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Echinochloa crus-galli is a major weed in rice fields in China, and quinclorac has been long used for its control. Over-reliance of quinclorac has resulted in quinclorac resistance in E. crus-galli. Two resistant (R) E. crus-galli populations from Hunan, China were confirmed to be at least 78-fold more resistant to quinclorac than the susceptible (S) population. No difference in foliar uptake of 14C-labelled quinclorac was detected between the R and S plants. However, a higher level of 14C translocation and a lower level of quinclorac metabolism were found in the R plants. Basal and induced expression levels of β-cyanoalanine synthase (β-CAS) gene and β-CAS activity were not significantly different between the R and S plants. However, the induction expression of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1) gene by quinclorac treatment was evident in the S plants but not in the R plants. Quinclorac resistance in the two resistant E. crus-galli populations was not likely to be related to foliar uptake, translocation or metabolism of quinclorac, nor to cyanide detoxification via β-CAS. Thus, target-site based quinclorac signal reception and transduction and regulation of the ethylene synthesis pathway should be the focus for further research. Keywords: Echinochloa crus-galli, Quinclorac resistance, Quinclorac metabolism, β-cyanoalanine synthase, 1-aminocyclopropane-1-carboxylic acid synthase, 1-aminocyclopropane-1-carboxylic acid oxidase, Rice

Alternative irrigation systems are viable options to reduce water footprint in rice; however, it could increase the difficulty of controlling weeds, as the water layer prevent weed emergence. Despite the environmental importance, there is no knowledge regarding effective chemical control of Echinochloa crus-galli (L.) P. Beauv. under contrasting field layouts and irrigation systems in dry-seeded rice. In this study, we quantified the efficacy of some pre-emergence (PRE) and post-emergence (POST) herbicide sequences and tank mixtures to control E. crus-galli under continuous and intermittent irrigation at two different field layouts. The experiment was conducted during three growing seasons between 2012 and 2014, in two edaphoclimatic regions of Uruguay. The rice yield was directly related to the efficacy of controlling of E. crus-galli at flowering (R2 ≈ 0.60). The efficacy of chemical options to control E. crus-galli was not affected by the irrigation or the field layout system. Clomazone PRE followed by penoxsulam was the most effective option (80% weed control). The results suggest that chemical options are available to control E. crus-galli when applying alternative field layout and irrigation systems that promote improved water efficacy in rice. We expect this new approach to control E. crus-galli be useful in reducing water needs, and hence making rice production more sustainable.

Dose-response experiments were conducted to assess the sensitivity of one susceptible and three putative resistant (R1, R2, and R3) barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] biotypes to florpyrauxifen-benzyl and cyhalofop-butyl alone and as a formulated premix. Subsequently, potential resistance mechanisms of the barnyardgrass were evaluated. Based on biomass reduction results, resistant/susceptible ratios were calculated for R1 (7.0–50), R2 (7.0–150), and R3 (18–214) biotypes. Absorption and translocation of [14C]-florpyrauxifen-benzyl decreased in R1 and R3 biotypes, but not for [14C]-cyhalofop-butyl. The metabolism of [14C]-florpyrauxifen-benzyl to [14C]-florpyrauxifen-acid was >2-fold less in resistant biotypes (9–11%) than in the susceptible biotype (23%). Moreover, the production of [14C]-florpyrauxifen-acid in susceptible barnyardgrass (not in the R biotypes) increased 3-fold when florpyrauxifen-benzyl and cyhalofop-butyl were applied in mixture compared to florpyrauxifen-benzyl applied alone. The tested barnyardgrass biotypes had no mutation in the Transport Inhibitor Response1, auxin-signaling F-box, and acetyl coenzyme A carboxylase genes. Although further studies on cyhalofop-butyl resistance with respect to analysis of specific metabolites are needed, our findings in this study demonstrates that the evolution of florpyrauxifen-benzyl resistance in multiple resistant barnyardgrass can be related to non-target-site resistance mechanisms reducing absorption and translocation of the herbicide and causing reduced conversion or rapid degradation of florpyrauxifen-acid.

We previously reported that the mechanism of quinclorac resistance in Echinochloa crus-galli var. zelayensis may be closely related to ethylene biosynthesis and the detoxification of cyanide. Differences in EcCAS gene sequences and expression levels may result in higher capacity to detoxify cyanide in resistant biotypes, which may avoid cyanide accumulation and avoid more ethylene and cyanide production and then avoid damage. In the present study, we focused on the mechanism of resistance related to ethylene biosynthesis in E. crus-galli var. zelayensis. The fresh weight of susceptible and moderately resistant biotypes were significantly reduced after treatment with quinclorac. However, AOA, an ethylene biosynthesis inhibitor, reduced the impact of quinclorac. On pretreatment with AOA, ethylene production was significantly reduced in the three biotypes. The highly resistant biotype produced less ethylene compared to the other two biotypes. Three ACS and seven ACO genes, which are the key genes in ethylene biosynthesis, were obtained. The expression levels of EcACS-like, EcACS7, and EcACO1 varied in the three biotypes upon treatment with quinclorac, which could be manipulated by AOA. In summary, it is inferred that the expression of EcACS-like, EcACS7, and EcACO1 can be stimulated to varying extent after quinclorac treatment in three E. crus-galli var. zelayensis biotypes, which consequently results in varying levels of ethylene production. Lower expression of these three genes results in more resistance to quinclorac, which may also be related to quinclorac resistance in E. crus-galli var. zelayensis.

Managing weed seed production may help in reducing weed emergence and biomass in successive seasons in dry-seeded rice. Field experiments were conducted in 2012 and 2013 to ascertain the effect of delayed weed emergence, i.e., 0, 14, 28, 42, 56, and 70 days after sowing (DAS) on seed production ability of Digitaria ciliaris and Echinochloa crus-galli in two rice cultivars (PR115 with 125 days duration and PR114 with 145 days duration). Emergence of E. crus-galli was similar in both the cultivars, except at 42 DAS, where the emergence was higher in PR114 than PR115 during 2012. In PR114, D. ciliaris continued to emerge up to 56 DAS, although the increase was significant up to 28 DAS; the increased emergence of this weed was noticed up to 14 DAS in PR115. Weed biomass was also higher in PR114, although the rate of the decrease with respect to emergence time was similar in both the rice cultivars. D. ciliaris, when emerged with the crop, produced 11,820 seeds per plant in PR114, but seed production reduced by 25% in PR115. However, differences in seed production of E. crus-galli were noticed when this weed emerged between 14 and 42 DAS. An exponential model predicted that, for a 99% reduction in seed production of D. ciliaris, 42–45 days of crop advancement, while, for E. crus-galli, 21–33 days of crop advancement was required. Our study suggests that delaying the weed emergence in the crop and/or adopting better competitive rice cultivars can reduce the weed seed production substantially.

Barnyardgrass (Echinochloa crus-galli) is one of the top 15 herbicide-resistant weeds around the world that interferes with rice growth, resulting in major losses of rice yield. Thus, multi-herbicide resistance in barnyardgrass presents a major threat, with the underlying mechanisms that contribute to resistance requiring elucidation. In an attempt to characterize this multi-herbicide resistance at the proteomic level, comparative analysis of resistant and susceptible barnyardgrasses was performed using iTRAQ, both with and without quinclorac, bispyribac-sodium and penoxsulam herbicidal treatment. A total of 1342 protein species were identified from 2248 unique peptides by searching the UniProt database and conducting data analysis. Approximately 904 protein species with 4774 Gene Ontology (GO) terms were grouped into the categories of biological process, cellular component and molecular function. Among these, 688 protein species were annotated into 1583 KEGG pathways, with 980 protein species relating to metabolism and 93 relating to environmental information processing. A total of 292 protein species showed more than a 1.2-fold change in abundance in the resistant biotype relative to the susceptible biotype. Furthermore, herbicide treatment resulted in 157 protein species that showed more than a 1.2-fold change in the resistant biotype. Moreover, physiological analyses demonstrated an ecological fitness cost in the resistant biotype. Significance While some studies have shown a fitness cost to be associated with an altered ecological interaction, our understanding of the fitness costs associated with herbicide resistance are limited. Herein, physiological and proteomic analysis demonstrates herbicide resistance associated ecological fitness cost and potential mechanisms of herbicide-resistance in resistant biotypes of E. crus-galli. The results presented herein have revealed differences in ecological adaptation between resistant and susceptible biotypes in E. crus-galli and provide a fundamental basis enabling the development of new strategies for weed control. Lastly, this is the first large-scale proteomics study to examine herbicide stress responses in different barnyardgrass biotypes.

