Qualitative/quantitative strategy for the determination of glufosinate and metabolites in plants.

A simple method for the simultaneous determination of glufosinate and itsmetabolites in plants based on liquid chromatography­ultraviolet (LC­UV) absorption detection after derivatization with fluorenylmethoxycarbonyl chloride (FMOC-Cl) of some analytes to facilitate separation is reported here. Nonavailable standard metabolites were identified by LC­TOF/mass spectrometry (MS), which also confirmed all target analytes. Ultrasound-assisted extraction was used for sample preparation (power of 70 Wand duty cycle of 0.7 s/s for 10 min) with subsequent evaporation of the extractant, reconstitution and filtration as the cleanup/concentration step prior to derivatization, and chromatographic separation and detection at 270 nm for underivatized analytes and 340 nm for those that were derivatized. The chromatographic analysis was completed in 40 min using a Luna® column (C18 phase). The analytical characteristics of the method were linear dynamic range of the calibration curves within 0.047­700 µg/mL with a regression coefficient (rc) of 0.999 for glufosinate, 0.077­700 µg/mL with a rc of 0.998 for N-acetyl-glufosinate, and 0.116­600 µg/mL with a rc of 0.998 for 3-(methylphosphinico)propanoic acid. The precision for the determination of glufosinate (studied at two levels, 0.1 and 5 µg/mL) was 2.7 and 6.0 % for repeatability and 4.7 and 7.2%for within-laboratory reproducibility, respectively. Identification and confirmatory analysis of the presence of glufosinate and metabolites in the extracts from treated plants was carried out by LC­TOF/MS in high-resolution mode for the precursor ion. The method was validated by analyzing wheat (Triticum aestivum) samples (resistant and susceptible biotypes) treated with 300 g of glufosinate/ha following conventional agronomical practices.

Qualitative/quantitative strategy for the determination of glufosinate and metabolites in plants.

A simple method for the simultaneous determination of glufosinate and its metabolites in plants based on liquid chromatography-ultraviolet (LC-UV) absorption detection after derivatization with fluorenylmethoxycarbonyl chloride (FMOC-Cl) of some analytes to facilitate separation is reported here. Nonavailable standard metabolites were identified by LC-TOF/mass spectrometry (MS), which also confirmed all target analytes. Ultrasound-assisted extraction was used for sample preparation (power of 70 W and duty cycle of 0.7 s/s for 10 min) with subsequent evaporation of the extractant, reconstitution and filtration as the cleanup/concentration step prior to derivatization, and chromatographic separation and detection at 270 nm for underivatized analytes and 340 nm for those that were derivatized. The chromatographic analysis was completed in 40 min using a Luna® column (C18 phase). The analytical characteristics of the method were linear dynamic range of the calibration curves within 0.047-700 µg/mL with a regression coefficient (rc) of 0.999 for glufosinate, 0.077-700 µg/mL with a rc of 0.998 for N-acetyl-glufosinate, and 0.116-600 µg/mL with a rc of 0.998 for 3-(methylphosphinico)propanoic acid. The precision for the determination of glufosinate (studied at two levels, 0.1 and 5 µg/mL) was 2.7 and 6.0 % for repeatability and 4.7 and 7.2 % for within-laboratory reproducibility, respectively. Identification and confirmatory analysis of the presence of glufosinate and metabolites in the extracts from treated plants was carried out by LC-TOF/MS in high-resolution mode for the precursor ion. The method was validated by analyzing wheat (Triticum aestivum) samples (resistant and susceptible biotypes) treated with 300 g of glufosinate/ha following conventional agronomical practices.

Leaching of oxadyxil and tebuconazole in Colombian soil.

Lake Tota (Boyaca, Colombia) supplies water for human consumption, agriculture and industry for more than 500.000 people. Oxadixyl and Tebuconazole are fungicides used in onion crops in the lake catchment area. The mobility of pesticides in soil, bioavailability and transfer to other environmental compartments depend on sorption and desorption kinetics and mechanisms. An understanding of these processes is essential for transport modeling and the rational design of corrective measures against pollution. A displacement study was performed on a hand packed soil column in laboratory conditions. A pulse of 0,01 M CaCl2 solution, containing a tracer (Bromide) and the fungicides Oxadixyl y Tebuconazole, was injected. Column experiment was performed at 0.078 cmh(-1) flow rate under unsaturated conditions. Eluates were collected in flasks at constant intervals and the volumes of eluate were recorded. After rainfall simulation, the soil from the column was sliced into six successive sections (5 cm). Methanol extraction was used to determine the fungicide in each soil section. Samples were measured by HPLC. Only Oxadixyl was recovered in leachates. Unlike bromide breakthrough curve, Oxadixyl was asymmetrical, with early breakthrough and increased tailing. The percentage eluted was 96.7% after ten pore volumes. Tebuconazole showed the highest retention in the first five cm of soil layer. The results suggest that oxadyxil presents highs risk to leachate through the soil profile and that Tebuconazole is strongly absorbed in Colombian soil.

