Echinochloa Oryzicola Research Articles

Antioxidative responses and their relation to salt tolerance in Echinochloa oryzicola Vasing and Setaria virdis (L.) Beauv.

Two gramineous species among wild plants, Echinochloa oryzicola Vasing and Setaria viridis (L.) Beauv., and Oryza sativa L. cv. Nipponbare were subjected to salt stress. The relative growth rate (RGR), Na content, photosynthetic rate, antioxidant enzymes activity (superoxide disumutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR)), and malondialdehyde (MDA) content in leaves after NaCl treatment were studied. RGR significantly decreased in O. sativa more than in E. oryzicola and S. viridis. Comparatively salt-tolerant S. viridis showed higher growth rate, lower Na accumulation rate in leaves, higher photosynthetic rate, and induced more SOD, CAT, APx, and GR activity and lower increase of MDA content as compared to the salt-sensitive O. sativa. At the same time, the comparatively salt-tolerant E. oryzicola also showed higher growth rate, much lower Na accumulation and no observable increase of MDA content, even though the CAT and APx activities were not induced by salinity. These results suggested that the scavenging system induced by H2O2-mediated oxidative damage might, at least in part, play an important role in the mechanism of salt tolerance against cell toxicity of NaCl in some gramineous plants

Oxidative injury induced by the herbicide quinclorac on Echinochloa oryzicola Vasing. and the involvement of antioxidative ability in its highly selective action in grass species

To investigate the possible involvement of antioxidative ability in the highly selective action of the herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) in grass species, quinclorac-induced oxidative injuries and the activities of the antioxidative enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbic acid peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) were studied in tolerant rice ( Oryza sativa L. cv. Nipponbare) and a particularly susceptible grass weed, Echinochloa oryzicola Vasing. There were no significant differences in total chlorophyll content, formation of thiobarbituric acid-reactive substances (TBARS), and ethane and ethylene productions between 1 μM quinclorac-treated and control seedlings of rice both under continuous light and dark conditions. In contrast, the chlorophyll content in leaves decreased, and TBARS formation in shoots and ethane evolution increased in quinclorac-treated E. oryzicola seedlings under continuous light for 24 h. These changes were not observed in the dark, indicating that light enhanced the selective activity of quinclorac between rice and E. oryzicola. α-Tocopherol (α-TOH), a free radical scavenger, significantly suppressed quinclorac-induced TBARS formation in shoots and chlorophyll loss in the leaves of E. oryzicola. Antioxidant enzyme assays showed that the constitutive activities of SOD, CAT, APX, and GR enzymes in the shoots of E. oryzicola were lower than those in rice. Furthermore, there were significant correlations between the constitutive activities of APX and GR in shoots and chlorophyll content (% of control) in leaves after rice, corn ( Zea mays L. cv. Honey Bantam), E. oryzicola, E. crus-galli Beauv. var. crus-galli, and E. crus-galli var. formosensis Ohwi were treated with quinclorac. These results suggest that the difference in hereditary antioxidative ability is one factor that results in the particularly high selectivity of quinclorac between rice and E. oryzicola.

Synthesis and herbicidal activity of new oxazinone herbicides with a long-lasting herbicidal activity against Echinochloa oryzicola.

Chemical modification of the herbicide 1-[2-(benzothiazol-2-yl)isopropyl]-4-methyl-3-phenyl-5H-pyrrolin-2-one (MI-2826) has revealed a new oxazinone herbicide, 3-[2-(7-chlorobenzothiazol-2-yl)isopropyl]-2,3-dihydro-6-methyl-5-phenyl-4H-1,3-oxazin-4-one (MI-3069), for use in paddy fields. In comparing the phyototoxicity of the two herbicides to transplanted rice, the latter was superior to the former and kept the same predominant characteristic to control Echinochloa oryzicola Vasin for a long period of time owing to its long-lasting residual effect.

