1 82.6 76.1 61.8 49.5 0.0 9.6 52.5 56.3 87.4 59.8 88.3 54.4 90.5 58.2 59.9 45.9 93.1 55.6 82.3 77.7 54.9 27.9 0.0 7.2 89.3 67.5 70.4 56.0 48.5 60.5 51.9 56.4 68.9 67.4 58.7 51.1 90.4 69.1 52.0 58.8 86.8 70.9 53.2 49.4 63.6 28.5 85.5 58.0 48.9 47.1 68.6 66.8 72.3 72.3 58.5 55.7 63.5 64.7 (continued on next page)

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Table 1 (continued) Varieties

Emergence a

L&S

Height b

Hull

a

L&S

Dry weight b

Hull

a

L&S Top

HWANGJU HWANGTODO IR 1044-56 IR 329-9-5-2-2 IR 644-1-63-1-1 IR 781-497-2-3 IRI 233 IRI 268(NONGKWANG) IRI 293(PALGEUM) IRI 301(MANGYUNG) JAERAEJONGNA JANGJO JANGSAMDO JANGWANG JEOKMOSAEK JEONA JEONGDALDO JEONGJO JINHWA KABAEGJO KASARWALA MUNDARA KINGMEN TOUMEN CHIUMU MAMORIAK MON-Z-WUAN MUTANT 12-42 NAMKANGBAEKJO NAMSEON 1 NATO SELECTION NOINDARI NOINDO OEGUKBYEO OLBYEO P 1279 PALMYRA PATBYEO PHILIPPINE 2 PI 389011 OR SD PYEONGBUK 4 PYEONGYANG RED KHOSHA CERMA REXMONT RIKUU 132 SAN CHIAO TSWEN SANCHEONGDO SANGPUNG SANJO SEOGANDODO SEUNGSILJO SHALI I MAHIN SHUANG CHIANG-30-21 SINBAEGSEOG TAICHUNG NATIVE 1 TSAI YUAN CHON WOO-CO-CHIN-YU

0.0 32.4 43.2 83.8 85.1 79.1 57.4 37.8 56.1 41.9 71.6 58.8 66.9 12.8 4.7 0.0 66.9 85.1 28.4 73.6 26.4 60.8 66.9 62.2 66.2 43.9 77.7 87.8 51.4 83.8 69.6 0.0 43.9 81.8 68.2 33.1 40.5 60.8 29.1 53.4 79.7 69.6 43.2 76.4 89.9 68.2 79.1 21.6 58.8 82.4 73.0 48.6 67.6 62.8

56.1 54.1 73.0 59.5 80.4 71.6 89.9 0.0 69.6 61.5 76.4 0.0 31.8 48.0 31.8 54.7 61.5 70.9 68.2 52.7 90.5 60.1 45.3 50.7 87.2 45.3 76.4 77.7 47.3 63.5 62.2 0.0 43.9 60.1 55.4 75.0 67.6 62.8 76.4 33.8 44.6 89.2 75.0 0.0 56.1 18.9 44.6 0.0 71.6 67.6 3.4 62.2 16.2 48.6

35.8 32.2 40.7 39.1 41.7 51.9 48.5 44.6 31.4 40.4 46.7 27.9 37.3 42.3 33.3 34.0 41.3 32.5 31.0 33.2 42.8 45.9 40.3 50.5 38.1 45.4 47.9 45.8 44.5 34.9 2.3 29.8 36.7 38.6 29.9 40.6 43.8 52.8 39.6 44.9 50.0 41.3 46.6 30.9 24.8 26.5 35.0 22.4 42.3 42.4 29.1 35.4 31.3 39.5

60.9 51.7 29.0 42.8 30.0 35.5 38.1 30.6 31.5 42.1 31.2 31.0 40.3 39.8 33.7 45.8 40.4 52.6 36.4 18.9 44.2 44.6 42.1 35.7 42.5 45.7 37.6 36.2 39.3 38.7 48.7 29.0 49.9 35.2 49.7 30.8 40.3 46.4 43.4 44.3 35.8 37.9 34.1 24.8 31.7 40.0 36.9 31.3 33.8 43.2 30.3 36.0 39.9 52.7

Means LSD(0.05)

50.0 55.3

52.9 51.8

39.6 23.9

39.9 18.0

a b

Leaves-plus-straws mixture. Hull residue.