Screening and confirmatory analysis of glyoxylate: a biomarker of plants resistance against herbicides.

The evidence that glyoxylate is a biomarker of tolerance or susceptibility to the action of herbicides belonging to the glycine family makes necessary to develop simple methods for the determination of this metabolite. Glyoxylate level allows both to know the presence/absence of members of the glycine family in plants and plant response to these herbicides. With this aim, a colorimetric-screening method has been developed for determination of glyoxylate based on formation of a phenylhydrazone, then oxidised to red coloured 1,5-diphenylformazan. Simultaneous optimization of ultrasound-assisted extraction of glyoxylate from plants and derivatization by a multivariate design has allowed the determination of the target analyte in fresh plants without interferences from pheophytines and compounds with carbonyl groups. Limits of detection and quantification are 0.05 µg ml(-1) and 0.17 µg ml(-1), respectively, with precision, expressed as relative standard deviation, of 3.3% for repeatability and 5.6% for the within-day laboratory reproducibility. Only 50mg of plant is necessary for determination of glyoxylate within 32 min. Confirmatory analysis by capillary electrophoresis-diode array detection in samples of Lolium spp. subjected to treatment with glyphosate shows that the relative error of the proposed method is always lower than 7%.

Late watergrass (Echinochloa phyllopogon): mechanisms involved in the resistance to fenoxaprop-p-ethyl.

Fenoxaprop-p-ethyl (FE), 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate, ethyl ester (R), is an aryloxyphenoxypropionate herbicide for postemergence control of annual and perennial grasses in paddy fields; its site of action is acetyl-coenzyme A carboxylase (ACCase), an enzyme in fatty acids biosynthesis. The possible mechanism(s) of resistance to FE in a resistant biotype of Echinochloa phyllopogon was examined, namely, absorption, translocation, and metabolism of FE and ACCase susceptibility to fenoxaprop acid (FA). Studies of the in vitro inhibition of ACCase discounted any differential active site sensitivity as the basis of resistance to FE. There were differences in absorption rates between biotypes from 3 to 48 h after application (HAA). Biotypes did not differ in either the amounts or the rates of FE translocated; 98% of applied [14C]FE remaining in the treated leaf. However, there was a good correlation between the rate of herbicide metabolism and the plant resistance. The R biotype produced 5-fold less FA and approximately 2-fold more nontoxic (polar) metabolites 48 HAA than the S biotype. Moreover, the higher rate of GSH conjugation in the resistant biotype as compared to the susceptible one indicates that GSH and cysteine conjugation is the major mechanism of resistance of the R biotype against FE toxicity.

DNA topoisomerase I from parasitic protozoa: a potential target for chemotherapy.

The growing occurrence of drug resistant strains of unicellular prokaryotic parasites, along with insecticide-resistant vectors, are the factors contributing to the increased prevalence of tropical diseases in underdeveloped and developing countries, where they are endemic. Malaria, cryptosporidiosis, African and American trypanosomiasis and leishmaniasis threaten human beings, both for the high mortality rates involved and the economic loss resulting from morbidity. Due to the fact that effective immunoprophylaxis is not available at present; preventive sanitary measures and pharmacological approaches are the only sources to control the undesirable effects of such diseases. Current anti-parasitic chemotherapy is expensive, has undesirable side effects or, in many patients, is only marginally effective. Under this point of view molecular biology techniques and drug discovery must walk together in order to find new targets for chemotherapy intervention. The identification of DNA topoisomerases as a promising drug target is based on the clinical success of camptothecin derivatives as anticancer agents. The recent detection of substantial differences between trypanosome and leishmania DNA topoisomerase IB with respect to their homologues in mammals has provided a new lead in the study of the structural determinants that can be effectively targeted. The present report is an up to date review of the new findings on type IB DNA topoisomerase in unicellular parasites and the role of these enzymes as targets for therapeutic agents.