Since 2005, the evolution and spread of herbicide-resistant Echinochloa crus-galli biotypes have posed a serious threat to crop production in the Philippines. A comprehensive knowledge of E. crus-galli ecology and fecundity is fundamental in managing different biotypes of this weed. It was hypothesized that (a) high weed plant density produces more biomass and fertile seeds per unit area, (b) rice interference reduces the biomass and fecundity of the weed, and (c) a delay in weed emergence reduces the soil seed bank. In 2013, experiments were conducted in the wet season (WS) and dry season (DS), to understand the effect of E. crus-galli densities (40 and 80 plants m −2 ) on its growth, survival, and fecundity, with varying emergence times of 2, 15, 30, and 45 d after rice emergence (DARE). Relative to the weed plants grown without rice interference, E. crus-galli growth and seed production was lower in the presence of rice. Percent survival and plant height of E. crus-galli declined in a linear manner in the DS, and declined in a quadratic manner in the WS. Tiller number, inflorescence number, inflorescence biomass, and shoot biomass per plant declined in an exponential manner, with a delay in emergence of each cohort relative to rice. Across rice seeding rate, weed density, and emergence time, there was a linear relationship ( y = 110 x − 272 in the DS and y = 100 x − 220 in the WS) between E. crus-galli shoot biomass and the number of seeds plant −1 . Relative to the late-emerging weed cohorts, E. crus-galli seed production (1320–1579 seeds plant −1 ), 1000-seed weight (2.2–2.9 g), and seed yield (2808–2334 kg ha −1 ) were higher when seedlings emerged with the crop (2 DARE). None of the seedlings that emerged 45 DARE produced viable seeds. Seed germination of the first two cohorts (2 and 15 DARE) ranged from 84 to 91%. The delay in emergence of E. crus-galli beyond 30 DARE reduced the percentage of germinable and viable seeds, and increased the percentage of non-viable seeds produced plant −1 . The results suggest that cultural weed management approaches that delay the emergence of E. crus-galli can reduce weed biomass and seed production, and is thus valuable for preventing seed rain to the seed bank by noxious weed biotypes in the field.

Some plant GH3 genes are specifically induced by auxin within minutes and play important roles in plant growth and development. A GH3 cDNA was isolated from barnyardgrass. The gene, designated EcGH3.1 (Genebank Number: JN241678 ), has a full-length 1839 bp open reading frame predicted to encode a 67.82 kDa protein. Sequence alignment showed that EcGH3.1 is a GH3 homolog. Its transcript level in leaves and roots of quinclorac-susceptible (S) biotypes was higher than that in quinclorac-resistant (R) biotypes. After exposure to quinclorac in 30 min, EcGH3.1 expression was obviously decreased in leaves of S biotypes, but markedly increased in leaves of the R plants. EcGH3.1 with its different expression patterns can be considered a marker and applied to distinguish R and S biotypes. The results of this study also provide basic information for further research of the function of EcGH3 in barnyardgrass under herbicide stress .

Multiple-herbicide resistance (MHR) in barnyardgrass (Echinochloa crus-galli) is a threat to rice production. The Ala-205-Val mutation in acetolactate synthase (ALS) conferred resistance to several ALS inhibitors in the E. crus-galli population AXXZ-2; consequently, ALS-inhibitors were unable to control this noxious weed species. In the present study, the sensitivity to acetyl-coenzyme A carboxylase (ACCase) herbicides and other herbicides having different modes of action was evaluated to determine an effective strategy for chemical weed control. Compared with that of the reportedly sensitive population JLGY-3, the AXXZ-2 population showed differential resistance to three ACCase-inhibitors (cyhalofop-butyl, fenoxaprop-P-ethyl, and pinoxaden), in addition to quinclorac and pretilachlor. A novel substitution (Asp-2078-Glu) in ACCase was detected as the main target-site resistance mechanisms in the AXXZ-2 population. Structural modeling of the mutant ACCase protein predicted that Asp-2078-Glu confers resistance to three ACCase inhibitors by reducing the binding affinity between them and the ACCase protein. To the best of our knowledge, this is the first study to report that the novel Asp-2078-Glu mutation confers resistance to several ACCase inhibitors. Target-site mutations in ALS and ACCase were detected in this MHR population. Except for quinclorac, pretilachlor, ALS inhibitors, and the three ACCase inhibitors, a number of herbicides remain effective in controlling this MHR E. crus-galli population.

Biotypes of Echinochloa crus-galli var. formosensis with resistance to cyhalofop-butyl, an acetyl-CoA carboxylase (ACCase) inhibitor, have been found in dry-seeded rice fields in Okayama, Japan. We collected two lines with suspected resistance (Ecf27 and Ecf108) from dry-seeded rice fields and investigated their sensitivity to cyhalofop-butyl and other herbicides. Both lines exhibited approximately 7-fold higher resistance to cyhalofop-butyl than a susceptible line. Ecf108 was susceptible to penoxsulam, an acetolactate synthase (ALS) inhibitor. On the other hand, Ecf27 showed resistance to penoxsulam and two other ALS inhibitors: propyrisulfuron and pyriminobac-methyl. The alternative herbicides butachlor, thiobencarb, and bispyribac-sodium effectively controlled both lines. To examine the molecular mechanisms of resistance, we amplified and sequenced the target-site encoding genes in Ecf27, Ecf108, and susceptible lines. Partial sequences of six ACCase genes and full-length sequences of three ALS genes were examined. One of the ACCase gene sequences encodes a truncated aberrant protein due to a frameshift mutation in both lines. Comparisons of the genes among Ecf27, Ecf108, and the susceptible lines revealed that none of the ACCases and ALSs in Ecf27 and Ecf108 have amino acid substitutions that are known to confer herbicide resistance, although a single amino acid substitution was found in each of three ACCases in Ecf108. Our study reveals the existence of a multiple-herbicide resistant biotype of E. crus-galli var. formosensis at Okayama, Japan that shows resistance to cyhalofop-butyl and several ALS inhibitors. We also found a biotype that is resistant only to cyhalofop-butyl among the tested herbicides. The resistance mechanisms are likely to be non-target-site based, at least in the multiple-herbicide resistant biotype.

Natural, essential oil-based emulsions could be in future an alternative for synthetic herbicides. In this study, the possibility that foliar-applied caraway or peppermint essential oils (EO) can selectively inhibit the growth of Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass, a typical maize weed) but not that of maize plants was tested, in attempt to develop an eco-friendly botanical herbicide. The phytotoxic potential of oil-in-water emulsions of each EO with addition of commercial adjuvant, mainly composed of fatty acids methyl esters, was examined. Their effect on visible plants injuries, biomass accumulation, chlorophyll a fluorescence and changes to biochemical patterns of both the main crop (maize) and barnyardgrass via an untargeted metabolomic approach were studied. It was found that oil-in-water emulsion containing 2.5% of adjuvant and of caraway EO did not affect significantly the growth of maize plants, did not induce foliar symptoms and did not alter the status of the photosynthetic apparatus, as revealed by chlorophyll a fluorescence. On the contrary, this emulsion exerted significantly negative effects against barnyardgrass growth, inducing foliar injuries and reducing the photosynthetic efficiency of photosystem II. It was also found that the studied emulsions caused a series of biochemical changes in the plant tissues, with caraway emulsion being more phytotoxic, as compared to the peppermint EO-emulsion. In conclusion, oil-in-water emulsion containing 2.5% of caraway EO could be used in future as a foliar-applied botanical herbicide against barnyardgrass in maize cultivation.