Effect of naringenin on the growth and lignin biosynthesis of gramineous plants

Lignin biosynthesis is essential for plant growth. 4‐Coumarate CoA ligase (4‐CL, EC6.2.1.12) is involved in the monolignol synthesis and occupies a key role in regulating carbon flow into the phenylpropanoid metabolism pathway. Naringenin, one of the metabolites in this pathway, is known as a potent in vitro inhibitor of 4‐CL. The growth of rice (Oryza sativa L. cv. Koshihikari), maize (Zea mays L. cv. Yellow corn) and Echinochloa oryzicola Vasing seedlings at the 2nd leaf stage was inhibited after continuous root application with 0.1 mmol L−1 naringenin for 1 week, although naringenin did not kill these gramineous plants. The highest inhibition of fresh weight increase was observed in maize, followed by rice and E. oryzicola. The symptoms in these plants were root browning, delay of leaf/root development and shoot dwarfing. Naringenin treatment increased the contents of 4‐CL substrates, cinnamic acid, 4‐coumaric acid, caffeic acid and ferulic acid from 1.2 to 7.2 times and from 1.2 to 3.5 times in shoots and roots, respectively, except for ferulic acid in E. oryzicola roots. It also caused a slight decrease of the lignin content and alteration of lignin constitutions in rice plants. These results suggested that the monolignol pathways after 4‐CL towards lignin has the possibility to be the novel action sites of plant growth retardants, although further investigations are needed to clarify the mode of action.

Synthesis and Herbicidal Activity of Novel 3-Alkoxycarbonyl-3-aryl-2, 3-dihydro-2-oxo-1H-pyrrole Derivatives

In the course of efforts to find novel compounds with improved crop safety in transplanted rice by the modification of 1-[1-(3,5-dichlorophenyl)-1-methylethyl]-4-methyl-3-phenyl-3-pyrrolin-2-one (1a), which was reported to have excellent herbicidal activity against paddy weeds, 2,3-dihydro-2-oxo-1H-pyrrole derivatives with a quaternary carbon atom having an alkoxycarbonyl group at the α-position of the cyclic amide were synthesized and examined. Among these compounds, methyl 1-[1-(3,5-dichlorophenyl)-1-methylethyl]-2,3-dihydro-4-methyl-2-oxo-3-phenyl-1H-pyrrole-3-carboxylate (2a) was not only active against Echinochloa oryzicola and Scirpus juncoides but also compatible with transplanted rice even in harsh conditions. On the basis of preliminary experimental results, it was thought that 2a would generate the corresponding 2-oxo-3-pyrrolin (1a) through the metabolic degradation of the methoxycarbonyl moiety. © Pesticide Science Society of Japan

積雪寒冷地におけるタイヌビエの許容残草量と土中種子数推移の予測に基づく要防除水準

積雪寒冷地におけるタイヌビエの許容残草量と土中種子数推移の予測に基づく要防除水準

Alfalfa, rice by‐products and their incorporation for weed control in rice

Two alfalfa varieties, namely Rasen and Yuba, and rice by‐products of Koshihikari (Oryza sativa L. cv. Japonica), including hull and bran were used for weed control in rice. Rasen and Yuba were sequentially evaluated to have the strongest allelopathic potential among eight common alfalfa varieties in Japan. Rasen, Yuba and rice by‐products in a laboratory experiment exhibited suppression of emergence of lettuce (Lactuca sativa L.), barnyardgrass (Echinochloa oryzicola Vasing.), and monochoria (Monochoria vaginalis Presl var. plantaginea Solms‐Laub.). In a paddy field experiment, at 15 days after application, a dose of 1 ton ha−1 of alfalfa, rice by‐products and the incorporated alfalfa‐rice by‐products significantly inhibited weed growth and reduced weed species, except for rice bran. However, at 40 days after application, the greatest weed control was sequentially recorded with Yuba (95.2%), Rasen (90.5%) and the incorporated Rasen‐hull (88.3%). Rice hull exhibited stronger (51.7%) weed control than the negligible weed control of rice bran (25.1%). Inhibition of both Rasen and Yuba on weed emergence after application became more vigorous, whereas those of rice by‐products were gradually devitalized. Rasen had a maximum increase of rice yield (80.6%) compared to the control and it was slightly higher (9.6%) than the herbicide treatment. Findings showed that Rasen was the most promising material for weed control among those studied. Results denoted that weed control capability of allelopathic materials had an impetuous effect on rice growth and yield.