Morphological and molecular characterization of different Echinochloa spp. and Oryza sativa populations.

Echinochloa P. Beauv. is an important genus because many of its species are weeds infesting most paddy fields, which can reduce the rice grain production by up to 80%. A controversy exists about the taxonomy of the genus due to the high level of morphological variations found in these species. Cyhalofop-butyl, an aryloxyphenoxy-propionate herbicide, is used to control Echinochloa spp. in paddy fields, although differences in susceptibility were found between different Echinochloa species. E. colona was highly susceptible [ED50= 34 g of active ingredient (ai) ha(-1)]; very similar results were obtained with the remaining species. By contrast, E. oryzicola (170 g of ai ha(-1)) was less sensitive, with the herbicide symptoms appearing later. Because of this differential susceptibility, morphological and molecular studies were carried out. A morphological study, using 21 characters both quantitative and qualitative of spikelets and seedlings, was capable of clearly distinguishing closely related E. crus-galli plants (two populations), E. muricata and E. crus-pavonis, and E. oryzicola, E. utilis, and E. colona species. The resolution of Echinochloa species at the molecular level, based on RAPD analyses, was fairly consistent with morphological analysis results. Among the 60 primers screened, 21 primers exhibited polymorphic bands and produced a total of 136 RAPD markers. Of all the amplified fragments, 90 were found to be polymorphic. E. oryzicola and E. colona were clearly separated, and the RAPD analyses showed that both E. crus-galli populations were 100% related and 51% related to E. utilis, whereas E. crus-pavonis and E. muricata (73% similarity) appeared as being clearly separated from this group.

Effects of the foliar-applied protein "Harpin(Ea)" (messenger) on tomatoes infected with Phytophthora infestans.

The active ingredient in Messenger, is Harpin(Ea), a naturally occurring protein derived from Erwinia amylovora, a causal agent of fire blight. When Messenger is applied to a plant, the protein Harpin(Ea) binds foliar receptors to it. The receptors recognize the presence of Harpin(Ea), sending a signal that a pathogen is present, actually "tricking" the plant into thinking that it is under attack. This binding process triggers a cascade of responses affecting a global change of gene expressions, stimulating several distinct biochemical pathways within the plant responsible for growth and disease and insect resistance. The objective of this work is to characterize the development of an induced resistance against Phytophthora infestans. No effective treatment is currently available against this pathogenic agent, which causes the loss of complete harvests of different crops. Tomato plants with and without Messenger applications were inoculated with Phytophthora infestans in the same way. In addition, some plants with and without Messenger applications were not inoculated. Inoculated plants were symptomatologically checked for local and systemic symptoms. Evaluations of the number of tomatoes produced, with or without damage, and their growth, were also carried out. Based on the data obtained from the assays, significant changes were observed in the parameters measured due to Messenger treatment. The severe damage of this disease was reduced in the plants which received Messenger applications. These results open up new pathways in the control of diseases like Phytophthora infestans, in which effective means to combat them still do not exist, or these means are harmful to the environment.

Induction of resistance to the pathogenic agent Botrytis cinerea in the cultivation of the tomato by means of the application of the protein "Harpin"(Messenger).

Harpin(Ea), an active component in Messenger, was originally isolated from the bacterial plant pathogen Erwinia amylovora based on its ability to elicit a hypersensitive response (HR). This bacterial pathogen causes "fire blight", a disease in apples and other members of the Rosaceae. Harpin(Ea) also induces resistance in a variety of plants against a wide array of pathogens. The objective of this investigation was to determine indications of resistance induction to Botrytis cinerea in the plants treated with the formulated Harpin(Ea) protein. This pathogenic agent is responsible for important economic losses in the cultivation of both greenhouse and field grown tomatoes. Plants with and without Messenger applications were inoculated with Botrytis cinerea in the same way. In addition, some plants with and without Messenger applications were not inoculated. Inoculated plants were symptomatologically checked for local and systemic symptoms. Evaluations of the number of tomatoes produced and their growth were also carried out. The results obtained demonstrate that there were active defence systems in the plant, producing a reduction in the damage caused by the pathogenic agent Botrytis cinerea. A greater growth also took place in the fruit obtained. These results show that the formulated Harpin(Ea) protein could reduce the use of chemical agents and be a new tool to serve as the basis for an Integrated Pest Management system.