Direct-seeded rice systems are increasing in Asia as farmers respond to the high labor cost and shortage of water. Echinochloa crus-galli is one of the most problematic and competitive weeds in direct-seeded rice systems. Because of concerns about excessive herbicide use, there is an interest in developing cultural weed management strategies. However, the design of such strategies requires a better understanding of the weed response to crop density, nutrition, and water regime. A study was therefore conducted in pots to determine the effect of water (flooded and aerobic), nitrogen (N) fertilization (0, 100, and 200 kg N ha −1 ), and rice density [0, 4 rice plants (≈20 kg seed ha −1 ), and 16 rice plants (≈80 kg seed ha −1 )] on the growth and reproduction of E. crus-galli . When grown alone, the growth and seed production of E. crus-galli were higher in flooded conditions than in aerobic conditions. However, no such differences were observed when E. crus-galli was grown with rice interference. E. crus-galli growth and seed production increased with increases in N rate. Irrespective of water regime and N rate, the growth and seed production of E. crus-galli declined with increases in rice density. At 100 kg N ha −1 , for example, E. crus-galli shoot biomass and seed production decreased by 84–86% and 82–87%, respectively, when grown with 16 rice plants compared with its growth without rice interference. The results suggest that growth and seed production of E. crus-galli can be greatly reduced by increasing rice seeding rate. However, there is a need to involve other weed management strategies to achieve complete control of E. crus-galli and other weed species.

During the 2006/07 and 2008/09 growing seasons in Southern Brazil, we evaluated crop selectivity and weed control efficacy of clomazone on rice when applied alone or in a mixture with other pre- and post-emergence herbicides (BRS Querencia variety). All herbicide treatments caused some degree of rice injury during both years; however, in no case was the injury still visible 21 days after application. Rice injuries were observed when application rates exceeded the recommended dose, and particularly when the herbicide was applied pre-emergence. Density reduction and panicle sterility served as measures of rice injury. Echinochloa crus-galli was the primary weed; it reduced rice yields by approximately 50% compared treated plots. In both growing seasons, clomazone herbicide (400 g ai ha−1) controlled the weed 87.0%–99.6%, and it provided 8.06 t ha−1 to 9.44 t ha−1 of rice yield.

The virulent strain B6 of Curvularia lunata was screened out from 65 fungus strains isolated from the diseased leaves of barnyardgrass ( Echinochloa crus-galli ). Greenhouse and field studies were conducted to evaluate the feasibility of the strain being exploited as a mycoherbicide for barnyardgrass control in paddy fields. The results of pathogenicity experiments showed that this strain was highly pathogenic to barnyardgrass at the 1- to 2.5-leaf stages. The fresh weight reduction increased with the increase of inoculated conidial concentrations and the prolongation of dew duration. Strain B6 provided excellent barnyardgrass control when it was applied at the concentration of 1×10 4 -1×10 6 conidia mL −1 in paddy fields with water layer. This strain was very safe to rice and the most plant species except wheat, barley and corn. Findings of this study indicated that this strain could be a potential mycoherbicide for barnyardgrass control in paddy fields in the future.

The negative effects of competition from barnyardgrass are generally accepted as an important cause of decreased rice growth and grain yield. However, little is known about the impact of barnyardgrass infestation on rice growth in paddy fields in relationship to contrasts in allelopathic traits and soil microbial community composition. We studied the response of rice growth and microbial feedback to barnyardgrass infestation using the allelopathic rice line PI312777 and the nonallelopathic cultivar Liaojing-9 grown with barnyardgrass and in barnyardgrass-infested soil in the field. Barnyardgrass infestation positively affected rice growth and reproduction in PI312777, but it did not do so in Liaojing-9. The chemical and biogeochemical characteristics of the soil did not differ significantly between the treatments and the controls. However, barnyardgrass infestation and mixed culture altered the microbiological properties of the soil, especially microbial biomass and community structure. The total PLFA concentration in Liaojing-9 and PI312777 in the barnyardgrass-infested soil and in mixed culture was higher than that of the control. The same trend occurred in the values of the bacteria: fungi ratio, Gram−:Gram+ ratio, stress level, and Shannon–Wiener index. A principal component analysis of the PLFA clearly separated the treatments. Our findings indicate that shifts in microbial community composition induced by barnyardgrass infestation may generate positive feedback on rice growth and reproduction in a given paddy system. From the perspective of plant–microbe–soil interactions, we should further evaluate the overall effect of barnyardgrass infestation on productivity and diversity in the paddy ecosystem.

Echinochloa species are problematic weed species in direct-seeded rice systems in Asia. Because of concern about the continuous use of single herbicides, cultural weed management strategies need to be developed to maintain the sustainability of direct-seeded rice systems. However, the design of such strategies requires an understanding of the differential responses of weeds to shade caused by crop interference. The effects of shade on growth and seed production of Echinochloa colona, Echinochloa crus-galli, and Echinochloa glabrescens were determined. Weeds of three Echinochloa species were grown continuously in full sunlight or in 50% or 25% of full sunlight, or started in full sunlight and transferred to 50% or 25% of full sunlight at 21 days after sowing. The results suggested that changes in shade regime did not affect the plant height of E. colona and E. glabrescens; however, shade reduced the height of E. crus-galli. Compared with the plants grown in full sunlight, 75% of continuous shade reduced E. crus-galli height by 22%. Shade reduced leaf, total shoot, and root biomass and seed production in all the weed species, if occurred during the early growth of the weeds. The weeds responded with increased leaf biomass ratio when grown in shade. Compared with full sunlight, continuous shade of 75% increased leaf biomass ratio by 90% in E. colona and this value was 25% in the other two species. The results of this study show that shade can reduce weed growth and seed production of Echinochloa species but it should not be considered as a stand-alone strategy to manage these weeds in rice. This highlights the need for the integration of other weed management strategies to achieve complete control of these species.

Lemongrass ( Cymbopogon citratus ) essential oil was identified by GC–MS for their major compound constituents; six compounds representing 92.59% of the total essential oil were identified. The main constituent was citral (76.00%). In a laboratory bioassay, high concentration of essential oil significantly inhibited germination and seedling growth of Echinochloa crus-galli and affecting α-amylase activity of seeds. In a glass house bioassay, essential oil at concentrations of 1.25, 2.5, 5 and 10% (v/v) was foliar-applied on E. crus-galli at 28 days after sowing at spray volume of 1000 L ha −1 . Observation of leaf wilt symptoms was noted at 6 h after treatment. Chlorophyll a, b and carotenoid content was decreased with concentrations of essential oil, indicating that essential oil interferes with photosynthetic metabolism. C. citratus essential oil caused an electrolyte leakage indicating membrane disruption and loss of integrity. Treated leaves exhibited an increase in thiobarbituric acid reactive substances (TBARS), suggesting lipid peroxidation. It is to conclude that essential oil is phytotoxic and could be utilized as a natural herbicide for future weed control.

This paper describes a dynamic simulation model that allows for comprehensive assessment of integrated weed management programmes for the control of annual barnyardgrass (Echinochloa crus-galli complex) in Philippine rice farming systems. The main outputs of the model include weed seed and plant densities and seasonal and annualised profit over the simulated planning horizon. Results broadly indicate that a mixture of chemical and non-chemical treatments provides good weed control in rice crops, and maximises long-term profit for systems where the main weed is annual barnyardgrass. However, the performance of this strategy is heavily influenced by crop establishment method and labour cost. At current labour cost and low weed density, the regular use of manual weeding is the most valuable primary form of weed control in rice farming systems, relative to herbicide application. Herbicide application becomes more profitable than manual weeding when labour costs increase or the population of barnyardgrass plants is not maintained at its optimal level. These results illustrate the value of the model for guiding the efficient control of annual barnyardgrass in rice crops in the Philippines.

