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Bromacil was introduced at the beginning of the 1960s for PRE and early POST control of grasses and broadleaf weeds, particularly in citrus (Rutaceae spp.) orchards and pineapple [Ananas comosus (L.) Merr.] plantations as well as in noncultivated areas. Both the acidic form of bromacil and its lithium salt are highly soluble in water; the herbicide is moderately to highly persistent in the soil with a half-life from 60 d to 8 mo and is prone to percolate in the soil and reach groundwater. In Costa Rica, bromacil was registered for both citrus and pineapple, but in recent years its major use has been in pineapple. An average of 60,000 kg of active bromacil per year were imported before its banning in 2017. Pineapple is grown in more than 40,000 ha; the recommended rate of bromacil was 1.6 to 3.2 kg ha−1. In a survey conducted by the National University between 2001 and 2004, bromacil was the most frequently found pesticide, at levels between 0.5 and 20 µg L−1, in water springs and wells in the pineapple-growing area of the Caribbean side of Costa Rica. Further studies conducted more recently also documented the presence of bromacil in the ground and surface water in areas where pineapple is planted. The local standard for the quality of drinking water of 2015 established maximum acceptable values of 0.1 µg L−1 and 0.5 µg L−1 for a single pesticide and for the sum of all pesticides present, respectively, but it was amended for bromacil to comply with requirements determined by the Constitutional Court to “non-detectable by method.” This paper provides an account of the scientific and administrative considerations for the banning of bromacil that occurred on May 24, 2017.

Background Tea, one of the most important commercial crops on earth, is strongly affected by weeds on productivity and quality. Bioherbicides are shedding new light on weed control in tea gardens in an economical and safe manner. Results A pathogenic strain SYNJC-2-2 was isolated from diseased leaves of a noxious weed, goosegrass (Eleusine indica) from a tea garden in Zhejiang Province, China. It was identified as the fungal species Bipolaris bicolor based on the morphological characteristics and phylogenetic analysis. The potential of the B. bicolor strain SYNJC-2-2 as a bioherbicide was assessed by determining its efficacy to control weeds and selectivity to crops, its infection process and the influence of environmental conditions on conidial production and germination. The ED90 (effective dose of conidia resulting in 90 disease index) of SYNJC-2-2 on goosegrass was 2 × 104 conidia mL-1 . Additionally, three Poaceae weeds, Setaria viridis, Microstegium vimineum and Pennisetum alopecuroides, were also extremely susceptible to SYNJC-2-2. SYNJC-2-2 was safe to 14 out of 17 crop species in 9 families, especially tea plants. Conidial germination, hyphal growth and appressorial formation occurred within 3 to 6 h on goosegrass leaves. Hyphae invaded leaf tissues mainly through epidermal cell junctions and cracks, causing cell death and necrotic lesions within 2 days on inoculated leaves and killing goosegrass plants within 7 days. Furthermore, SYNJC-2-2 has a strong adaptability to environmental variables and high conidial production capacity on goosegrass juice agar media. Conclusion B. bicolor strain SYNJC-2-2 has the potential to be developed as a bioherbicide for controlling goosegrass, especially in tea gardens. This article is protected by copyright. All rights reserved.

Water is one of the main dispersal agents of plant seeds and influences plant population dynamics and community structure. Although a large proportion of paddy fields are subjected to irrigation, limited research has addressed weed seed dispersal via water in rice-based systems. In this study, safranin T-dyed Beckmannia syzigachne seeds were released and their movement was tracked to characterize their dispersal dynamics via water in an irrigation canal and in a rice field. B. syzigachne seeds, floating on the water surface, moved from their release point at the canal entrance via irrigation water along the irrigation canal. A well-simulated Gaussian plume model indicated that the seed dispersal of B. syzigachne conformed to a leptokurtic distribution, and the peak dispersal kernel showed that seeds moved along the irrigation water flow to approximately 800–1000 m away from the release point 36 h after release into the canal. When seeds were released in the center of a flooded field, a total of 60% of the released seeds were water-dispersed to the northwest corner by the southeast prevailing monsoon wind within 72 h. The well-fitted Gauss 2D-model illustrated the widening of the seed distribution range with time and dispersal pattern with an accumulation center in the field. Our study is the first to show that buoyant weed seeds are mainly dispersed by irrigation water in both the canal and field and that the water dispersal of seeds influences the spatial deposition and distribution of the weed seed bank and strongly affects weed occurrence patterns in irrigated fields.

