Biochemical and Molecular Knowledge about Developing Herbicide-Resistant Weeds

Herbicide resistance is the genetic capacity of a weed population to survive an herbicide treatment that, under normal use conditions, would effectively control the resistant weed population. Weeds have been evolving in conventional crop cultivars worldwide from selection pressure placed on them from repeated use of herbicides. In this chapter, we intend to explain the biochemical and molecular basis of herbicide resistance in weeds. On the other hand, herbicide resistance can be a useful tool so that weed scientists can use as important approach to control and manage weeds. There are several strategies for the production of HR crops by genetic engineering and the methods used in this process will be discussed in this chapter

Joint Action of Herbicides on Weeds and Their Risk Assessment on Earthworm (<em>Eisenia fetida</em> L.)

Frequent and intensive use of similar modes of action herbicides increases selection pressure resulting in nature adapt and a number of herbicide-resistant weeds. The most effective methods to prevent and delay herbicide-resistant weeds are herbicide tank mixture and adjuvant mixed herbicides. This chapter intends to explain the advantages of herbicide tank mixture and adjuvant mixed herbicides. In addition, the models of estimated herbicide mixture interaction response have been explained. Although herbicide mixtures have benefits, they may present risks leading to soil pollution and affecting soil fauna such as earthworms. Therefore, we discussed the negative effect of mixture herbicides on Eisenia fetida. On the other hand, various models to calculate mixture herbicide toxicity on earthworms will be present in this chapter

Clodinafop-Propargyl Resistance Genes in Lolium rigidum Guad. Populations Are Associated with Fitness Costs

Amino acid substitutions that confer herbicide-resistance may cause fitness costs in mutant plants at unfavorable levels in contrast to wild-species. The fitness costs in three Lolium rigidum populations (AH3 (Ile-2041-Asn) and BO2 (Ile-1781-Leu) as resistant (R) to clodinafop-propargyl, an ACCase (acetyl-CoAcarboxylase) inhibitor, carrying the mutations 1781 and 2041, respectively, and HF as susceptible (S)) were studied during 2014 and 2016. The germination rates and percentages of the three L. rigidum populations, and competition between them and Triticum aestivum using substitution series experiments were assessed. The BO2 and AH3 populations showed resistance to clodinafop-propargyl due to mutations in their ACCase genes. The germination rate for L. rigidum decreased as the sowing depth increased, with the lowest germination rate being found at 8 cm. AH3 and HF populations presented higher seed germination under water and NaCl salinity stress, but no fitness cost variations were observed among these R populations under optimal growth conditions. Diverse germination responses to light conditions were observed between the S and R L. rigidum populations. The highest germination percentage was observed in the HF population at the two-week lighting + two-week darkness regime. The comparison of relative yield total and relative crowding coefficient showed that T. aestivum was more competitive than L. rigidum. However, among ACCase-resistant L. rigidum populations, AH3 population was the most competitive presenting no fitness costs. This R population was more competitive than the S (HF) one under competitive conditions. These results show that fitness costs in the R L. rigidum populations vary according to the specific mutation at the ACCase gene that confers resistance to clodinafop-propargyl. In conclusion, mutations occurring at the 2041 position in the ACCase gene caused fitness costs, but those occurring at the 1781 position did not generate fitness costs for L. rigidum. Therefore, non-chemical methods should be considered unfavorable for resistant populations of this species

Effect of some adjuvants application on enhancing sulfosulfuron herbicide performance on Phalaris minor- Poaceae

Nowadays environmental pollution by pesticides application is a major concern for health. Efficiency of many herbicides can be increased by adding adjuvants to the spray solution. Therefore greenhouse study was conducted during 2014 to determine the efficacy of three adjuvants (Citogate, Castor oil and Canola oil) at concentrations of 0.1 and 0.2 (%v/v) with 5, 10, 20, 30 and 40 g a.i\ha of sulfosulfuron herbicide on littleseed canary grass. Results showed that the adjuvants enhanced the efficacy of sulfosulfuron in decreasing the dry weights of littleseed canary grass. Performance of herbicide was increased with enhancing its concentrations. Measured ED50 and ED90 concentrations of sulfosulfuron in control were 16.74 and 32.22 g a.i\ha, respectively. Whereas the values for Citogate 0.2 (%v\v), was 5.86 and 13.34 g a.i\ha, respectively. The addition of Citogate and Castor oil had the highest and lowest effect on sulfosulfuron efficacy against Littleseed canary grass. In conclusion, the study revealed that Citogate concentrations had powerful effects on herbicide efficacy followed by Canola oil

The Effect of Organic Mulches and Metribuzin on Weed Control and Yield of Tomato (Lycopersicon esculentum Mill.)