Implications of increasing labour costs and the development of herbicide resistance for profitable weed management in Philippine rice farming systems are investigated. The study employs RIMPhil (Resistance and Integrated Management in the Philippines), a bioeconomic simulation model developed to provide a comprehensive assessment of integrated weed management programmes for the control of annual barnyardgrass ( Echinochloa crus-galli ) in rice crops. Results indicate that herbicide application will become increasingly economically attractive, relative to manual weeding, as labour cost increases. This is important since urban migration in the Philippines continues to increase the scarcity of rural labour. Results also show that the onset of herbicide resistance results in substantial losses in farm profit. It is worthwhile for farmers to take management actions to prevent or delay the onset of herbicide resistance, provided that these changes are effective and not too costly. The study highlights the complexity of decision making about integrated weed management on rice farms in the Philippines.

Echinochloa crus-galli, a C4 grass, is one of the world's most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8cm. A burial depth of only 0.4cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6tonha-1) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.

Despite increasing knowledge of jasmonic acid (JA) and salicylic acid (SA) as signaling compounds involved in the defense of rice against attacking microbes and insect predators, relatively little is known about their levels in the growth media and their interactions with other plant competitors. In present study we quantified JA and SA in a rice-barnyardgrass coexistence system followed by correlation analysis to access rice allelochemicals. Both rice and barnyardgrass biosynthesized JA and SA, but their contents varied greatly with species, tissues and coexistence. There was a positive correlation in contents between rice allelochemicals and JA in roots or SA in shoots. Endogenous JA was exuded from barnyardgrass roots eliciting the production of rice allelochemicals. SA was not detected in growth media as an exogenous signaling compound in a rice-barnyardgrass coexistence system, but SA content in rice shoots was an indicator for distinguishing the allelopathic rice traits from the non-allelopathic ones.

This study presents purification, activity characterization, and (1)H NMR study of the novel antifungal peptide EcAMP1 from kernels of barnyard grass Echinochloa crus-galli. The peptide adopts a disulfide-stabilized α-helical hairpin structure in aqueous solution and thus represents a novel fold among naturally occurring antimicrobial peptides. Micromolar concentrations of EcAMP1 were shown to inhibit growth of several fungal phytopathogens. Confocal microscopy revealed intensive EcAMP1 binding to the surface of fungal conidia followed by internalization and accumulation in the cytoplasm without disturbance of membrane integrity. Close spatial structure similarity between EcAMP1, the trypsin inhibitor VhTI from seeds of Veronica hederifolia, and some scorpion and cone snail toxins suggests natural elaboration of different functions on a common fold.

a b s t r a c t Since cucumber plants are mostly discarded as large waste after crop harvesting, allelopathy of cucumber plants was investigated for possible weed management options and utilization of the waste. Two potent growth inhibitory substances were isolated from an aqueous methanol extract of cucumber (Cucumis sativus L. cv. Phung Tuong) plants. These substances were determined as 9-hydroxy-4,7-megastigmadien- 9-one (HMO) and (6S,7E,9S)-6,9,10-trihydroxy-4,7-megastigmadien-3-one (THMO) by the analysis of MS, 1 H NMR spectra and optical rotation. HMO inhibited the growth of cress (Lepidium sativum L.) and Echinochloa crus-galli (L.) Beauv seedlings at concentrations greater than 0.3 and 1 M, respectively. THMO inhibited the growth of cress and E. crus-galli seedlings at concentrations greater than 1 and 3 M, respectively. The concentrations required for 50% growth inhibition on roots and shoots of cress and E. crus-galli were 2.4-29.3 M for HMO and 8.1-52.2 M for THMO. The endogenous levels of HMO and THMO in cucumber plants were 31.8 and 43.5 g g−1 dry weight, respectively. These results suggest that HMO and THMO may be the causal factors for the growth inhibitory effect of cucumber plants. Therefore, cucumber plants may be potentially useful for weed management options in an agricultural setting, such as a cover crop and soil admixture, which should be investigated further in the field.

Field experiments were conducted in Stuttgart, Arkansas, in 2007 and 2008 to evaluate cyhalofop application timing and adjuvant selection for Echinochloa crus-galli L. Beauv. (barnyardgrass) control in drill-seeded rice. In the application timing experiment, cyhalofop was applied at 1 d prior to flooding (PREFL) and at 7, 14, and 21 d post-flood (POSTFL) as single (314 g a.i./ha) or sequential application (first application at 314 g a.i./ha followed by a second application 14 days later at 213 g a.i./ha). In the adjuvant study, the adjuvants evaluated were non-ionic surfactant (NIS) at 0.25% v/v, crop oil concentrate (COC) at 1% v/v, methylated seed oil (MSO) at 1% v/v, 28% urea ammonium nitrate (UAN) at 2.5% v/v, combination of NIS or COC or MSO with UAN, a proprietary blend of MSO/organosilicone (OSL)/UAN at 2.5% v/v, and MSO/OSL/UAN applied with NIS or COC. All adjuvants applied with cyhalofop (314 g a.i./ha at 14 d after flood establishment) resulted in E . crus-galli control and rice yields comparable to cyhalofop alone. In 2007, a single application of cyhalofop controlled E . crus-galli 98–100% by the end of the season, except in the 14-d POSTFL timing (90%). In 2008, E . crus-galli plants were more robust, and control was inconsistent and less than in 2007 (10–91%). At the PREFL timing, sequential applications were needed to improve end-of-season E . crus-galli control. The 7-d POSTFL timing was one of the best single application timings for increased E . crus-galli control and rice yield. Delaying the cyhalofop application to 21-d POSTFL resulted in unacceptable E . crus-galli control of 10 and 46% with single and sequential programs, respectively. Average rice yield was reduced almost three-fold when the first cyhalofop application was at 21-d POSTFL compared with 7-d POSTFL.

The presence of energetic materials (used as explosives and propellants) at contaminated sites is a growing international issue, particularly with respect to military base closures and demilitarization policies. Improved understanding of the ecotoxicological effects of these materials is needed in order to accurately assess the potential exposure risks and impacts on the environment and its ecosystems. We studied the toxicity of the nitroaromatic energetic material 2,4-dinitrotoluene (2,4-DNT) on alfalfa (Medicago sativa L.), barnyard grass (Echinochloa crusgalli L. Beauv.), and perennial ryegrass (Lolium perenne L.) using four natural soils varying in properties (organic matter, clay content, and pH) that were hypothesized to affect chemical bioavailability and toxicity. Amended soils were subjected to natural light conditions, and wetting and drying cycles in a greenhouse for 13 weeks prior to toxicity testing to approximate field exposure conditions in terms of bioavailability, transformation, and degradation of 2,4-DNT. Definitive toxicity tests were performed according to standard protocols. The median effective concentration (EC50) values for shoot dry mass ranged from 8 to 229 mg kg- 1, depending on the plant species and soil type. Data indicated that 2,4-DNT was most toxic in the Sassafras (SSL) and Teller (TSL) sandy loam soils, with EC50 values for shoot dry mass ranging between 8 to 44 mg kg- 1, and least toxic in the Webster clay loam soil, with EC50 values for shoot dry mass ranging between 40 to 229 mg kg- 1. The toxicity of 2,4-DNT for each of the plant species was significantly (p ? 0.05) and inversely correlated with the soil organic matter content. Toxicity benchmark values determined in the present studies for 2,4-DNT weathered-and-aged in SSL or TSL soils will contribute to development of an Ecological Soil Screening Level for terrestrial plants that can be used for ecological risk assessment at contaminated sites. Crown Copyright © 2010.