Angiosperms are believed to have emerged initially in the tropics and expanded their distribution range poleward through diverse mechanisms, for example polyploidization‐driven cold tolerance evolution. Reversed expansion from temperate to pan‐tropic climates through a polyploidization‐driven shift in heat tolerance remains largely unknown. Here, we found autopolyploidy in relation to the global expansion of Solidago canadensis from its temperate‐climate native range in North American to hot‐summer climate in an introduced range. Our cytogeographical study of 2,062 accessions from 471 locations worldwide demonstrates that ploidy levels correlate negatively with latitude and positively with average temperature. An isotherm‐dependent shift of the climate niches at the threshold of 20°–24°C between geo‐cytotypes can be attributed mainly to autopolyploidy‐driven differentiation of heat tolerance; only polyploids and not diploids are able to complete sexual reproduction, germinate, and grow in the hot‐summer climate of low latitudes. Ploidy‐dependent fertility appears to play a key role in the hot‐summer introduced range in the northern hemisphere through both pre‐adaptation and rapid post‐introduction adaptive evolution of delayed flowering and improved heat tolerance during embryo development. The MaxEnt model predicts continued expansion of this plant species under global change. These results provide new insights into the mechanisms governing autopolyploidy‐driven backward range expansion of plant species from temperate origins.

Pollen-mediated transgenic flow of herbicide resistance occurs bidirectionally between transgenic cultivated rice and weedy rice. The potential risk of weedy traits introgressing into hybrid rice has been underestimated and is poorly understood. In this study, two glufosinate-resistant transgenic rice varieties, hybrid rice (F1), and their succeeding generations (F2-F4) were planted for 3 years in field plots free of weedy rice adjacent to experimental weedy-rice fields. Weedy-rice-like (feral) plants that were both glufosinate-resistant and had red-pericarp seed were initially found only among the F3 generations of the two glufosinate-resistant transgenic hybrid cultivars. The composite fitness (an index based on eight productivity and weediness traits) of the feral progeny was significantly higher than that of the glufosinate-resistant transgenic hybrid (the original female parent of the feral progeny) under monoculture common garden conditions. The hybrid rice progeny segregated into individuals of variable height and extended flowering. The hybrid rice F2 generations had higher outcrossing rates by pollen reception (0.96-1.65%) than their progenitors (0.07-0.98%). The results show that herbicide-resistant weedy rice can rapidly arise by pollen-mediated gene flow from weedy to transgenic hybrid rice, and their segregating pollen-receptive progeny pose a greater agro-ecological risk than transgenic varieties. The safety assessment and management regulations for transgenic hybrid rice should take into account the risk of bidirectional gene flow.

Liriope spicata (Thunb.) Lour has a unique LsEPSPS structure contributing to the highest-ever-recognized natural glyphosate tolerance. The transformed LsEPSPS confers increased glyphosate resistance to E. coli and A. thaliana. However, the increased glyphosate-resistance level is not high enough to be of commercial value. Therefore, LsEPSPS was subjected to error-prone PCR to screen mutant EPSPS genes capable of endowing higher resistance levels. A mutant designated as ELs-EPSPS having five mutated amino acids (37Val, 67Asn, 277Ser, 351Gly and 422Gly) was selected for its ability to confer improved resistance to glyphosate. Expression of ELs-EPSPS in recombinant E. coli BL21 (DE3) strains enhanced resistance to glyphosate in comparison to both the LsEPSPS-transformed and -untransformed controls. Furthermore, transgenic ELs-EPSPS A. thaliana was about 5.4 fold and 2-fold resistance to glyphosate compared with the wild-type and the Ls-EPSPS-transgenic plants, respectively. Therefore, the mutated ELs-EPSPS gene has potential value for has potential for the development of glyphosate-resistant crops.