Synthesis and Herbicidal Activity of 4-Thiazolone Derivatives and Their Effect on Plant Secretory Pathway

In the course of study to develop new herbicidal compounds, we found that some 4-thiazolone derivatives possessed herbicidal activity against several paddy weeds. As a result of a structure-activity relation study, 5-(2-chloroethyl)-5-methyl-2-(3-methyl-2,3-dihydro-1,4-benzoxazin-4-yl)-4-thiazolone (CMT) was selected as one of the potential herbicides for rice. CMT showed potent herbicidal activity against paddy weeds, especially barnyardgrass (Echinochloa oryzicola) and three-square grass (Scirpus juncoides). The herbicidal activity of CMT appeared to be caused by specific inhibition in the growing tissues. Electron microscopic observations of CMT-treated barnyardgrass revealed that exposure to 10 μM CMT for 4 hr caused swelling of the endoplasmic reticulum (ER) and Golgi apparatus, the separation of plasma membranes from cell walls, and an accumulation of small vesicles in the plasma membrane-cell wall interspace. These findings suggest that CMT acts primarily as an inhibitor of the secretory pathway, resulting in a dysfunction of cell wall biosynthesis.

積雪寒冷地水田におけるタイヌビエの土中種子数の推移

積雪寒冷地水田におけるタイヌビエの土中種子数の推移

積雪寒冷地水田におけるタイヌビエの種子生産量と土中種子数の増減予測モデル

積雪寒冷地水田におけるタイヌビエの種子生産量と土中種子数の増減予測モデル

Molecular identification of Echinochloa oryzicola Vasing. and E. crus‐galli (L.) Beauv. using a polymerase chain reaction–restriction fragment length polymorphism technique

Polymerase chain reaction (PCR) and polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) techniques were applied for establishing the reliable practice in identification of Echinochloa oryzicola Vasing. and E. crus‐galli (L.) Beauv. (barnyardgrass). Total DNA was extracted from 18 accessions and 86 individuals of E. oryzicola, 33 accessions and 140 individuals of E. crus‐galli var. crus‐galli, 23 individuals of E. crus‐galli var. praticola, and six individuals of E. crus‐galli var. formosensis that were collected from Japan. A partial region of intergenetic spacer between trnT and trnL, and an intron of trnL were amplified separately using a trn‐a and trn‐b1 primer set, and a trn‐c and trn‐d primer set, respectively. All individuals of E. oryzicola showed the same fragment amplified by the trn‐a and trn‐b1 primer set. The fragment was 481 bp in length, and was undigested by EcoR I, whereas all individuals of E. crus‐galli, including three botanical varieties, showed the same fragment with a 449‐bp length. The fragment was digested by EcoR I into two fragments (178 and 271 bp). The fragment amplified by the trn‐c and trn‐d primer set in all individuals of E. oryzicola was digested by Alu I into two fragments (174 and 452 bp), but undigested by Dra I. In contrast, the fragment amplified by the trn‐c and trn‐d primer set in all individuals of E. crus‐galli was digested by Dra I into two fragments (134 and 487 bp), but undigested by Alu I. There was no intraspecific variation in these regions; thus, these two species are easily identifiable by using our method.

Herbicide pyrazolate causes cessation of carotenoids synthesis in early watergrass by inhibiting 4‐hydroxyphenylpyruvate dioxygenase

In aqueous solution, the herbicide pyrazolate [4‐(2,4‐dichlorobenzoyl)‐1,3‐dimethyl‐5‐pyrazolyl p‐toluenesulfonate] is rapidly hydrolyzed to destosyl pyrazolate (DTP), 4‐(2,4‐dichlorobenzoyl)‐1,3‐dimethyl‐5‐hydroxypyrazole, which is an active form of the herbicide. The objective of this study was to examine the effect of pyrazolate and DTP on carotenoids synthesis in susceptible weed, early watergrass (Echinochloa oryzicola Vasing.). Furthermore, their in vitro effect on 4‐hydroxyphenylpyruvate dioxygenase (HPPD) was determined. Roots of the plants at the two‐leaf stage were soaked for 24 h into pyrazolate (5 × 10–5 mol L−1) or norflurazon (10–6 mol L−1) solution containing 0.5% volume of acetone. At the first sampling time (3 days after treatment: 3 DAT), the chlorophyll content in the third leaves of pyrazolate‐treated plants were not different compared with the untreated control, but it was decreased between 3 and 6 DAT. The declining pattern of β‐carotene in the third leaf of early watergrass was very similar to that of chlorophyll. Both herbicides induced greater accumulation of phytoene in the third leaves of early watergrass 3 DAT, and the levels were kept until 9 DAT. However, feeding of homogentisate reduced the phytoene accumulation only in pyrazolate‐treated plants, suggesting the site of action of the herbicide located in the pathway of plastoquinone synthesis. In a HPPD assay, DTP revealed to inhibit the enzyme with an IC50 value of 13 nmol L−1 and that of pyrazolate was 52 nmol L−1. In the pyrazolate solution used in the assay, some of the herbicide possibly has been hydrolyzed to DTP. From the all results obtained, it is strongly suggested that pyrazolate inhibits carotenoids synthesis and causes bleaching on the developing leaves by the similar mechanism with norflurazon, but its action site is not phytoene desaturase and is HPPD.