Eight cultivars of rice (Oryza sativa L.) inhibited shoot and root growth of Echinochloa crus-galli when co-cultured with rice seedlings in a bioassay medium. Momilactone A and B were found in the bioassay medium of all rice cultivars, and concentrations of momilactone A and B in the medium were 0.21-1.5 and 0.66-3.8 micromol/L, respectively, indicating that all rice cultivars may secrete momilactone A and B into the medium. Exogenously applied momilactone A and B inhibited the growth of shoots and roots of E. crus-galli at concentrations greater than 30 and 1 micromol/L, respectively. The concentrations required for 50% growth inhibition of E. crus-galli shoots and roots, respectively, were 146 and 91 micromol/L for momilactone A and 6.5 and 6.9 micromol/L for momilactone B. Considering the growth inhibitory activity and concentrations found in the bioassay medium, momilactone A may have caused only 0.8-2.2% of the observed growth inhibition of E. crus-galli roots and shoots by rice. However, momilactone B in the medium was estimated to be able to cause 59-82% of the observed growth inhibition of E. crus-galli roots and shoots by the rice seedlings. In addition, the concentrations of momilactone B in the medium reflected the observed differences in the growth inhibition of E. crus-galli by the eight rice cultivars investigated. This suggests that the allelopathic activity of rice may depend primarily on the secretion level of momilactone B. Therefore, momilactone B may play a very important role in rice allelopathy.

Field experiments were conducted in 2008 and 2009 to determine growth and seed production of Echinochloa colona and Echinochloa crus-galli emerging at five intervals (0, 15, 30, 45, and 60 days after rice emergence, DARE) in aerobic rice seeded at 20- and 30-cm row spacing. Plant height of these two weed species was not influenced by the crop row, but it was influenced by the weed emergence time. Weeds of either species emerging until 30 DARE had greater biomass and more seeds under wide rows than under narrow rows, but row spacing had no effect on biomass and seeds of plants emerging later. In both crop row spacing treatments, delay in weed emergence until 45 DARE significantly reduced weed biomass. E. colona and E. crus-galli plants that emerged 60 DARE produced only 3 seeds plant-1 in 30-cm rows, whereas no seed was produced by these plants in 20-cm rows. Fitting a single linear function to the combined data for rows and weed emergence time gave a strong positive linear relationship between shoot biomass (g plant-1) and seed production (number plant-1) of these species, accounting for 94% and 93% variation in E. colona and E. crus-galli, respectively. These relationships can be used as a predictor of seed production in these species. Regardless of the weed species and weed emergence date, rice grain yields were greater in narrow rows than in wider rows. In the case of both weed species, rice grain yield improved significantly with each delay in weed emergence up to 45 DARE. The results of this study suggest that narrowing row spacing and controlling early weeds led to decreased weed growth and seed production, and increased grain yield in aerobic rice. Narrow crop row spacing and early weed control could be important components of integrated weed management strategies in aerobic rice.

Exserohilum monoceras (Drechsler) Leonard and Suggs is a potential biocontrol agent for the control of Echinochloa species. This fungus causes leaf blight in Echinochloa species, but does not damage rice. Phytotoxicity of the fungal fermented broth was evaluated through the bioassay and the active ingredients were preliminarily isolated by using silica gel column chromatography (CC) in this study. The most active fraction 5-III was obtained and analyzed by gas chromatography-mass spectrometry (GC-MS). The results show that 5-III consisted of many compounds, in which 36 compounds accounted for 94.24% of total peak area. Di-n-butyl phthalate (DBP) displayed the highest activity accounted for 9.24% of the total peak area, suggesting that DBP may be one of the main active compounds produced by E. monoceras.

Atmospheric CO 2 enrichment may impact arbuscular mycorrhizae (AM) development and function, which could have subsequent effects on host plant species interactions by differentially affecting plant nutrient acquisition. However, direct evidence illustrating this scenario is limited. We examined how elevated CO 2 affects plant growth and whether mycorrhizae mediate interactions between C 4 barnyard grass ( Echinochloa crusgalli (L.) Beauv.) and C 3 upland rice ( Oryza sativa L.) in a low nutrient soil. The monocultures and combinations with or without mycorrhizal inoculation were grown at ambient (400 ± 20 μmol mol −1 ) and elevated CO 2 (700 ± 20 μmol mol −1 ) levels. The 15 N isotope tracer was introduced to quantify the mycorrhizally mediated N acquisition of plants. Elevated CO 2 stimulated the growth of C 3 upland rice but not that of C 4 barnyard grass under monoculture. Elevated CO 2 also increased mycorrhizal colonization of C 4 barnyard grass but did not affect mycorrhizal colonization of C 3 upland rice. Mycorrhizal inoculation increased the shoot biomass ratio of C 4 barnyard grass to C 3 upland rice under both CO 2 concentrations but had a greater impact under the elevated than ambient CO 2 level. Mycorrhizae decreased relative interaction index (RII) of C 3 plants under both ambient and elevated CO 2 , but mycorrhizae increased RII of C 4 plants only under elevated CO 2 . Elevated CO 2 and mycorrhizal inoculation enhanced 15 N and total N and P uptake of C 4 barnyard grass in mixture but had no effects on N and P acquisition of C 3 upland rice, thus altering the distribution of N and P between the species in mixture. These results implied that CO 2 stimulation of mycorrhizae and their nutrient acquisition may impact competitive interaction of C 4 barnyard grass and C 3 upland rice under future CO 2 scenarios.

application/pdf, Our previous study revealed that salicylic acid (SA) accumulates in salt-stressed rice (Oryza sativa L. cv. Nipponbare) seedlings, and we hypothesized that the accumulation of SA might potentiate oxidative injury in rice seedlings since the inhibition of SA synthesis alleviated the growth inhibition under high salinity. To further clarify the action of SA under salt stress, we investigated the changes in the SA content, the activities of the antioxidative enzymes, and the effects of exogenous SA on barnyardgrass (Echinochloa crus-galli Beauv. var. formosensis Ohwi), a gramineous weed which shows lower SA content and is more salt tolerant than rice. In E. crus-galli seedlings exposed to high salinity, neither free nor conjugated SA content showed any increase, while the fresh weight of the shoot and chlorophyll fluorescence (FPSII) slightly decreased. When E. crus-galli seedlings were treated with salt after foliar application of SA, the absorbed SA resulted in the enhancement of the salt-induced growth inhibition and a striking reduction of the FPSII value. Catalase (CAT) and superoxide dismutase (SOD) activities of E. crusgalli seedlings were induced by the salt treatment. However, SA pre-treatment suppressed such an induction of CAT activity and further promoted SOD activity, both of which led to the elevation of the leaf hydrogen peroxide (H2O2) level. The present results suggested that enlargement of the cellular SA pool facilitates the generation of H2O2 through the suppression of CAT activity and through a remarkable promotion of SOD activity, and thereby enhances the oxidative injury caused by salt stress.

Soilin laboratory microcosmexperimentswas amendedwith dried and milledcrop residues of onion (Allium cepa L. cv. Mission) or garlic (A. sativa L. cv. California Early). The amendments, along with the additional factors of amendment concentration (0, 1 or 3% (w/w)) and soil temperature (23 or 39 8C), were evaluated with respect to germination of seeds of the weedy annual plants Echinochloa crus-galli (L.) Beauv. (barnyardgrass), Portulaca oleracea L. (common purslane), Sisymbrium irio L. (London rocket) and Solanum nigrum L. (black nightshade). Deleterious effects of seed exposure to 39 8C versus 23 8C were demonstrated in ECHCG, POROL, and SSYIR; and to increasing amendment concentration and the [concentration temperature] interaction in all four plant species tested (P < 0.05). The effect of garlic versus onion amendment was significant only in SOLNI, where garlic residues demonstrated more herbistatic and/or herbicidal activity. The results of these experiments showed that the garlic and onion plant residues were capable of causing significant reductions in seed germination during their decomposition in soil, but only at elevated (39 8C versus23 8C)soiltemperature.Attheagriculturallevel, activity ofthese residuescould be exploited as a component of integrated weed management using appropriate crop sequencing, and may extend utility of soil heating treatments (e.g. solarization) for weed

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.

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).