Background Weedy rice, as one of the worst paddy field weeds worldwide, bears vigorous seedlings and dominantly competes with cultivated rice causing serious crop yield losses. To elucidate the causes of its stronger seedling vigour endowing its dominant competition with cultivated rice, comparative studies on seedling growth characteristics were conducted among six weedy rice biotypes and the two indica and japonica cultivars Shanyou-63 (SY-63) and Zhendao-8 (ZD-8), respectively, in the greenhouse. Results Weedy rice emerged 2 to 3 days earlier, rapidly grew 1.3-1.7 cm taller daily, produced more secondary adventitious roots and greater aboveground fresh biomass than cultivated rice. Moreover, weedy rice exhibited greater photosynthetic pigment content, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, and chlorophyll fluorescence kinetic parameters. An enhanced overall photosynthetic activity in weedy rices was attributed to the combined action of a larger antenna, more active reaction centres and higher quantum yield for electron transfer beyond QA . Conclusions Enhanced photosynthesis of weedy rice at the seedling stage should be the main factor for leading to strong competitive dominance over cultivated rice. © 2016 Society of Chemical Industry.

In perennial crops like coffee, glyphosate drift exposure can occur multiple times during its commercial life span. Due to limited glyphosate degradation in higher plants, a potential accumulation of glyphosate could lead to increased biological effects with increased exposure frequency. In this study, we investigated glyphosate translocation over time, and its concentration and biological effects after single and multiple simulated spray-drift exposures. Additionally, shikimic acid/glyphosate ratios were used as biomarkers for glyphosate binding to its target enzyme. Four weeks after the exposure, glyphosate was continuously translocated. Shikimic acid levels were linear correlated with glyphosate levels. After two months, however, glyphosate appeared to have reduced activity. In the greenhouse, multiple applications resulted in higher internal glyphosate concentrations. The time of application, however, was more important regarding biological effects than the number of applications both in the greenhouse and in the field. In the field, berry yield, the most important biological response variable, was reduced 26% by the first out of four sequential applications of glyphosate at 64 g a.e. ha −1 each. The three subsequent applications did not reduce yield any further.

The objective of this research was to study the relationship between the fatty acid content and the altitude of orchards and fruit maturity stage of avocados (Persea americana Mill. cv. Hass) at different locations in the department of Antioquia (Colombia). Orchards between 1,340 and 2,420 m a.s.l. were selected and the fatty acid profile and content of the fruits were analyzed. Oleic acid showed the highest percentage for all of the locations and its percentage decreased drastically at lower altitudes, meanwhile the percentage of palmitoleic and linoleic acids increased in these orchards. The oleic/palmitoleic, linoleic/palmitoleic, and oleic/linoleic indexes increased significantly at higher altitudes. Palmitoleic acid increased significantly with the maturity stage (dry matter content) of the avocados for all of the locations. Some fatty acids showed a high linear correlation with the fruit maturity stage, varying the type of acid or index with altitude. The fatty acid content is a variable to consider in future studies for a protected designation of origin (PDO), due to the close relationship observed with the geographical growing area and its importance to human health. More assessments must be taken over the course of years and harvests with more contrasting environments in order to obtain more robust information and feed the model.

Cyperus difformis L. is one of the worst weeds of rice world-wide and has evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in rice fields of California. Propanil use was intensified to control the widespread resistant biotypes. Rice growers have recently experienced poor control, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to detect the presence of propanil resistance, to establish resistance levels, and to investigate involvement of enhanced herbicide detoxification as mechanism of resistance through the use of metabolic inhibitors. Four C. difformis populations collected in rice fields from the Sacramento Valley of California were confirmed resistant to propanil. This is the first case of such resistance outside the Poaceae and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl and malathion applied individually in mixture with propanil had minor effects on herbicide toxicity suggesting metabolic detoxification was not a resistance mechanism. A resistant biotype produced more than 80% biomass after a propanil (6.7 kg a.i. ha−1) and carbaryl (1.9 kg a.i. ha−1) or propanil and malathion (1.0 kg a.i. ha−1) treatment compared to

A toxin-deficient mutant strain, HP001 mutant of Alternaria alternata, whose mycelium is unable to infect its host, produces little tenuazonic acid (TeA) toxin. How TeA plays a role in initiating host infection by A. alternata remains unclear. In this research we use Imaging-PAM based on chlorophyll fluorescence parameters and transmission electron microscopy to explore the role of TeA toxin during the infection process of A. alternata. Photosystem II damage began even before wild type mycelium infected the leaves of its host, croftonweed (Ageratina adenophora). Compared with the wild type, HP001 mutant produces morphologically different colonies, hyphae with thinner cell walls, has higher reactive oxygen species (ROS) content and lower peroxidase activity, and fails to form appressoria on the host surface. Adding TeA toxin allows the mutant to partially recover these characters and more closely resemble the wild type. Additionally, we found that the mutant is able to elicit disease symptoms when its mycelium is placed on leaves whose epidermis has been manually removed, which indicates that TeA may be determinant in the fungus recognition of its plant host. Lack of TeA toxin appears responsible for the loss of pathogenicity of the HP001 mutant. As a key virulence factor, TeA toxin not only damages the host plant but also is involved in maintaining ROS content, host recognition, inducing appressoria to infect the host and for allowing completion of the infection process.