Inhibition (%) 21.1 40.0 70.0 92.6 91.6 89.5 77.9 48.1 73.2 60.4 78.3 54.9 80.9 43.3 15.4 0.0 80.4 86.7 36.7 81.0 61.4 73.8 80.4 76.8 77.5 52.3 88.6 91.0 72.3 88.9 66.6 2.0 65.6 89.4 64.4 70.3 61.8 79.9 40.4 74.4 85.2 80.0 71.2 80.0 95.1 66.4 79.4 39.9 76.8 88.7 78.1 65.9 79.5 76.6 65.6 32.6

Total b

Hullb Root

Top

Root

38.7 54.4 62.5 85.1 88.6 86.9 74.1 53.4 68.0 66.4 81.0 72.9 76.6 53.5 45.3 26.5 83.6 90.5 55.0 74.2 30.0 67.4 76.6 75.2 76.4 62.7 85.4 90.1 65.8 88.6 76.4 24.8 61.6 87.3 79.1 54.9 57.2 76.6 57.2 70.5 82.9 70.1 67.6 84.4 94.0 78.6 84.5 28.4 75.6 86.9 85.1 65.9 80.0 73.1

79.7 58.3 80.5 75.3 84.4 80.0 93.1 23.6 72.4 68.7 77.2 13.3 47.9 60.4 49.5 45.6 66.3 76.9 68.2 66.7 95.6 77.4 67.6 70.9 93.1 67.6 82.8 81.9 66.2 75.3 68.5 0.0 64.2 73.3 67.3 81.7 78.9 73.6 77.6 57.1 66.1 92.8 85.3 16.9 73.6 38.3 57.1 15.7 79.6 82.8 28.9 72.1 48.2 71.3

40.9 45.3 84.9 72.9 88.2 81.0 93.6 48.8 75.4 67.6 85.2 27.3 48.3 62.5 57.2 47.5 57.9 74.4 67.1 68.0 94.3 80.5 69.1 92.5 91.6 64.1 83.2 78.7 60.8 75.7 62.3 0.0 61.0 74.4 59.4 85.1 73.7 69.8 71.1 61.0 70.0 92.7 88.0 21.6 73.9 45.0 58.0 26.7 86.3 84.1 26.1 78.7 48.8 58.4

40.0 46.0 60.4 69.7 73.3 71.7 71.6 35.6 59.7 56.1 68.4 35.1 53.7 45.3 33.9 26.6 62.3 71.2 48.9 58.6 60.9 63.5 61.1 60.7 72.0 53.4 72.4 72.8 55.9 68.7 57.1 0.0 52.9 68.2 59.2 61.3 56.6 65.3 54.3 54.8 62.0 71.9 67.5 41.6 67.4 47.7 59.3 22.0 66.0 72.2 44.2 58.1 51.4 60.4

65.7 39.2

65.2 37.4

64.0 44.2

55.0 23.7

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Fig. 1. Inhibitory effect of rice parts on barnyardgrass.

was lowest on barnyardgrass seedling growth (Fig. 1, Table 1). Leaves-plus-straw mixtures of 18 varieties showed high inhibitory effects on emergence (>80%). In particular, Damagung had an extreme inhibitory effect (95.9%). Sixteen varieties, including Daegudo (93.2%), produced their highest percentage inhibition (>80%) as hull residues (Table 1). These results indicate that the inhibitory effect on weed-seed emergence was induced by rice residues. Thirty-three varieties had extreme inhibitory effects (>80%) on emergence. In this study, the average inhibition by hull residues and leaves-plusstraw were 52.9% and 50%, respectively (Table 1). Two varieties produced the greatest inhibitory effect (>60%) on plant height, exerted by leaves-plus-straw mixtures. The best variety for seedling-growth inhibition was Basmati (75.7%). Four varieties showed high inhibition (>60%) of plant height by hull residues, of which Basmati (66.6%) was the highest. Damagung (95.9%) had the greatest inhibitory effect on emergence. However, it showed only 43.4% inhibition of plant height (Table 1). In the inhibition of aboveground dry weight by leaves-plus-straw mixtures, 32 varieties produced more than 80% inhibition. Furthermore, 29 varieties showed more than 80% inhibition of total dry weight accumulation by leaves-plus-straw. The best variety among these was Damagung (98% and 97.1%, respectively) (Table 1). Twenty-nine varieties showed more than 80% inhibition of aboveground dry weight accumulation by hull residues, of which the effect of Kasarwala mundara (95.6%) was the greatest. Root dry weight accumulation was inhibited by more than 80% by the hull residues of 32 varieties. Of these, Kasarwala mundara (94.3%) showed the greatest inhibition. This result indicates that the hulls of Kasawara mundara best inhibit dry weight accumulation (Table 1).