Alfalfa ( Medicago sativa L.) plants contain water-soluble substances that are autotoxic as well as allelopathic to other plants. Laboratory experimentation through a petri dish assay with imbibed seeds was conducted to evaluate the phytotoxic effects of alfalfa cv. “Vernal” leaf extracts, coumarin, trans -cinnamic acid, o -coumaric acid, and hydro-cinnamic acid on the seedling growth and anatomical responses of 6 day-old alfalfa and barnyard grass. With increasing concentration, the alfalfa leaf extracts significantly reduced root lengths of alfalfa and barnyard grass ( Echinochloa crus-galli , Beauv. var. oryzicola Ohwi). Coumarin, trans -cinnamic acid, o -coumaric acid, and hydro-cinnamic acid at 10 −4 M significantly reduced root lengths of alfalfa and barnyard grass. The root systems, especially root tips of alfalfa, were stunted and swollen by the aqueous alfalfa leaf extracts at 30 g l −1 and coumarin at 10 −3 M. This research suggests that alfalfa plant extracts significantly affected root growth and morphological differentiation of susceptible plants, resulting in reduction of their biomass in the presence of either autotoxic or allelopathic compounds. The results may have value in enabling weed control based on natural plant extracts.

Experiments were conducted to screen 23 known allelochemicals, including sinapic acid, and an equimolar mixture of the chemicals for potential allelopathy on barnyardgrass (Echinochloa crus-galli var. oryzicola), and to identify allelochemical(s) from hull extracts from three rice (Oryza sativa L.) cultivars. In a bioassay, the inhibitory effect was increased as the concentration of allelochemicals increased from 10−5 to 10−3 M. Ferulic, p-hydroxybenzoic, p-coumaric, and m-coumaric acids were the most active compounds and caused the greatest effect on seed germination, germination rate, and total seedling dry weight reduction. p-hydroxybenzoic acid (10−3 M; pH 4.1) showed the greatest inhibitory effect on the same parameters. HPLC analysis using three rice cultivars, Janganbyeo, Baekambyeo, and Labelle, showed that the concentration and composition of potentially allelopathic compounds depended upon the cultivar. Hull extracts from the allelopathic cultivar Janganbyeo contained higher levels of p-hydroxybenzoic acid than did those of the non-allelopathic cultivars Labelle and Baekambyeo. Nine compounds, including p-hydroxybenzoic acid (4.29 mg/g) in Janganbyeo, seven compounds including m-coumaric (0.43 mg/g) in Labelle, and five compounds including p-hydroxybenzoic acid (0.36 mg/g) in Baekambyeo, were detected. Preliminary identification by HPLC analysis resulted in peaks with retention times near those of standards, including p-hydroxybenzoic acid that was confirmed with EI/MS. It is suggested that these compounds may be, at least, a key factor in rice allelopathy on barnyardgrass, and the information presented may contribute to the development of naturally occurring herbicides.

Reinvestigation of the fermentation broth and mycelium of the coprophilous fungus Guanomyces polythrix, grown in static conditions, led to the isolation of several phytotoxic compounds, including two new naphthopyranone derivatives, namely (2S, 3R)-5-hydroxy-6,8-dimethoxy-2,3-dimethyl-2,3-dihydro-4H-naphtho[2,3-b]-pyran-4-one and (2S, 3R)-5-hydroxy-6,8,10-trimethoxy-2,3-dimethyl-2,3-dihydro-4H-naphtho[2,3-b]-pyran-4-one. The structures of the new compounds were established by spectral and chiroptical methods. In addition, the structure of 8-hydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester was unambiguously determined by X-ray analysis. The isolates caused significant inhibition of radicle growth of two weed seedlings (Amaranthus hypochondriacus and Echinochloa crusgalli) and interacted with both spinach and bovine brain calmodulins.

Optical active α-methylbenzyl p -tolylureas ( 7, 8 ) show diverse plant physiological properties. Experiments were conducted to evaluate the response of the optically active α-methylbenzyl phenylureas on root growth inhibition against rice and barnyard millet and to assess differential chiral responses of both plants from the viewpoints of activity, enantioselectivity, and cross intergenus response. A preference configuration to inhibit the root growth was not necessarily the same, and the toxicity and enantioselectivity were dependent on the substituent at the phenyl ring. To rice, the (R) -4-Pr ( 15 ) and (R) -4-Bu ( 23 ) derivatives exhibited the most potent activity with an I 50 value below 2 μM. To barnyard millet, similar to rice, the (R) -enantiomers with a lower alkyl group (2- tert Bu ( 25 ), 4-Pr ( 15 ), 2-isoPr ( 17 ), 3-Et ( 11 ), 4-Bu ( 23 ), 3-isoPr ( 19 ) and 4-Et ( 13 )) exhibited significant activity. The (R) -2-F-5-CF 3 ( 119 ) derivative was the most potent inhibitor, showing an I 50 value of 0.58 μM. The (S) -2-F ( 60 ), (S) -2,3-F 2 ( 90 ), (S) -2,5-F 2 ( 94 ) and (S) -4-COOEt ( 52 ) derivatives also inhibited the root growth of barnyard millet. Enantioselectivity and selective toxicity were quite high. Only chiral pairs of the 3-Me ( 5, 6 ) and 4-Me ( 7, 8 ) derivatives exhibited a cross intergenus response between rice and barnyard millet; rice was more affected by the (R) -enantiomers and barnyard millet by the (S) -enantiomers. Differential chiral responses including enantioselectivity and cross intergenus response between Oryza and Echinochloa plants against optically active α-methylbenzyl phenylureas were indicated in this study.

The interaction of two postemergence herbicides, propanil (3′4′-dichloropropioanilide) and pyribenzoxim-{benzophenone O -[2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoyl]oxime, code name; LGC-40863}, was investigated using barnyardgrass [ Echinochloa crusgalli (L.) Beauv.] at the four-leaf stage. Propanil at rates from 0.5 to 4 kg ai ha −1 was antagonistic to pyribenzoxim, particularly at higher doses of propanil. Propanil treatment during the period of 1 day before through 5 days after pyribenzoxim treatment was antagonistic. This antagonism was evident only when the two herbicides were applied to the same leaf. No antagonism occurred when the two herbicides were applied to separate leaves. Foliar absorption of [ 14 C]pyribenzoxim was about 32% of the total applied at 48 h after treatment and was not affected by propanil. Translocation of radiolabel out of the treated leaf was about 11% of the total absorbed 48 h after treatment, but translocation was reduced to 3.5% when propanil was applied to the same leaf. Translocation of radiolabel increased to 15% when propanil was applied to an adjacent leaf. Chlorophyll fluorescence analysis showed that propanil decreased the quantum yield of the treated leaf, but did not affect the untreated leaves of the same plant. When the pyribenzoxim-treated leaf was excised, within 5 days after treatment, plants were not completely controlled. Thus, translocation within 5 days of treatment is essential for pyribenzoxim activity. These data suggest that propanil decreases whole plant activity of pyribenzoxim in barnyardgrass by reducing translocation to adjacent tissues.

The mechanism of selectivity of the auxin herbicide quinclorac was studied in susceptible and resistant biotypes of Echinochloa hispidula and E. crus-galli ; in grass species of different susceptibility like Brachiaria platyphylla, Setaria viridis, E. colonum , and Digitaria sanguinalis ; and in tolerant crop rice ( Oryza sativa cv. Thaibonnet). No significant differences in uptake, translocation, or metabolism of quinclorac between resistant and sensitive grasses were found. Hence, the mechanism of selectivity is target-site-based. It has been demonstrated that cyanide, which accumulates as a coproduct during stimulation of ethylene biosynthesis, is the primary phytotoxic principle in the herbicidal mode of action of quinclorac in E. crus-galli (K. Grossmann and J. Kwiatkowski, 1995, Pestic. Biochem. Physiol. 51, 150). Following root treatment of plants at the third leaf stage with 100 M quinclorac in hydroponics, the reductions in shoot growth of plants were closely correlated with the stimulation of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and with subsequent increases in endogenous concentrations of ACC and cyanide. When compared quinclorac with other auxin herbicides including quinmerac, α-naphthaleneacetic acid and dicamba, lower ACC and cyanide levels and correlated lower growth effects were found after treatment of D. sanguinalis . In quinclorac-resistant grass species and biotypes, ACC synthase activity was not induced and plants exhibited no significant changes in ACC and cyanide levels. Thus, the selective induction of ACC synthase activity, which ultimately leads to cyanide accumulation in the tissues of susceptible plants, plays the primary role for the selectivity of grasses toward quinclorac. This selectivity could be at the level of quinclorac perception or subsequent signal transduction via the auxin pathway leading to regulation of gene expression or posttran scriptional de novo enzyme synthesis. In rice, tolerance to quinclorac could be additionally favored by a higher β-cyanoalanine synthase activity, the main HCN-detoxifying enzyme.