Glyphosate resistance in a Chilean Lolium multiflorum.

Lolium multiflorum (Italian ryegrass) has recently demonstrated itself to be poorly controlled with glyphosate in cereal crops of South Chile. The concentration of glyphosate necessary to reduce shoot length by 50% (ED50) in seedlings, after eight days of root contact was 7.3-fold in the resistant Vil-1 than in the susceptible (S) biotype. The obtained spray retention values were higher on S than the resistant (Vil-1) biotype. Contact angles measured on the adaxial surface of S and Vil-1 were similar. However, on the abaxial surface contact angles were of 63 degrees on Vil-1 as compared to 42 degrees on S. A greater glyphosate uptake was observed through the abaxial surface of S. Regarding translocation, glyphosate accumulated mainly in the tip of the treated leaf of Vil-1, 24 h after treatment. It was afterwards also well distributed to the rest of the leaves and roots, as in the susceptible biotype. Nevertheless, 14C-glyphosate remained higher in the foliar apex of Vil-1. Hence, resistance to glyphosate by the Vil-1 Lolium multflorum biotype seems to involve a lower uptake through the abaxial leaf surface and a different migration pattern.

Evaluation of resistance in Cyperus difformis populations to ALS inhibiting herbicides.

Due to the intensification of rice cultivation in Spain and the repeated use of herbicides as an effective tool to control weeds, one important fact is the appearance of resistant populations of weeds, which are no longer controlled effectively at field doses. Therefore, it is necessary to increase doses to such an extent as to produce phytotoxicity in the rice crop. In paddy fields in Badajoz (Spain), a few years ago, populations of Cyperus difformis resistant to bensulfuron-methyl appeared. In order to characterize this resistance, whole plant assays were carried out in fourteen populations, eight of them originating from treated Spanish paddy fields. The results were expressed as resistance factor (RF) = ED50(R)/ED50(S). Two populations of Cyperus difformis, resistant (R) and tolerant (T) to bensulfuron-methyl, displayed resistance factors greater than 30 and 12.5, respectively. Furthermore, in order to evaluate the existence of a possible cross-resistance, the recommended field doses of 3 other herbicides (imazamox, ethoxysulfuron and bentazone + MCPA) were applied to the plants. All populations were susceptible to both imazamox and bentazone + MCPA and two populations showed cross-resistance to ethoxysulfuron. ALS activity was assayed in vitro in four biotypes, the R/S ratios of the I50 values calculated indicate that resistance involves a reduction in the sensitivity of the ALS mainly in the R population (biotype 4) to bensulfuron-methyl and ethoxysulfuron, displaying R/S ratios of 37500 and 142857, respectively, which may be attributed to inherent differences in the ALS protein itself and/or in the stability of the enzyme.

Cross resistance to accase herbicide in Lolium rigidum.

Lolium rigidum is a cross-pollinating grass weed present in Europe and occurring in winter wheat and orchard crops. Several graminicides such as chlorotoluron and/or isoproturon and diclofop-methyl in mixtures or alone have been used successfully to control this weed in Spain during the past decade. However, several L rigidum populations have developed resistance to these herbicides following selection due to their continuous use. Four resistance mechanisms have been found in this grass weed, an enhanced metabolic detoxiflcation of the herbicides and an insensitive isoform of ACCase being the most important ones. The extent of cross-resistance depends on the type of mechanism. The biotype with an enhanced metabolic detoxification showed cross-resistance to ACCase-, ALS-, PSII- and tubuline-inhibiting herbicides, while the biotype resistant due to a mutation of the target site (ACCase) presented cross-resistance to ACCase-inhibiting herbicides only.

Weed control and persistence of two oxyfluorfen formulations in olive groves under non tillage conditions.

To obtain profitable yields in olive groves, residual preemergence herbicides are applied in October or November before the winter rains, and before the winter annual weeds germinate. Simazine, one of the herbicides most used for weed control in olive groves, has recently been banned. Oxyfluorfen is presented as a good alternative to simazine in olive fields. Experiments were carried out in 2002 and 2003 to evaluate the behaviour of two oxyfluorfen formulations, 2XL and G4F, at 480 g a.i. ha(-1) for three different soil management systems with three replications (1. bare soil; 2. bare soil and grassed buffer strips, chemically controlled and 3. bare soil and grassed buffer strips with controlled mowing; under non tillage conditions in all three cases). The most important species that survived 2XL and G4F treatments was Sagina apetala ARD. Oxyfluorfen residues were evaluated throughout 158 days after the applications. Three soil samples from each plot were collected, mixed and air dried. The herbicide extractions were made with methanol and the residues were analyzed by HPLC. We found no differences between the two formulations, but results showed that recoveries of oxyfluorfen were higher in plots with chemically controlled buffer grassed strips than in the other soil management types.