215

varieties (52.4%). Foreign varieties produced 57.1%, 42%, and 72.5% average inhibition on emergence, height, and dry weight, respectively, whereas domestic varieties had lower inhibitory effects on all counts (47.7%, 38.8%, and 61.6%, respectively) (Fig. 3). In foreign varieties, hull residues showed higher average inhibitory effects (62.7%) than leaves-plus-straw mixtures (59.3%) (Fig. 2). Inhibition of emergence by leaves-plus-straw, of height by hull residues, and of root dry weight by leaves-plus-straw were not significant (Fig. 3, Table 2). Of the foreign varieties, IR 644-1-63-1-1 was the highest (73.3%). However, Duchungjong (77.7%) had the highest inhibitory effect of the domestic varieties and of all varieties (Table 1). The results of this study are not in total agreement with the report of Ahn and Chung (2000), perhaps owing to differences in materials and methods. 3.2.2. Inhibitory effect in terms of maturation time Varieties with intermediate maturation times exerted higher percentages of inhibition (59.3%) than varieties maturing at other rates (early 50.2% and late 56.1%). However, the difference between the intermediate- and late-maturing groups was not significant (Table 3). The average inhibition by leaves-plus-straw mixtures of early, intermediate-, and late-maturing groups were

Fig. 2. Comparison of total inhibitions by leaves-plus-straw mixtures and hull residues of different origins.

3.2. Evaluation of rice genetic and phenotypic characters on allelopathic effects 3.2.1. Inhibitory effect by origin In terms of origin, foreign varieties of rice showed higher percentages of inhibition (61%) than domestic

Fig. 3. Comparison of percentage inhibition between domestic and foreign varieties.

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Table 2 Inhibitory effect of rice varieties of different origins on barnyardgrass Emergence Origin Group

a

Height b

L&S

a

Hull

Dry weight b

L&S

L&Sa

Hull

Hullb

Top Root Top Root Domesticc 47.3 52.7 Foreignd LSD (0.05) 10.1

48.0 61.4 9.4

38.0 43.3 3.6

Inhibition 39.6 40.7 3.2

(%) 61.9 64.9 73.9 67.3 6.9 6.7

59.7 59.9 76.1 72.7 7.8 7.7

a

Leaves-plus-straw mixture. Hull residue. c Domestic varieties. d Foreign varieties. b

Fig. 4. Comparison of total inhibitions by leaves-plus-straw mixtures and hull residues in varieties with different maturation times.

Table 3 Inhibitory effects of maturation rate of rice varieties on barnyardgrass Emergence Maturity Group

a

L&S

Height b

Hull

a

L&S

Dry weight b

Hull

L&Sa

Hullb

Top Root Top Root Earlyc Intermediated Latee LSD (0.05)

37.2 58.3 52.8 11.0

49.3 53.2 53.7 10.8

Inhibition 39.5 39.0 41.7 41.3 37.7 39.2 4.1 3.6

(%) 54.7 60.9 74.1 69.7 69.0 67.0 7.5 7.5

60.6 60.3 68.9 67.0 64.9 64.6 9.0 8.8

a

Leaves-plus-straw mixture. Hull residue. c Early-maturing. d Intermediate-maturing. e Late-maturing. b

48.1%, 61%, and 56.6%, respectively. Average percentages of inhibition by the hull residues of early, intermediate-, and late-maturing groups were 52.3%, 57.7%, and 55.6%, respectively (Fig. 4). Average inhibition of emergence, height, and dry weight by the intermediate-maturing group were 55.8%, 41.5%, and 69.9%, respectively (the corresponding early group values were 43.3%, 39.3%, and 59.1%, respectively; the late group values were 53.3%, 38.5%, and 66.4%, respectively) (Fig. 5). The greatest inhibition was exerted by Dadajo (74.3%) in the early maturing group; by Duchungjong (77.3%) in the intermediate-maturing group; and by Mutant 12–42 (72%) in the late-maturing group (Table 1). 3.2.3. Effect of hull colour on inhibitory effect Coloured hulls showed 55.9% inhibition, whereas colourless hulls showed 65.4% inhibition. The leavesplus-straw mixtures and hulls of varieties with coloured hulls had greater average inhibitory effects (55% and 56.2%, respectively) than varieties with colourless hulls

Fig. 5. Comparison of percentage inhibition in varieties with different maturation times.