Isoxaflutole (5- cyclopropyl isoxazol-4-yl-2-mesyl-4-trifluoromethylphenyl ketone ) is a novel herbicide for preemergence control of a wide range of important broadleaf and grass weeds in corn and sugarcane producing characteristic foliar bleaching activity in susceptible species prior to plant death. Following either foliar or root uptake, isoxaflutole is rapidly converted to a diketonitrile derivative ( 2-cyclopropyl-3-(2-mesyl-4-trifluoromethylphenyl)-3-oxopropanenitrile ) by opening of the isoxazole ring. This diketonitrile undergoes degradation to a benzoic acid derivative ( 2-mesyl-4-trifluoromethyl benzoic acid ) in treated plants and the extent of this degradation is correlated to the degree of susceptibility, being most rapid in tolerant corn and slowest in susceptible Abutilon theophrasti . Following a preemergence application of [ phenyl (U)- 14 C]-isoxaflutole, equivalent to 250 g ai ha −1 only 10% of the extracted 14 C activity was the active diketonitrile in corn, compared to 90% in A. theophrasti . The rate of diketonitrile degradation was intermediate in moderately susceptible Ipomea spp. The foliar symptoms are associated with an accumulation of phytoene in treated leaves of Brassica kaber , typical of herbicidal inhibitors of phytoene desaturase. However, neither the diketonitrile derivative nor isoxaflutole inhibits the desaturation of radiolabeled phytoene by a microsomal extract of carrot cell cultures. However, the diketonitrile does inhibit 4-hydroxyphenylpyruvate dioxygenase, preventing the biosynthesis of homogentisate, the precursor of plastoquinone and α-tocopherol. The content of both these prenylquinones in emerging leaves of isoxaflutole-treated plants decreases prior to the accumulation of phytoene and the decrease in carotenoids. The mode of action of isoxaflutole is suggested to be due to an indirect inhibition of phytoene desaturase resulting from the absence of plastoquinone, an essential cofactor for the desaturase.

A culture broth of Nigrospora sacchari showed strong herbicidal activity in treatment of intact greenhouse-grown plants. Three lactones were isolated from the culture broth. The major compound, which exhibited the most significant effect of the fungal metabolites in the assay procedures, was identified as (+)-phomalactone, 6-(1-propenyl)-5,6-dihydro-5-hydroxy-2H-pyran-2-one. Others were 5-[1-(1-hydroxybut-2-enyl)]-furan-2-one and 5-[1-(1-hydroxybut-2-enyl)]-dihydrofuran-2-one. These fungal metabolites were investigated for their herbicidal effects in an electrolyte leakage assay and the results obtained appeared to indicate that the herbicidal damage was caused by cellular disruption. Phomalactone caused remarkable and rapid electrolyte leakage on cucumber cotyledon discs at concentrations higher than 50 ppm.

Selective accumulation of cyanide, derived from the stimulation of 1-aminocyclopropane-1-carboxylic acid (ACC) production in ethylene biosynthesis, was demonstrated to be the primary mode of action of the auxin herbicide quinclorac in the control of barnyard grass in rice ( Pestic. Biochem. Physiol. 51, 150 (1995)). The influence of quinclorac on the induction of ACC synthase activity was studied in both plant species. After hydroponic treatment of barnyard grass plants ( Echinochloa crus-galli L.) with 10 and 100 μM of the herbicide, a transient rise in ACC synthase activity and concomitantly ACC levels was detectable in the root tissue as early as 1 h. Peak levels of an approximately threefold increase, relative to control tissue, were observed at 3 h. Since quinclorac did not influence the in vitro activity of ACC synthase, the compound appears to interfere with the induction process of the enzyme. In the shoot tissue, ACC synthase activity began to increase after 2 to 3 h and proceeded during the investigation period of 7 h, dependent on the herbicide concentration. The rise in ACC levels and ethylene formation preceded that of ACC synthase activity. Interorgan transport of ACC from the root to the shoot is assumed. When detached shoots and roots of barnyard grass were treated with quinclorac in vitro, ACC synthesis was stimulated only in the root tissue. Since no qualitative or quantitative differences between the metabolism of quinclorac in barnyard grass shoot and root tissue were found, the principal site of interaction of quinclorac with ACC synthase is localized in the root tissue. In the shoot tissue of intact plants, ACC synthase activity appears to be stimulated indirectly by quinclorac-induced ACC from the root and its oxidation product, cyanide. This is concluded from experiments with detached shoots of barnyard grass. Treatment with ACC or KCN via the vascular system led to an increase in ACC synthase activity in the shoot tissue. Intact plants or detached shoots and roots of rice ( Oryza sativa L. cv. Thaibonnet) did not respond to quinclorac with changes in ethylene formation, ACC synthase activity, and ACC levels. It is suggested that species-selective induction of ACC synthase activity is implicated in the mechanism of quinclorac selectivity between barnyard grass and rice.

The suitability of 12 graminaceous weeds of ricefields as host plants for two rice leaffolders, Cnaphalocrocis medinalis (Guenee) and Marasmia patnalis Bradley (Lepidoptera: Pyralidae) was compared to a susceptible (IR36) and a moderately resistant (TKM6) rice variety in laboratory and greenhouse tests. Although rice was the most preferred host of the two leaffolder species, their responses to the test weeds varied significantly. Cnaphalocrocis medinalis responded better to most of the test weeds than did M. patnalis , suggesting a wider host range for C. medinalis . Third instar larval orientation and settling, and food consumption and assimilation of C. medinalis on Leersia hexandra, Echinochloa crus-galli, Echinochloa glabrescens, Echinochloa colona , and Leptochloa chinensis were comparable to those on susceptible IR36 and moderately resistant TKM6 rice varieties. First instar larval settling of C. medinalis on Leersia hexandra was similar to that on IR36. C. medinalis growth on Eleusine indica and IR36 was comparable. Oviposition by C. medinalis on IR36, TKM6, Eleusine indica , and Leptochloa chinensis was high and similar. Performance of M. patnalis on Leersia hexandra was better than on other test weeds but not similar to IR36 or TKM6 varieties in all the behavioral and physiologial criteria used.

Rifampicin-resistant mutants of two plant-growth-promoting rhizosphere bacteria, Pseudomonas fluorescens strain PsIA12 and the associative, non-symbiotic Rhizobium leguminosarum bv. trifolii strain R39, were inoculated with different crops in field experiments. Soil from these sites was collected after harvest. Non-inoculated maize, pea, lupine and two weeds (Amaranthus retroflexus, Echinochloa crus-galli ) were subsequently grown in this soil in the greenhouse and tested for colonization with Pseudomonas strain PsIA12 and Rhizobium strain R39. The Rhizobium strain was able to re-establish in the rhizosphere of the plants without nodulation in between, even after dry storage of the soil up to 12 months. It could even colonize a second subsequent plant generation. Highest cell numbers were detected in legumes (mean value log 5.0 cfu · g root -1 ), followed by maize (log 4.3 cfu · g root -1 ) and the weeds ( -1 ). Rhizosphere colonization was modified by the inoculated precrop. The Pseudomonas strain was not able to re-establish cell numbers higher log 3.0 cfu · g root -1 in the rhizosphere.