To evaluate the effects of four kinds of organic non-living mulches (wheat straw, sawdust, coco peat and peat moss) and metribuzin (herbicide treatment) on weed control and yield of tomato cv. "CH" an experiment was designed in randomized complete blocks with 7 treatments and 3 replications at the College of Agriculture, Shiraz University in 2012. According to the results all mulch treatments showed lower efficiency in weed control than the metribuzin. Also, all mulch treatments showed higher weed density compared to metribuzin. When straw, among non-living organic mulches, showed lowest weed control (62.3 weed.m-2). According to the results the highest tomato yield per unit area was produced by using peat moss mulch (from 5.7 kg.m-2) and the lowest yield from weedy plots (1.2 kg/m-2). To calculate the percentage of predicted performance of each of the treatments, only Gompertz model was applied and only the beginning of weed interference between the treatments was taken into account

Assessing the Effect of Prometryn Soil Residue on Soil Microbial Biomass and Different Crops using Bioassay Test

Introduction: Herbicides are the most widely used of chemical pesticides for agricultural production and landscape management. The environmental risk of herbicides should be evaluated near sites of application, even though basic ecotoxicological tests have been conducted before they can be registered for marketing. For example, triazine herbicides, which are photosynthetic PSII herbicide that considered only slightly or moderately toxic to many susceptible plants, soil microorganisms, mammals and humans, however, concerns have arisen because this herbicide are members of a class claimed to be carcinogenic, or may affect the development as reproductive toxins. For this reason, most reliable evidence is needed to test these claims and investigate their ecological effects. Prometryn is a herbicide belongs to triazine family that may leave residual activity in the soil for extended periods, causing injury and yield reduction of susceptible soil microorganisms and crops in rotation. Compared with other methods, the rapidity of response, sensitivity, high level of precision, simple process and easy operation are the advantages of bioassay methods for the routine monitoring of biologically available photosynthesis-inhibiting herbicides present in agricultural soils. Materials and Methods: A pot experiment was conducted under greenhouse conditions in order to study the sensitivity of 4 different crops to prometryn soil residue at the College of Agricultural Sciences, Ilam University, Ilam, Iran in 2014. Experimental type was completely randomized design in a factorial arrangement with three replications. Treatments included 4 different crops (lettuce, barley, rapeseed and beet) and prometryn simulated concentrations residues in soil (0.0033, 0.0166, 0.033, 0.066, 0.1 and 0.166 mg. kg-1soil). 15 cm diameter pots were filled with a modified soil and 10 of seeds of crops were planted in 5 regular positions. The plants were thinned to five plants per pot after germination. The pots were kept for 30 days under controlled conditions. Shoot and root biomass production was measured 30 days after emergence. At harvest, growth parameters including the dry weight of shoots and roots were determined. The data were subjected to analysis of variance by computer facilities, using Mstatc software. Plant response to prometryn residues was fitted with sigmoidal 3 and 4 parametric equations to the shoot biomass data as a function of the herbicide residue concentrations and was used to calculate the doses for 50% inhibition of shoot growth (ED50). In another experiment the effect of prometryn concentrations (0, 0.0033, 0.0166, 0.033, 0.066, 0.1 and 0.166 mg. kg-1soil) on soil microbial activity was determined using titration method in controlled conditions. Results and Discussion: Plant response to increasing concentration of prometryn, in general, followed a classical dose response relationship. The logistic model fitted well to the root and shoot plants response herbicide concentrations. Results showed that the shoot and root dry matter were significantly affected by increasing prometryn soil residue in all crops (plettuce>beet>barely. Based on the mechanism of action of prometryn and its best efficiency on board leaf plants control, the least biomass reduction obtained for barley is understandable. In general, this is safe to plant a susceptible species if the plant-available residue were less than the species ED10 value, and there would be a great risk for different levels of crop damage if the plant-available residue were higher than ED50 values of the species. Comparisons between species allow the safe selection of a crop that has a critical ED50 level lower than the residue level in the soil. Alternatively, planting a sensitive species could be delayed until the residue level in the soil is less than the critical level. In the Southwest areas of Iran, these crops are often sown few months after the application of a residual herbicide in the preceding crop. This large variation in plant sensitivity to prometryn residues indicates that there is potential for considerable damage to some of the rotational crops. In second experiment the results clearly indicating that in initial days of prometryn application used drastically reduced the C, N and total microbial in treated soil compared with the untreated (Control) soil. Conclusion: According to the results of this studyt the study crops are very suitable for use in bioassays for the side-effects of prometryn at low concentration rates. In this study prometryn herbicide provided symptoms of phytotoxicity to the crops, whereas seed germination of crops was not adversely affected. In the other words, this condition indicating that the application of prometryn in agricultural soil leads to decrease the total biomass of soil microorganisms at initial period. By possibly knowing the level of prometryn residual in the soil, producers could have some flexibility in crop rotations if sensitive crops such as rapeseed are to be planted following triazine herbicide use on crops