The greatest cost to the farmer in time and variable costs is control of weeds (Highly Invasive Vegetation = HIV). Despite farmer efforts, weeds still result in the greatest crop losses of all biotic constraints. The costs due to this HIV are greatest in the parts of the developing world where manual labor (more typically “femanual”) is used, and the populations are becoming more aged (due to youth abandoning agriculture), or more feeble due to debilitating diseases such as malaria and HIV-AIDS. Two case studies are presented: the previously intractable problems with Striga (witchweed) species in Africa; and rice cultivation and the emerging problems with the labor-saving shift to direct seeding, which has resulted in outbreaks of a weedy/feral form of rice, as well as herbicide-resistant Echinochloa spp. Biotechnology has much to offer as part of the solution to these major HIV problems, whether as transgenic herbicide resistant crops, or as weed resistant crops or through transgenically enhanced weed-specific biocontrol agents. Where necessary, transgenic tricks will also be needed in many cases to prevent transgene flow from crop to related weedy relatives, and possible technologies are described. Ever since the advent of agriculture, solutions to crop protection problems have been effective but ephemeral, and new solutions will be needed in the future. Using mixed solutions leads to solutions lasting synergistically longer, so efforts should be made to use mixed technologies to extend the lifetime of the next generation of sorely needed solutions to the problems of HIV.

Transgenic herbicide-resistant rice is needed to control weeds that have evolved herbicide resistance, as well as for the weedy (feral, red) rice problem, which has been exacerbated by shifting to direct seeding throughout the world-firstly in Europe and the Americas, and now in Asia, as well as in parts of Africa. Transplanting had been the major method of weedy rice control. Experience with imidazolinone-resistant rice shows that gene flow to weedy rice is rapid, negating the utility of the technology. Transgenic technologies are available that can contain herbicide resistance within the crop (cleistogamy, male sterility, targeting to chloroplast genome, etc.), but such technologies are leaky. Mitigation technologies tandemly couple (genetically link) the gene of choice (herbicide resistance) with mitigation genes that are neutral or good for the crop, but render hybrids with weedy rice and their offspring unfit to compete. Mitigation genes confer traits such as non-shattering, dwarfism, no secondary dormancy and herbicide sensitivity. It is proposed to use glyphosate and glufosinate resistances separately as genes of choice, and glufosinate, glyphosate and bentazone susceptibilities as mitigating genes, with a six-season rotation where each stage kills transgenic crop volunteers and transgenic crop x weed hybrids from the previous season.

Twenty-one grass weeds have evolved resistance to herbicides in Latin America, particularly in rice, soybean, wheat, and orchards. Junglerice, the most widespread and economically important rice weed, evolved resistance to propanil, acetyl-coenzyme A carboxylase (ACCase)-inhibitor herbicides, quinclorac, and imazapyr in Central America, Colombia, and Venezuela. Some junglerice populations are resistant to at least three herbicide modes of action. Other herbicide-resistant (HR) rice weeds are barnyardgrass and gulf cockspur to quinclorac in Brazil, and saramollagrass to ACCase-inhibitor herbicides in Colombia and bispyribac in Venezuela. Populations of weedy rice resistant to imidazolinones are now emerging, most likely originated from gene flow from imidazolinone-resistant rice. Saramollagrass also became resistant to nicosulfuron in corn in Venezuela. Eight species associated with soybean are resistant to ACCase-inhibitor herbicides in Brazil (alexandergrass, goosegrass, and southern crabgrass) and Boliv...