Evaluation of resistance in Amaranthus quitensis Kunth populations to imazethapyr and other imidazolinones.

Six populations of Amaranthus quitensis (R1, R3-R7), taken from soybean fields in Córdoba (Argentina), continuously treated with imazethapyr escaped from control with this herbicide. In order to characterize this resistance, whole plant assays were carried out using imazethapyr. Treatments were made at different doses, from 0.5 g a.i.ha(-1) to 60 g a.i.ha(-1), at 200 1 ha(-1) and 200 kPa pressure. Shoot fresh weight was mesured 21 days after treatment. The results were expressed as resistance factor (ED50(R)/ED50(S)). Different degrees of resistance were found as its shown by the respective resistance factors: R1:22.5, R3:6.5, R4:43.1, R5:8.6, R6:4, R7:5. Due to the high variability in the response to imazethapyr treatments shown in some populations, and according to previous investigations on the ALS gene that proved heterozygosity a screening was made, at the recommended dose of imazethapyr. Plants were classified according to their state, dead, alive and affected (fallen but alive). Populations 3, 6 and 7 showed an important heterozygosity. Furthermore, in order to evaluate the existance of a possible cross-resistance, the recommended doses of 4 other imidazolinones (imazametabenz, imazapyr, imazamox, imazaquin) were applied to the plants. All populations were susceptible to both imazamox and imazapyr and showed cross-resistance to imazamethabenz and imazaquin.

Is it possible to detect Echinochloa spp. tolerance to ACCase-inhibiting herbicides using a simple quick tolerance test?

The objective of this work was to evaluate the reliability of one quick tolerance test that would enable us, in only six days, to quantify tolerance levels of one biotype to one or more herbicides. For this purpose, we evaluated tolerance levels to cyhalofop-butyl of five Echinochloa spp. biotypes: muricata, crus-galli, crus-pavonis, oryzicola and utilis, with unknown records of herbicide treatment. Moreover, two biotypes of Echinochloa phyllopogon were tested, one of them resistant (R) to fenoxaprop-P-ethyl and the other one susceptible (S). The Oryza sativa Puntal var. and Oryza sativa var. (wild rice) were also checked in order to demonstrate cyhalofop-butyl selectivity profiles. The assays were conducted with petri-dishes where, over the following increasing doses, fifty seeds per biotype and dose, were placed in each one: 0, 3, 6, 12, 18, 24, 48 and 60 ppm of cyhalofop-butyl and codacide oil adjuvant. Six days later, the following parameters were evaluated: plumule length, root length, germination (%) and fresh weight reduction (%). E. muricata germination was reduced by 50% with a 6 ppm dose. A non linear relation dose-germination was observed in the rest of the biotypes. The plumule length permitted the ranking of the biotypes into three groups: (1) resistant (E. phyllopogon R) or very tolerant (Oryza sativa Puntal var. and wild rice), those with a reduction of less than 30%, (2) tolerant, between 30 and 60% (E. oryzicola), and (3) susceptible, with a reduction of over 80% (E. muricata, E. crus-galli, E. crus-pavonis, E. utilis and E. phyllopogon S). Only Oryzo sativa and E. phyllopogon R had a minimal reduction of fresh weight (less than 15%). The assays were repeated with whole plants and we checked the accuracy of this test that indicated the resistance level of one biotype in a quick, reliable and economic way.

Cross resistance to ALS-inhibiting herbicides in Euphorbia heterophylla L. biotypes resistant to imazethapyr.