Inhibition of very-long-chain fatty acid formation by indanofan, 2-[2-(3-chlorophenyl)oxiran-2-ylmethyl]-2-ethylindan-1,3-dione, and its relatives.

Indanofan and its analogs inhibited the elongation of stearoyl- or arachidoyl-CoA by [2-14C]-malonyl-CoA in leek microsomes from Allium porrum. Although the precise mode of interaction of indanofan at the molecular level is not completely clarified by the present study, it is concluded that indanofan and analogs act as inhibitor of the elongase enzyme involved in de novo biosynthesis of fatty acids with an alkyl chain longer than C18, called very-long-chain fatty acids (VLCFAs). For a strong inhibition of VLCFA formation chloro substituents at the benzene ring and the oxirane group were necessary. Furthermore, the greenhouse test showed strong activity for indanofan and its analogs, and the scores coincided with cell-free elongation inhibition. The cell-free assay, however, failed to indicate any activity for an analog having a methylene instead of the oxirane group, while both Digitaria ciliaris and Echinochloa oryzicola were killed with 1 kg a.i./ha. This finding cannot be discussed because the applied use rate of 1 kg a.i./ha is too high to allow for a score differentiation. For high concentrations of this compound additional unknown inhibitory effects may be involved besides fatty acid elongation.

Competitiveness of Four Rice Cultivars against Barnyardgrass, Echinochloa oryzicola Vasing, with Reference to Root and Shoot Competition

Four cultivars of rice (Oryza sativa L.) different in plant stature were grown on a paddy field, fairly fertile without nitrogen application, with or without barnyard grass, Echinochloa oryzicola Vasing, in the middle of the rice rows. The reduction of the growth variables of the four cultivars by competition with E. oryzicola was examined. The effect of a veneer board inserted in the soil between the rice and barnyardgrass rows was also examined to evaluate the growth reduction by shoot competition (WCS) and root competition (WCr) separately. On the average, the reduction of top dry weight (DWtop) by competition with weed (full competition, WCf) and by WCr increased with the time during the early growth period. Thereafter, the reduction of DWtop by WCr decreased steeply and instead the reduction by WCS increased and became a primary factor of the reduction by WCf in the late growth period. Nitrogen accumulation in the top (Ntop) tended to be reduced at a higher rate than DWtop by WCr. The cultivar difference in the rate of DWt0P reduction by WCf was largest at maturity ranging from 0.22 in Ch86 (very tall indica) to 0.45 in Taichung65d47 (short japonica), and was intermediate in Taichung65 (moderately tall japonica) and Takanari (moderately short indica). The reduction of DWtop and Ntop by WCS in all cultivars almost fully accounted for that by WCf at maturity and closely correlated with the height of rice plant. Although the rate of DWt0P reduction by WCr before heading significantly differed among cultivars (0.13 - 0.28), it did not contribute to the rate of DWtop reduction by WCf at maturity (0.01 - 0.06). These results indicated that shoot competition was a more important factor to cause cultivar difference in the reduction of final biomass by competition with E. oryzicola. Considering its great contribution to WCf during the early growth period especially for Ntop, WCr might be an important factor in the competition with weed of rice cultivars under crucially nitrogen-limited conditions.