A combination of unique EPSPS structure and increased gene copy number and expression contribute to natural glyphosate tolerance in three lilyturf species. A few plants are naturally tolerant to glyphosate, the most widely used non-selective herbicide worldwide. Here, the basis for natural tolerance to glyphosate in three lilyturf species, Ophiopogon japonicus (OJ), Liriope spicata (LS), and Liriope platyphylla (LP), is characterized. These species tolerate glyphosate at about five times the commercially recommended field dose. They share three unique amino acids in their 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that affect glyphosate binding. These correspond to Asp71Met, Ala112Ile, and Val201Met amino acid variations compared to 231 other published plant EPSPS amino acid sequences. There was also a common deletion at 91 of a highly conserved glutamic acid. Glyphosate-treated lilyturf plants accumulated little shikimic acid but had significantly higher levels of EPSPS mRNA than initially expressed in the control. The IC50 of LsEPSPS was 14.0 µM compared to the 5.1 µM of Arabidopsis thaliana. The higher K m and K i values of LsEPSPS kinetics showed that LsEPSPS had lower substrate binding affinity to glyphosate. Overexpression of LsEPSPS in the recombinant E. coli BL21 (DE3) strain enhanced its tolerance to glyphosate. Both OJ and LS had two copies of the EPSPS gene, while LP had three copies. Therefore, a combination of unique EPSPS structure and increased gene copy number and expression contribute to natural glyphosate tolerance in the three lilyturf species.

Herbicide-resistant crops (HRCs), particularly glyphosate-resistant soybean, are increasingly important in Latin America. Prior to commercial release of these crops, their short- and long-term risks should be thoroughly assessed. A risk assessment should include the identification and characterization of potential hazards and an estimation of the likelihood of these hazards occurring. For HRCs the agro-ecological hazards are mostly related to the occurrence of herbicide-resistant (HR) weeds and crop volunteers and the adverse effects from the use of pesticides within the agricultural area. Herbicide-resistant rice is used as a case study to visualize the key components of such a risk assessment. For this purpose, a model that simulates a typical rain-fed rice production system in Central America was developed. The model was used to investigate the selection of HR weedy rice populations under various scenarios. Scenarios included contrasting weed management practices, hybridization levels between the comme...

Genetically modified, herbicide-resistant crop (HRC) cultivars, which allow for simplified weed control decisions compared with conventional cultivars, have considerable potential in Latin America. The number of herbicide applications can be reduced in HRCs, and otherwise difficult-to-control species, including red rice in rice or herbicide-resistant weeds, can potentially be managed. The American tropics include the centers of origin of several crops, such as corn and potato, and natural or agrestal floras containing wild near relatives of introduced crops, including rice and cotton, for which HRCs could be used. Potential direct impacts of HRC adoption on biodiversity in Latin America include changes in the genetic diversity of crops, increased volunteer crop problems, and invasion by resistant cultivars of natural areas beyond the farm boundary. Additionally, there is a risk associated with the escape of transgenes from HRCs, involving introgression to weedy relatives on a field scale leading to amplif...

Weedy rice infests paddy fields worldwide at an alarmingly increasing rate. There is substantial evidence indicating that many weedy rice forms originated from or are closely related to cultivated rice. There is suspicion that the outbreak of weedy rice in China may be related to widely grown hybrid rice due to its heterosis and the diversity of its progeny, but this notion remains unsupported by direct evidence. We screened weedy rice accessions by both genetic and molecular marker tests for the cytoplasmic male sterility (CMS) genes (Wild abortive, WA and Boro type, BT) most widely used in the production of indica and japonica three-line hybrid rice as a diagnostic trait of direct parenthood. Sixteen weedy rice accessions of the 358 tested (4.5%) contained the CMS-WA gene; none contained the CMS-BT gene. These 16 accessions represent weedy rices recently evolved from maternal hybrid rice derivatives, given the primarily maternal inheritance of this trait. Our results provide key direct evidence that hybrid rice can be involved in the evolution of some weedy rice accessions, but is not a primary factor in the recent outbreak of weedy rice in China.