The effect of weeds on the diminution of agricultural production is considered to be between 30 and 50%. Imazethapyr is a herbicide which acts on the enzyme ALS, the first common enzyme in the biosynthetic pathway of valine, leucine and isoleucine. Euphorbia heterophylla is a common species in soybean fields in Brazil and different populations resistant to herbicides of the sulfonylurea and imidazolinone groups are currently being reported. The objectives of this work were: to determine the resistance of three different biotypes named RI, RII and RII to the herbicide imazethapyr: to establish the level of resistance to this herbicide, and to evaluate the behaviour of the biotypes to other herbicides with a similar mode of action. The response of plants treated with imazethapyr confirmed the existence of resistance in the biotypes denominated as RI, RII and RIII. The imazethapyr concentration required to reduce the activity of the enzyme ALS by 50% (I50) should be greater than 500 microM for biotypes RI, RII and RIII and 39.47 microM for the susceptible biotype. Applications made in the greenhouse at field doses of ALS inhibiting herbicides showed cross resistance in the case of imazamox and imazamethabenz but not in the cases of the other ALS inhibitor herbicides used. ALS activity results demonstrated that the imazethaphyr resistance in different biotypes of E. heterophylla is target site mediated.

Biotypes resistant to herbicides in paddy fields in the Iberian Peninsula.

A consequence of modern agriculture and its dependence on herbicides, is the appearance of resistant weed populations. The first case of resistance on the Iberian Peninsula was found in Portugal and it was in a population of Alisma plantago-aquatica, resistant to bensulfuronmethyl, an ALS-inhibitor. For the same herbicide, control problems with Cyperus difformis were found in some Spanish rice fields. In the same rice field area, tolerance was observed in some Echinochloa spp. when auxinic herbicides (quinclorac) were used and some resistant Echinochloa spp. populations were found due to the long use of PS II inhibitors herbicides (propanil). The association of active ingredients, rotation of crops and adoption of mechanical control methods are the main strategies to combat resistance to herbicides.

Cross-resistance to ACCase inhibitors of Lolium multiflorum, Lolium perenne and Lolium rigidum found in Chile.

APPs (aryloxyphenoxypropionates) and CHDs (cyclohexanediones) are two of the most important groups used post-emergence for the control of grass weeds. They inhibit the lipid synthesis in plants by interfering with the activity of the enzyme Acetyl-coenzyme A carboxylase (ACCase), acting at a meristematic level. The resistance patterns of the biotypes characterized seem to indicate the existence of different degrees of resistance. It is thus possible to identify biotypes presenting cross-resistance only to certain APPs, to APPs and CHDs, or only to CHDs. The objective of this work was to evaluate the cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, propaquizafop, cyhalofop-butyl, haloxyfop-R-methyl, tralkoxydim and tepraloxydim in three species of Lolium (L. multiflorum, L. perenne, and L. rigidum) resistant to diclofop-methyl. The assays were conducted with petri-dishes in which, over increasing doses, fifty seeds per biotype and dose were located in each dish. Two weeks later, the following parameters were evaluated: germination (%), number of roots, radicle length, plumule length, and fresh weight reduction (%). Based on plumule length and fresh weight reduction (%), diclofop-methyl resistant biotypes showed cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, cyhalofop-butyl, haloxyfop-R-methyl, but not to propaquizafop, tralkoxydim and tepraloxydim. The parameters germination (%), number of roots or root length did not show a good relation between the dose and its efficacy (curves of dose response) for any of the susceptible and resistant biotypes studied.

Alternative control of two biotypes of Echinochloa phyllopogon susceptible and resistant to fenoxaprop-ethyl.

Rice (Oryza sativa var.), is one of the most important crops worldwide, and is cultivated in the five continents since it adapts itself to all climatic conditions. The most important weeds that reduce the world rice yield are Echinochloa spp., annual gramineae, which, because of the selection pressure imposed on them, have developed resistance to a large series of herbicides. Two Echinochloa phyllopogon biotypes were studied, one of them resistant to molinate, thiobencarb and fenoxaprop-ethyl and the other one susceptible to these herbicides, both originating from California rice fields. In these biotypes, the effects of other herbicides were evaluated, some of them with the same mode of action [profoxydim (Aura) and cyhalofopbutyl (Clincher), both ACCase inhibitors] and others with different modes of action [quinclorac (Facet) belonging to auxinic herbicide families; bispyribac-Na (Nominee) and azimsulfuron (Gulliver), both ALS inhibitors]. The only herbicide that effectively controlled the R biotype was profoxydim (95% control). Cyhalofop-butyl, quinclorac and bispyribac-Na did not control the R biotype by more than 40%. There is no doubt that azimsulfuron hardly had any effect (14%). On the other hand, in the S biotype, three herbicides were quite effective: profoxydim (93%), quinclorac (93%), and cyhalofop-butyl (90%). Bispyribac-Na and azimsulfuron hardly had any effect on the S biotype, with no significant differences in either herbicide (20%).