Fig. 6. Comparison of total inhibitions by leaves-plus-straw mixtures and hull residues in varieties with coloured or colourless hulls.

(54.5% and 49.9%, respectively) (Fig. 6). Varieties with coloured hulls showed more inhibition of root dry weight by hull residues (65.4%) than varieties with colourless hulls (55.9%). The coloured-hull group also showed more inhibitory effect on emergence and height than the colourless-hull group. However, these differences were not significant (Fig. 7, Table 4). Arongbyeo was the most inhibitory of the colourless-hull group

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Fig. 7. Comparison of percentage inhibition by coloured and colourless hulls.

Table 4 Inhibitory effect of hull colour of rice varieties on barnyardgrass

Hull Group

Emergence

Height

L&Sa

L&Sa Hullb L&Sa

Hullb

Dry weight Hullb

Top Root Top Root Colourless hull 45.0 Coloured hull 49.7 LSD (0.05) 12.2 a b

47.8 52.9 11.5

Inhibition (%) 40.4 37.1 65.9 66.6 39.4 40.5 65.4 65.4 4.4 3.8 8.5 8.1

217

effect of the leaves-plus-straw mixture of the colouredawn group was 56.8%, whereas the values for the colourless-awn and awnless groups were 54.6% and 55.4%, respectively. On the other hand, the hull residues of the awnless, colourless-awn, and coloured-awn group produced inhibitory effects of 56.5%, 54.4%, and 53.7%, respectively (Fig. 8). The leaves-plus-straw mixture of the coloured-awn group showed the highest percentage inhibition among the three groups (50.3% on emergence; 40.8% on height; 68.1% on dry weight). The hull residue of the awnless group showed the highest percentage inhibition (53.5% on emergence; 40.1% on height; 67.1% on aboveground dry weight; 65.3% on root dry weight) (Table 5). In the colourless- and coloured-awn groups, Damagung (76.1%) and IR 6441-63-1-1 (73.3%) had the highest percentages of inhibition, respectively. These results indicate that inhibition is not affected by the occurrence of colour on the awn (Fig. 9). No reports have correlated allelopathic effect with the genotypic or phenotypic characters of rice varieties until recently. The objective of this study was to screen rice cultivars for allelopathic potential using leaves-plus-stem and hull

58.9 55.9 65.8 65.4 9.7 9.4

Leaves-plus-straw mixture. Hull residue.

Table 5 Inhibitory effect of awn of rice varieties on barnyardgrass Emergence Awn Group

a

L&S

Height b

Hull

a

L&S

Dry weight b

Hull

L&Sa

Hullb

Top Root Top Root Awnless Colourless Awn Coloured LDS (0.05) a b

47.8 49.3

53.5 50.6

Inhibition (%) 40.2 40.1 64.6 65.9 38.6 40.0 65.1 64.4

67.1 65.3 63.2 63.7

50.3 12.2

52.2 11.5

40.8 4.4

62.9 60.5 9.7 9.5

39.2 3.9

68.1 68.1 8.5 8.1

Fig. 8. Comparison of total inhibitions by leaves-plus-straw mixtures and hull residues in varieties with and without coloured or colourless awns.

Leaves-plus-straw mixture. Hull residue.

(74.8%). This result indicates that coloured hulls only affect the inhibition of root dry weight. 3.2.4. Effect of the presence and colour of awns on inhibitory effect Awnless, colorless-awn, and coloured-awn groups did not differ significantly in average inhibition (55.6%, 55%, and 53.5%, respectively) (Table 5). The inhibitory

Fig. 9. Comparison of percentage inhibition in varieties with and without coloured awns and awnless.

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residues mixture in order to provide a new selection method for development of allelopathic cultivars. This study demonstrates that inhibitory substances in rice cultivars should be extracted by irrigation water which may offer a practical system against barnyardgrass in the field. One limitation of this study is that the concentration of allelopathic substances in residue mixture may be greater than in fresh material and subject to positive or negative effects from soil components. The duration of allelopathic substances contained in the residue or released by decomposition, which were not evaluated may be shorter than in the field. Further investigations are needed to investigate potential allelopathic cultivars under field conditions.

Acknowledgements The authors wish to acknowledge in the financial support of the Rural Development Administration made in the Biogreen 21 project year of 2003. This work was partially supported to W.S. Jung by the faculty research fund of Konkuk University in 2002.

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