Glyphosate is widely used in coffee plantations to control weeds. Lacking selectivity, glyphosate spray drift is suspected to cause adverse effects in coffee plants. Symptoms caused by glyphosate can be similar to those produced by other stress factors. However, shikimic acid accumulation should be a useful biomarker for glyphosate exposure as shown for other crops. The aim of this study was to assess the sensitivity of coffee plants towards glyphosate on different biological response variables and to evaluate the use of shikimic acid as biomarker. Dose-response experiments yielded ED50 values (50% effect dose) in the range of 38-550 ga.e.ha(-1) depending on the quantitative or qualitative variable monitored. The frequency of plants showing symptoms was the most sensitive variable. The best sampling time for shikimic acid accumulation was 1-2 weeks after glyphosate application, depending on experimental conditions. The highest shikimic acid accumulation was observed in young leaves. Shikimic acid is a suitable biomarker for a glyphosate exposure in coffee, using only young leaves for the analysis. Young coffee plants are susceptible to glyphosate damage. If symptoms are absent the risk of severe crop damage or yield loss is low.

Field experiments were conducted at four locations in the Central Pacific region of Costa Rica between 1994 and 1996 to determine suitable tactics for integrated control of propanil-resistant junglerice in rain-fed rice. Stubble incorporation within 3 mo after rice harvest did not affect the density of junglerice that emerged with the crop at the beginning of the rainy season at any location. However, the elimination with glyphosate of the first junglerice seedling population emerging before rice planting consistently reduced the in-crop infestation of junglerice and resulted in increased grain yields. The positive effect of eliminating the first junglerice flush remained even after the in-crop treatments were applied and lasted after rice harvest. Substitution of the two customary applications of propanil (3.8 kg ha−1 each) with a single application of pendimethalin (0.75 to 1.5 kg ha−1), preemergence or early postemergence, also reduced junglerice infestation and improved grain yield. Both prop...

Pre-emergence activity of pendimethalin on propanil-resistant jungle rice (Echinochloa colona) was demonstrated in glasshouse trials. Both susceptible and resistant populations, collected from Costa Rica, were controlled by 1.25 kg ha -1 , the usual application rate used in the field where Rottboellia cochinchinensis is also a problem. When applied post-emergence, propanil performance was improved by the addition of low doses of pendimethalin to the herbicide mixture. A propanil-resistant selection was controlled by 0.23 kg ha -1 pendimethalin + 0.54 kg ha -1 propanil at the one-to-two leaf stage, and 0.23 kg ha -1 pendimethalin + 1.08 kg propanil at the three-to-four leaf stage compared to 1.08 kg and 2.16 kg ha -1 respectively when propanil was applied alone. This suggests that pendimethalin improves post-emergence control in the field compared to the standard propanil treatment and can provide residual pre-emergence control of late-germinating individuals, so reducing the propanil selection pressure. For effective jungle rice control, growers apply propanil (3.84 kg ha -1 ) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop-P-ethyl (0.045 kg ha -1 ) at 35 DAP. Field experiments, conducted in dry-seeded upland rice in southern Costa Rica, demonstrated that under high jungle-rice population pressure, one application of pendimethalin at 1.5 kg ha -1 provided an effective replacement for propanil, resulting in reduced weed-control costs.

The effect of the mono-oxygenase inhibitors tridiphane, piperonyl butoxide and prochloraz on propanil uptake, metabolism and phytotoxicity was measured in a resistant (R) biotype of Echinochloa colona. The uptake of propanil was not significantly affected by any of the three mono-oxygenase inhibitors. The first metabolite of propanil metabolism, 3,4-dichloroaniline, was found to accumulate to higher levels in E. colona treated with each of the mono-oxygenase inhibitors mixed with formulated propanil, compared to propanil applied alone. Accumulation of further metabolites of propanil (glucosyl-3,4-dichloroaniline and bound products) was reduced in the presence of mono-oxygenase inhibitors, compared with propanil application alone. Leaf damage caused by a single drop of propanil compared to propanil + mono-oxygenase inhibitor was used to assess the degree of propanil tolerance in E. colona biotypes. Leaf damage was significantly greater in propanil + mono-oxygenase inhibitor treatments. No leaf damage was observed in mono-oxygenase inhibitor treatments alone at the concentrations used. Peroxidase activity was measured in crude extracts of the R-biotype of E. colona using 3,4-dichloroaniline as substrate, in the presence and absence of mono-oxygenase inhibitors and the specific peroxidase inhibitor salicylhydroxamic acid. Peroxidase activity was inhibited by all three mono-oxygenase inhibitors at 10 μM and by salicylhydroxamic acid at 1 μm. Glucosyl-3,4-dichloroaniline was found not to be a substrate for peroxidase activity. These results suggest that the incorporation of 3,4-dichloroaniline into bound residues involves peroxidase activity which can be inhibited by mono-oxygenase inhibitors. When peroxidase activity is inhibited, the precursor metabolite 3,4-dichloroaniline accumulates, and propanil resistance in E. colona is reduced, possibly as a consequence of phytotoxicity of this metabolite and/or product inhibition of the first step in propanil metabolism, responsible for the formation of 3,4-dichloroaniline. Glasshouse trials have demonstrated that the application of mono-oxygenase inhibitors, (particularly tridiphane which is also known to inhibit glutathione transferase activity) with propanil offers a promising approach to the control of propanil resistant biotypes of Jungle-Rice.