Effects of acid extracts of tomato (Lycopersicon esculentum Mill.) and carrot (Daucus carota L.)wastes from the food industry on the growth of some crops and weeds

The effects of acid extracts of tomato (Lycopersicon esculentum Mill.) and carrot (Daucus carota L.) juice wastes from the food industry on the growth of five species of crops and four weeds were examined. The acid extract of the tomato juice waste promoted the shoot and root growth of tomato, Chinese cabbage, corn, and radish, but not the growth of oat seedlings. The extract did not promote the shoot growth of weeds tested, and it inhibited the root growth of the weeds that included barnyardgrass (Echinochloa oryzicola Ohwi), southern crabgrass (Digitaria ciliaris Koel.) and Japanese barnyard millet (Echinochloa utilis Ohwi). The carrot juice waste was also examined as another waste from the food industry. The effect of the acid extract of carrot juice waste showed significant promoting effects on the root growth of Chinese cabbage; however, the effects on other plants were lower than that of tomato juice waste. It also did not inhibit the growth of weeds. These results suggested that the acid extract from tomato juice waste is useful as plant-growth substances because they have a promoting effect on the shoot and root growth of crops, and an inhibitory effect on the root growth of some weeds.

Weed control with alfalfa pellets in transplanting rice

Alfalfa [Medicago sativa L. (M. media, M. falcate)] plants contain allelochemicals that have detrimental effects on their own growth and that of surrounding plants. Alfalfa pellets, used as a food for livestock, were used as the material for the control of weeds in this study. In a greenhouse experiment, alfalfa pellets applied at 1–3 tons ha−1 completely inhibited the emergence of abunome (Doparium junceum Hamilt.), false pimpernel (Lindernia pyxidaria L.), and long stemmed water wort (Elatine trianda Schk. var. pedicellata Krylov) The number and the dry weight of emerged Echinochloa oryzicola plants were significantly reduced. Application of 3 tons ha−1 alfalfa pellets completely inhibited the emergences of Eleocharis acicularis and Rotala indica. Results demonstrated that the inhibitory effect of alfalfa pellets became greater as the dose increased, and it also varied among weed species. Furthermore, the paddy field experiment suggested that the dose of 1–2 tons ha−1 of alfalfa pellets could control more weed species without any rice plant injury.

Inhibition of Very-Long-Chain Fatty Acid Biosynthesis by 2-Chloro-N-(3-methoxy-2-thenyl)-2′,6′-dimethylacetanilide, Thenylchlor, and Its Analogs

Abstract The herbicide thenylchlor and its analogs inhibited the incorporation of [1- 14 C]oleate and [2- 14 C]malonate into very-long-chain fatty acids (VLCFAs) in Scenedesmus cells and leek microsomes from Allium porrum , respectively. Although the precise mode of interaction of thenylchlor at the molecular level is not completely clarified by the present study, it is concluded that thenylchlor acts as an inhibitor of the elongase enzyme involved in biosynthesis of fatty acids with alkyl chains longer than C 18 . For a strong inhibition of VLCFA formation, an N,N-disubstituted amide moiety of chloroacetamides is required. Furthermore, 2,6-dimethyl substituents at the benzene ring and electron-donating groups such as methoxyl or methyl at the 3 position of the thiophene ring produce a strong inhibition of VLCFA formation. A correlation was found between the phytotoxic effect against barnyardgrass ( Echinochloa oryzicola ) and the decreased VLCFA formation.

Very-long-chain fatty acid biosynthesis is inhibited by cafenstrole, N,N-diethyl-3-mesitylsulfonyl-1H-1,2,4-triazole-1-carboxamide and its analogs.

The rice herbicide cafenstrole and its analogs inhibited the incorporation of [1-(14)C]-oleate and (2-(14)C]-malonate into very-long-chain fatty acids (VLCFAs), using Scenedesmus cells and leek microsomes from Allium porrum. Although the precise mode of interaction of cafenstrole at the molecular level is not completely clarified by the present study, it is concluded that cafenstrole acts as a specific inhibitor of the microsomal elongase enzyme involved in the biosynthesis of fatty acids with alkyl chains longer than C18. For a strong VLCFA biosynthesis inhibition an -SO2- linkage of the 1,2,4-triazole-1-carboxamides was required. Furthermore, N,N-dialkyl substitution of the carbamoyl nitrogen and electron-donating groups such as methyl at the benzene ring of 1,2,4-triazole-1-carboxamides produced a strong inhibition of VLCFA formation. A correlation was found between the phytotoxic effect against barnyardgrass (Echinochloa oryzicola) and impaired VLCFA formation.