The Effect of Reduced Doses of Trifluralin on Control of ‎Common Lamsquarters (Chenopodium album L.) and Redroot ‎Pigweed (Amaranthus retroflexus L.) in Potato (Solanum ‎tuberosum L.) Fields

To evaluate the reduced concentration effect of Trifluralin (Treflan EC 33%) on common lamsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.) in potato (cv. Agria) a field experiment based on randomized complete design with three replications was carried out at the Agriculture and Natural Resources Research Station of Ardabil during 2013. Treatments were concentration of Trifluralin (0.125, 0.25, 0.5, 1, 2 and 4 Lit a.i/ha) without weed control and weeding out (as control). Sampling of weeds were performed before and after flowering of potato. Statistical analysis showed significant differences of reduced concentrations of Trifluralin on reduction of both lamsquarters and pigweed in the field. The highest reduction in percentages of weed densities, before and after flowering (91.94 and 90.34 percent, respectively) were achieved by using 4 Lit a.i/ha of Trifluralin. Application 4 Lit a.i/ha of Trifluralin at before and after flowering reduced common lamsquarters density by 87.13 and 86.04 percentages, respectively. Application 4 Lit a.i/ ha Trifluralin at befor and after flowering reduced pigweed density by more than 90 percent. Experimental results also showed that different concentrations of Trifluralin had significant effect on mean tuber weight per plant, and potato tuber yield. The highest mean weight of tuber per plant, yield per plant and potato tuber yield was obtained at 2 Lit a.i/ha Trifluralin concentration, while it was not significantly different from that of 4 Lit a.i/ ha. Generally, application of 2 and 4 Lit a.i/ha Trifluralin incereased tuber yield by 51.85 and 50.74 percents respectively

Absorption and Translocation of Dicamba in Dicamba-Tolerant Wild Tomato

Herbicide tolerance is commonly associated with reduced absorption and translocation of the herbicide; we hypothesized that the mechanism of dicamba tolerance in wild tomato (Solanum lycopersicum) accessions is due to these. The absorption and translocation of dicamba were investigated at a drift rate of 2.8 g ae ha-1, in three predetermined dicamba-tolerant wild accessions (TOM199, TOM198, and TOM300), and compared with two dicamba-susceptible (DS) commercial tomato cultivars [Money Maker (MM) and Better Boy (BB)]. Dicamba was quantified in three different parts of the tomato plant: two upper leaves, two lower leaves, and the roots, at 1, 3, and 7 days after treatment (DAT). Both MM and BB absorbed more dicamba then all the three DT accessions. The overall translocation pattern of dicamba was similar between DS cultivars and DT accessions, thus suggesting that tolerance to dicamba in wild accessions may not be associated with reduced translocation, but instead with reduced uptake of the herbicide. Additionally, reduced dicamba absorption in DT accessions may be attributed to their leaf characteristics, such as the presence of narrower leaves (3.42 leaf length/width ratio) and higher trichome density (20 no. mm-2) in DT accessions, than compared to DS cultivars (1.92 leaf length/width ratio, and 8 no. mm-2 trichome density).The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Targeted delivery of essential oils of Salvia officinalis L to AGS cancer cells using PLA-spermine-PEG-FA

The MTT test was used in this study to evaluate anticancer potential of Salvia officinalis L's essential oil on AGS cells. The results showed that the Salvia officinalis L's essential oil has high potential anticancer activity against AGS cells. To improve the solubility of the essential oil and its targeted administration to AGS cells, poly lactic acid-spermine-poly ethylene glycol-folic acid (PLA-Spermine-PEG-FA) (FPSP) was utilized. For this purpose, Salvia officinalis L's essential oil and silver nanoparticles were encapsulated into the PLA-Spermine-PEG-FA (FPSP) using the solvent diffusion technique. Then, using transmission electron microscope (TEM) and dynamic light scattering (DLS), respectively, morphology, zeta potential, as well as average particle size characteristics of the nanoparticles were evaluated. The FPSP/essential oil nanoparticles (FPSP/EO) were spherical in shape and had an average particle size of 200–300 nm. The mean particle dimensions for both PSP/silver/EO and FPSP/silver/EO nanoparticles assemblies are measured at 236.52 ± 22.64 nm and 248.95 ± 28.17 nm, respectively. The results showed that the zeta potential values for PSP/silver/EO and FPSP/silver/EO were −18.3 ± 0.7 mV and −20.6 ± 1.3 mV, respectively. The results of this test showed that FPSP/Silver/EO significantly reduced the percentage of AGS cell viability better than EO and PSP/Silver/EO. The best treatment in this experiment was FPSP/Silver/EO at a concentration of 50 μL/mL and time 72 h. The minimum value of IC50 in FPSP/Silver/EO was observed as 21.11 μL/mL in 72 h