Uptake and metabolism of propanil were measured in both susceptible (S) and resistant (R) biotypes of Jungle-rice, Echinochloa colona (L.) link at different growth stages. Results showed that there was no significant difference in uptake between S and R biotypes of E. colona at any given growth stage, but that uptake was significantly reduced at older plant growth stages in all biotypes studied. Metabolism of propanil was more rapid in R biotypes than in S biotypes at all growth stages studied. Specific and total aryl acylamidase activity, responsible for the first stage of propanil metabolism, was higher in R biotypes than in S at all growth stages, but declined to about 50% of the maximum at older growth stages, confirming the importance of this enzyme in conferring resistance to this herbicide. The area of necrosis that developed around a single drop of propanil deposited on the adaxial leaf surface was used to assess the degree of propanil resistance; it was found that resistance increased at older E. colona growth stages in contrast to the rate of propanil metabolism and amidase activity. Treatment of leaves with the amidase inhibitors, carbaryl or piperophos, simultaneously with propanil, caused a decrease in resistance at growth stages where amidase activity was greatest. This treatment was less effective at older growth stages. These results show that, in E. colona, propanil metabolism is important for conferring resistance in younger plants (four-six-leaf stage). It is suggested that restricted uptake confers resistance in older plants

Aryl acylamidase (aryl-acylamine amidohydrolase, EC 3.5.1.13) activity has been measured in crude extracts from leaves of propanil-susceptible (S) and propanil-resistant (R) biotypes of the grass weed. Echinochloa colona (L.) Link from Columbia. Both specific and total amidase activity increased with plant age up to 15 days (four-leaf stage), then decreased beyond 20 days to about 50% of the maximum at 36 days in both R and S E. colona biotypes. Specific activity with propanil in the R biotype was about 80% of that obtained for rice (Oryza sativa L.), compared to 25% in the susceptible biotype. The specific activity of the propanil amidase was three-fold higher in the R biotype than in the S. Partially purified amidase extracts from rice and both S and R biotypes of E. colona were compared biochemically. Both rice and E. colona amidases had a pH optimum of 7.5 and native relative molecular masses, estimated by gel filtration, of 179 000 and 181 000, respectively. Out of six substrates tested, three produced appreciable activity (propanil, 4-chloroacetanilide and acetanilide) in both rice and E. colona. Michaelis constants showed that the rice amidase had a higher affinity for propanil (0.36 mM) than had the E. colona enzyme (1.1 mM). Carbamates and organo-phosphorus pesticides were shown to inhibit amidase activity in partially purified rice and E. colona extracts. Additional preliminary data have implicated peroxidase in the next step of propanil metabolism in vitro. These data demonstrate that increased aryl acylamidase activity contributes to resistance to the herbicide propanil in E. colona weeds. Also, a biochemical comparison of purified aryl acylamidases from S and R biotypes of E. colona is presented for the first time.

Primary root cells from five dinitroaniline-resistant (R) and three susceptible (S) goosegrass biotypes from North Carolina and South Carolina were observed by transmission electron microscopy to determine whether resistance was associated with changes in cell wall formation. Cell wall malformations were found in some cells from two of the R-biotypes and in one of the S-biotypes. Malformations consisted of partially deposited cell walls and the inclusion of cell wall material in the cytoplasm. Some of the affected cells also had abnormal, lobed nuclei and malformed mitochondria. There seems to be little or no correlation between dinitroaniline resistance and cell wall malformations.