Differential glutathione S-transferase isozyme activities in rice and early watergrass seedlings

Glutathione S-transferase (GST) isozymes were investigated in one-leaf-stage rice (Oryza sativa L. cv. Nipponbare) and early watergrass (Echinochloa oryzicola Vasing) shoots after being induced by treatment with a combination of pretilachlor [2-chloro-2′,6′-diethyl-N-(2-propoxyethyl)acetanilide] and fenclorim (4,6-dichloro-2-phenylpyrimidine) using DEAE-Sephacel anion exchange chromatography. Non-treated plants contained GST isozymes that had activity to the following substrates: three isozymes for l-chloro-2,4-dinitrobenzene (CDNB), six isozymes for pretilachlor and three isozymes for fenclorim in rice shoots; and four isozymes for CDNB, three or four isozymes for pretilachlor and two or three isozymes for fenclorim in early watergrass shoots. Glutathione S-transferase isozyme activities of non-treated plants were higher in rice than in early watergrass, especially in the case of GST activity with fenclorim as a substrate. Pretreatment of rice roots with a combination of pretilachlor and fenclorim increased the activity of the constitutively expressed isozymes that exhibited activity with CDNB, pretilachlor and fenclorim. This pretreatment also caused the appearance of one new GST(fenclorim) isozyme. Pretreatment of early watergrass roots with a combination of pretilachlor and fenclorim produced almost no increase in activity of some constitutively expressed isozymes that exhibited activity to CDNB and fenclorim, although it partly increased the peaks to corresponding to pretilachlor. The induction of GST was higher in rice than that in early watergrass. These results indicated that the isozyme pattern and substrate specificity of GST isozymes in rice were different from those in early watergrass. Furthermore, the selectivity of pretilachlor between rice and early watergrass may be related to different constitutively expressed GST(pretilachlor) isozyme activities and the induction of GST(pretilachlor) isozyme activities in the combination treatment.

Strategy of Echinochloa oryzicola Vasing. for survival in flooded rice

Echinochloa oryzicola Vasing. (= Echinochloa phyllopogon Stapf ex Kessenko) is an obligate weed with an elaborated survival strategy in the flooded rice of Japan. In this review various adaptive characters of the weed, which comprise the survival strategy, are discussed through the life cycle. The weed is distributed only in flooded rice. Seeds (spikelets) buried in the soil exhibit annual cycles between dormant and non‐dormant state, and non‐dormant seeds recurrently appear in spring when rice growers start to prepare seedling beds and fields for rice transplanting. The non‐dormant seeds have unique characters metabolically adapted to submerged conditions to germinate and grow by the anaerobic respiration through alcohol fermentation. The weed has seemingly perfect mimicry of the rice plants throughout its development from seedling to heading, by which the weed escapes from manual weeding. In a rice paddy, the weed starts heading coincidentally with the rice plants at the period when the growers are reluctant to walk in the rice paddy to weed. Irrespective of plant height of the rice cultivar, the weed develops a few upper leaves above the rice canopy during the heading period of rice. This phenotypic plasticity of E. oryzicola in plant height is one of the characters conferring its competitive aggressiveness in flooded rice. When weeding is begun again after heading, the dormant weed seeds escape weeding by shattering and join the soil seedbank. The dormant seeds express the gene of an enzyme catalyzing ATP synthesis through the mitochondrial oxidative phosphorylation more abundantly, and have larger oxygen absorption and enzyme activity of the aerobic respiration than the non‐dormant seeds, suggesting that the dormant seeds maintain viability by the conventional aerobic respiration in the paddy soil drained from rice harvesting in fall to the next early spring. The various adaptive characters comprising the survival strategy of E. oryzicola in flooded rice consist of those inherited from the wild progenitor and those selected by the crop cultivation pressure. It is suggested that both the mimicry of the weed and the heading coincident with the rice plants have been acquired by the large selection pressure of frequent weeding, which has been done over the past hundred years. However, today, the manual weeding is substituted with herbicides, which cannot detect the mimicry and heading photoperiodic sensitivity. As a result, the dominant species of Echinochloa weeds in flooded rice is changing from E. oryzicola to Echinochloa crus‐galli var. crus‐galli that has neither mimicry nor photoperiodic sensitivity synchronizing to that of rice, but is more competitive against rice.