Resistance of barnyardgrass ( Echinochloa crus-galli ) to propanil, an important herbicide for controlling weeds in rice, has been discovered in Arkansas. Laboratory studies were conducted using resistant and susceptible barnyardgrass biotypes and 14 C-radiolabeled propanil to determine if differential adsorption/translocation of propanil was responsible for resistance and to determine if an altered propanil binding site existed in the resistant biotype. Absorption and translocation of propanil were not significantly different in the resistant and susceptible barnyardgrass biotypes. Chlorophyll fluorescence data from leaf disks exposed to propanil showed that the herbicide binding site in the electron transport chain of PS II was also not altered in the resistant biotype. This biotype was not cross-resistant to other herbicides that inhibit PS II(atrazine, diuron, fluometuron, or linuron) because both biotypes had equal mortality rates when treated with recommended concentrations of these herbicides in the greenhouse, and low levels of atrazine (50 μM ) totally inhibited PS II in chlorophyll fluorescence tests of both biotypes. Thus, propanil resistance in this barnyardgrass biotype is not due to differential absorption, translocation, or modification of the herbicidal site of action.

Root application of the quinolinecarboxylic acid herbicide quinclorac to barnyard grass ((Echinochloa crus-galli (L.) P. Beauv.) caused inhibition of shoot growth accompanied by chlorosis and necrosis. After 1 day of exposure, cyanide levels in the shoot tissue increased according to the concentration of the herbicide and the time of its application and closely correlated with the reduction in shoot fresh weight. Four days after the application of 10 and 100 μM quinclorac, the respective cyanide levels in the shoot tissue were approximately two and three times higher than controls and reached a maximum of 40 μM. Increases in β-cyanoalanine synthase activity, the main HCN detoxifying enzyme, ethylene production, and in the endogenous levels of 1-aminocyclopropane-1-carboxylic acid (ACC) preceded cyanide accumulation, When ACC was exogenously supplied to detached shoots of barnyard grass via the vascular system, its accumulation within the tissue coincided with increases in ethylene formation and cyanide content. Both metabolites of ACC appeared to be formed in stoichiometrically equivalent amounts. Root treatment of intact plants with KCN caused concentration-dependent increases in the levels of cyanide found in the shoot tissue which inversely correlated with the changes in fresh weight. The concentrations of quinclorac or KCN applied via the roots which led to twofold increases in the cyanide levels of the shoots had similar effects on the shoot fresh weight, causing reductions of nearly 30%. The phytotoxic symptoms, chlorosis and necrosis, were also similar. In contrast, phytotoxic tissue sensitivity to ethylene released by applied 2-chloroethylphosphonic acid (ethephon) was only very low. It is concluded that cyanide, derived ultimately from quinchlorac-stimulated ACC synthesis, is a causative factor in the herbicidal effects observed in the shoots of barnyard grass.

The effect of interspecific and intraspecific competition and salinity on the growth and distribution of Echinochloa crus-galli (L.) Beauv. was investigated in the field and under laboratory conditions. A de Wit replacement series indicated that the total dry mass of Echinochloa crus-galli decreased significantly with an increase in the density of Atriplex triangularis Willd. Under laboratory conditions, salinity had a greater inhibitory effect on the above-ground biomass production of E. crus-galli than did an increase in the proportion of the competitor, A. triangularis. Increasing salinity levels caused a decrease in the total above-ground biomass production of E. crus-galli and probably limited its distribution in the more stressful habitats. Laboratory experiments indicated that within the salinity range tested, Echinochloa could compete successfully with the more salt tolerant Atriplex. In the field, we found that the distribution of E. crus-galli along a salinity gradient was limited by salinity stress at high salinities and by competition from A. triangularis at low salinities.

Summary The quinolinecarboxylic acid quinclorac, which is structurally related to natural auxins, is a rice herbicide with selective activity against dicot and monocot weeds. As demonstrated for monocot and dicot species, stimulation of ethylene production by the herbicide was positively correlated with its phytotoxic effect. Treatment of susceptible barnyardgrass plants (Echinocloa crus-galli) at the second leaf stage with 20 µtg/plant (approx. 3 × 10−5 mol·L−1) quinclorac via the root appeared to specifically induce ethylene biosynthesis in the root tissue. However, the 1-aminocyclopropane-1-carboxylic acid (ACC) produced and its derivatives predominantly accumulated in the shoot tissue, where levels of ACC, N-malonylACC (MACC), ethylene formation, and HCN increased up to 3-, 60-, 5-, and 3-fold, respectively. Concomitantly, intact root tissue was 50-fold less susceptible to damage by quinclorac than intact shoot tissue. The observed HCN level in the latter tissue went up from 12 to 38 µmol·L−1 after treatment with quinclorac. Among the other phytohormones analyzed, only the immunoreactive 3-indoleacetic acid content increased in shoot tissue. Additional treatment with the ACC synthase inhibitor aminoethoxyvinylglycine decreased quinclorac-induced ethylene production and the phytotoxic effects on shoots of barnyardgrass. Quinclorac-treated rice plants (Oryza sativa) showed no notable changes in ethylene production and endogenous ACC, MACC, HCN and immunoreactive phytohormone contents and, shoots of rice plants were 200-fold less susceptible to damage by quinclorac than those of barnyardgrass. In comparison with quinclorac, 2,4-dichlorophenoxyacetic acid (2,4-D) caused considerably lower increases in ethylene production and endogenous levels of ACC, MACC and HCN in barnyardgrass shoots. This coincided with a 30-fold lower phytotoxic effect of 2,4-D on this plant part. Furthermore, exogenously applied KCN caused phytotoxic symptoms on barnyardgrass very similar to those exerted by quinclorac. We suggest a possible relationship between phytotoxic susceptibility and accumulation of endogenous toxic HCN formed as a co-product during quinclorac-stimulated ethylene biosynthesis.

The competition for light and nitrogen between rice (Oryza sativa L.) and barnyardgrass (BYG; Echinochloa crus-galli (L.) Beauv. ssp. hispidula) in an irrigated paddy is described by means of simulation. (1) Growth and development of both rice and BYG are simulated with the same plants model which accounts for tiller production and for mass growth of leaf, culm, root, and grain on each tiller. (2) Competition for light depends on the plant height and the vertical leaf area distribution, and is expressed as the share of incident light absorbed by rice and BYG, respectively. (3) Competition for nitrogen is based on the proportion of root space explored by rice and BYG and is estimated from the respective root mass. (4) The model, originally developed for rice, is validated here for BYG planted in monoculture at different densities. (5) The model predictions on biomass growth of competing rice and BYG are compared to field data collected in a replacement experiment. (6) The effect of BYG competition on rice yield is demonstrated for various rice and BYG planting densities.

Acetyl coenzyme A carboxylase (ACCase), the target site inhibited by two groups of herbicides, the aryloxyphenoxypropionates and cyclohexanediones, was extracted and partially purified from rice (Oryza sativa LeMont L.), barnyardgrass (Echinchloa crusgalli (L.) Beauv.) and sprangletop (Leptochloa fascicularis (Lam.) Gray). This was to determine whether the lack of inhibition of rice to three grass toxic herbicides, haloxyfop, fenoxaprop and sethoxydim is due to a differential selectivity at the enzyme level. Incorporation ration rates of NaH14CO3 into malonyl coenzyme A (CoA) were linear up to 8 min and maximum specific activity was obtained at 0.1–0.2 mg protein. Inhibition of ACCase from rice and the two weed species by haloxyfop and fenoxaprop showed differences that disappeared with higher concentrations of herbicide. I50 values for haloxyfop inhibition of ACCase from rice, barnyardgrass and sprangletop were 3.50, 2.50 and 2.40 μM, respectively. I50 values for fenoxaprop inhibition of enzyme from rice, barnyardgrass and sprangletop were 0.63, 0.33 and 0.33 μM, respectively. ACCase from rice was more sensitive to sethoxydim than from the two grass weeds. I50 values for rice, barnyardgrass and sprangletop were 6.18, 6.76 and 7.23 μM, respectively. These results suggest that selectivity of fenoxaprop and haloxyfop in rice may be in part attributable to a decreased sensitivity of ACCase, but this cannot totally account for the margin of tolerance exhibited in the field.