LMX1 is a LIM-homeodomain (LIM-HD)-containing protein expressed selectively in insulin-producing beta-cell lines, and it it has been shown to activate insulin gene transcription. The human LMX1 gene was mapped by fluorescence in situ hybridization to chromosome region 1q22-q23, yet Church et al. (1994, Nat. Genet. 6: 98-105) identified two exon-trapping products from human chromosome 9 that were highly homologous to hamster LMX1. In the current study, we demonstrate tissue-specific expression of an LMX1 (now known as LMX1.1)-related gene, named LMX1.2. The chicken C-LMX1 gene, recently cloned using the hamster LMX1.1 sequence and shown to specify dorsal cell fate during vertebrate limb development (9), is actually more related to human LMX1.2 than LMX1.1. We have identified a unique simple sequence repeat polymorphic marker (hLMX1.2CA1) in a P1 genomic clone containing the human LMX1.2 gene and genetically mapped the marker on chromosome 9 between markers D9S1825 and D9S290 with odds of at least 1000:1. In addition, we localized the human LMX1.1 gene to three CEPH "B" yeast artificial chromosome clones (907A11, 935B12, and 947B2), along with two nearby polymorphic markers (D1S426 and D1S194)). Identification of this new LIM-HD-related gene may provide the opportunity to elucidate further the function of LIM class homeobox genes. Nearby polymorphic markers will be useful in testing the hypothesis that mutations in these LIM-HD genes result in genetic diseases such as non-insulin-dependent diabetes mellitus.

Dinitroaniline herbicides are absorbed readily by roots and emerging shoots, but shoot exposure is more phytotoxic. Translocation within the plant varies by specific herbicide but commonly is minor. Dinitroaniline herbicides injure plants by binding to tubulin, a dimer protein in the ceil that polymerizes to form microtubules (MTs). MTs form the major part of the mitotic apparatus, including spindle fibers, which enable chromosomes to separate during cell division. Dinitroaniline herbicides prevent tubulin from polymerizing into MTs, thus arresting mitosis. This leads to abnormal cells with more than the normal complement of chromosomes and, frequently, lobed nuclei. MTs also are responsible for orienting cell wall microfibrils in such a way that they prevent lateral enlargement of cells. Treatment with dinitroaniline herbicides leads to disorientation of the microfibrils, leading to one of the common symptoms—spherical cells instead of rectangular ones. Studies on the metabolism of trifluralin in plants have shown that amination, dealkylation, and cyclization all can occur. However, metabolites often amount to a small percentage of the original herbicide. In general, trifluralin seems quite stable within the plant.

Rapid detection methods were developed for discriminating between resistant (R) and susceptible (S) biotypes of Echinochloa colona to either propanil or fenoxaprop-P at all growth stages. In the pregerminated seed assay for fenoxaprop-P, seeds were placed on 1.0% agar containing a range of concentrations of herbicides and kept under humid conditions. For propanil, pregerminated seeds were placed on moist filter paper in the lid of a petri dish and, when one leaf had developed, the lid was inverted for 1 min into propanil solutions at a range of concentrations. For the fenoxaprop-P and propanil test, seedling length and fresh weight were measured after 1 wk. For juvenile plants with four-leaf to one-tiller, shoots and roots were trimmed and placed in 20-ml glass tubes containing 0.2% (wt/v) agar and a range of concentrations of herbicides. Shoot extension and weight were recorded after 7 d. Larger plants with several small tillers were also assayed by this method. Tillers were removed from larger ...

Listeria monocytogenes is a bacterial pathogen causing severe food-borne infections in humans and animals. It can sense and adapt to a variety of harsh microenvironments outside as well as inside the host. Once ingested by a mammalian host, the bacterial pathogen reaches the intestinal lumen, where it encounters bile salts which, in addition to their role in digestion, have antimicrobial activity. Comparison of the L. monocytogenes and Listeria innocua genomes has revealed the presence of an L. monocytogenes-specific putative gene encoding a bile salt hydrolase (BSH). Here, we show that the bsh gene encodes a functional intracellular enzyme in all pathogenic Listeria species. The bsh gene is positively regulated by PrfA, the transcriptional activator of known L. monocytogenes virulence genes. Moreover, BSH activity increases at low oxygen concentration. Deletion of bsh results in decreased resistance to bile in vitro, reduced bacterial faecal carriage after oral infection of the guinea-pigs, reduced virulence and liver colonization after intravenous inoculation of mice. Taken together, these results demonstrate that BSH is a novel PrfA-regulated L. monocytogenes virulence factor involved in the intestinal and hepatic phases of listeriosis.