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The level of resistance and patterns of cross-resistance to clodinafop, sethoxydim, and pinoxaden were examined in 12 putative resistant and one susceptible populations of winter wild oat (Avena ludoviciana) collected from Fars Province, in the southwest of Iran. The responses of biomass and length of coleoptiles to the increasing dosages of the three herbicides were determined in both whole-plant and seed bioassays. In the whole-plant bioassay, all 12 putative resistant populations were found to be resistant to clodinafop with resistance ratios (R/S) ranging from 1.76 to >47.04. Most clodinafop-resistant populations exhibited low levels of cross-resistance to sethoxydim. Three highly sethoxydim-resistant populations, F2, S2, and ES4, were slightly resistant to clodinafop. Six populations (M1, M2, F2, S2, S4, and ES4) showed high cross-resistance to pinoxaden with R/S values as large as 10.73 to 40.29. A highly clodinafop-resistant population, M2, was more sensitive to pinoxaden than the susceptible population. The results of the seed bioassay resembled those obtained from the whole-plant experiment suggesting seed bioassay as an inexpensive, rapid method for screening-resistant genotypes.

The development of herbicide-resistant weed species is a threat to the agricultural industry in Iran and the world. The first step in managing this issue is the identification of herbicideresistant populations. In this study, 124 and 45 grass weed accessions, including winter wild oat, annual ryegrass, and littleseed canarygrass, were collected from wheat and canola fields, respectively, in different provinces of Iran. The accessions were screened using commonly used herbicides at the three- to four-leaf stage. The weed accessions collected from wheat fields were exposed to the recommended field dose of clodinafop-propargyl, pinoxaden, mesosulfuron-methyl+iodosulfuron-methyl-Na, and mesosulfuron-methyl+iodosulfuronmethyl- Na+diflufenican. Similarly, the canola grass weeds were treated with haloxyfop-Rmethyl, sethoxydim, cycloxydim, and clethodim. The experiment was carried out based on a completely randomized design with four replications under controlled greenhouse conditions. Four weeks after spraying, the fresh weight of the populations was measured. The results showed that 52, 9, 19, and 17% of grass weeds in wheat fields were resistant to clodinafop-propargyl, pinoxaden, mesosulfuron-methyl+iodosulfuron-methyl-Na, and mesosulfuron-methyl+iodosulfuron-methyl-Na+diflufenican, respectively. Morover, 47, 47, and 22% of the canola grass weeds showed resistance to haloxyfop-R-methyl, sethoxydim, and clethodim, respectively; while they were susceptible to cycloxydim. Cross-resistance to selective herbicides in canola was observed in 36% of the tested grass weed species. Additionally, multiple resistance to both ACCase and ALS inhibitors in wheat fields was identified in 13% of winter wild oat and 82% of annual ryegrass populations, respectively. It is recommended to avoid the use of herbicides with the same mechanism of action for controlling grass weeds in areas where the wheat and canola rotation system is prevalent. [ABSTRACT FROM AUTHOR]

Introduction Chlorophyll fluorescence induction is a rapid and noninvasive technique for measuring photosynthetic electron transport in plants. Recognition of fluorescence curves such as Kautsky curves is a useful tool for quantifying herbicide effects. In general, since one of the goals of measuring chlorophyll fluorescence is the early detection of the effects of herbicide before its apparent effects on weed. PSII inhibiting herbicides resistance results from a mutation in the chloroplast genome, reducing the rate of electron transport between QA and QB in PS II. Materials and Methods The seeds pre-germinated in Petri dishes at 28±2 °C in 16/8 hr (light/dark) photoperiod for 72 hr. The pre-germinated seeds were sown in pots (with 10 cm diameter) containing loam: sand 2:1 mixture (v/v). Pots were transferred to a greenhouse and grown at 30 °C and 20 °C day and night temperatures, respectively, with artificial light to provide a 16-h photoperiod. Pots were irrigated regularly to avoid any moisture stress. Ten days after planting (DAP), they were thinned to two seedlings per pot. Twenty days after weed emergence, seedlings of the pots were subjected to the post emergence application of ametryn. Different ranges of ametryn rates were used for the resistant (0, 10, 30, 100, 300, 1000, 3000, 10000 and 30000 g ai ha-1 and susceptible (0, 1, 10, 30, 100, 300, 1000 g ai ha-1) populations because of the difference in dose-response among populations. Nonionic surfactant 0.25% (v/v) was applied with the herbicide at the time of spraying. The sprayer was calibrated to deliver 220 L ha-1 at pressure of 2 atm. The aboveground biomass was harvested 28 days after treatment (DAT) and weighed. In order to analyze the data and draw the shapes, Gompertz function and SigmaPlot11 and R soft wares were used. PEA Plus software, also, was used to output the chlorophyll fluorescence data recorded during the experiment. Results and Discussion The results showed that Fvj was more sensitivity to the application of ametryn in the tested populations. So that four hours after the application of ametryn, Fvj, in some populations, especially susceptible population (24.47 g ai ha-1), decreased significantly. Regarding ED50 values based on fresh weight of populations, the highest amount of ED50 belonged to R4 (10289 g ai ha-1), R1 (6844.6 g ai ha-1), R3 (4770 g ai ha-1) and R2 (3041.0 g ai ha-1), respectively. Estimated ED50 values for Fvj susceptible and resistant populations were, in some cases, far lower than estimated ED50 values for fresh weight of populations at 28 days after treatment with herbicides. In general, the linear relationship between the above parameter and the fresh weight of the populations indicates a strong correlation between these parameters. There were differences among the resistant and susceptible populations in the application of herbicide in terms of the slope of the curve of fvj. So that the curve slope in R1 and R2 biotypes was faster than other populations. In susceptible population response, more correlation was observed between the above parameters. The purpose of this parameter was to show that chlorophyll fluorescence parameters, such as fresh weight assay or weed dry weight, can predict the effect of herbicides. Thus, the researchers are able to evaluate the herbicide's impact on the plants by spending less time and cost. Conclusion Since the main effect of photosystem II inhibiting herbicides is in the J stage (Fvj). Therefore, it is possible to use the Fvj parameter, which most likely shows the changes in electron transfer in the electron transfer chain in photosystem II. The most resistant populations (R1 and R4) based on the measurement of fresh weight, in the analysis based on the Fvj parameter, like other resistant populations, showed the significant difference with the susceptible population. Also, the sensitivity of the susceptible population response to herbicide application based on the Fvj parameter was much higher than that of fresh weight. So that it enables the researcher to quickly distinguish among the susceptible and resistant populations to the mentioned herbicides. [ABSTRACT FROM AUTHOR]

Weeds are one of the most important limiting factors in the production of chickpea (Cicer arietinum) in Iran, especially in autumn sown chickpea. Weed density and biomass in autumn chickpea are seven and two and a half times higher than the spring chickpea, respectively. The weed damage to chickpea in Tabriz, Kermanshah and West Azerbaijan was estimated at 48.3, 57 and 36%, respectively. Sixty-four weed species were identified in chickpea fields. Convolvulus arvensis L. and Galium tricornutum Dandy have the highest presence in chickpea fields. Pyridate and linuron are the only herbicides registered for use in chickpea fields in Iran. However, research results show that fomesafen and isoxaflutole are the most appropriate herbicides for chickpea fields. Oxyfluorfen, imazethapyr, metribuzin, trifluralin, simazine, terbutryn and pendimethalin are the major herbicides studied in weed control research. The combination of herbicides and mechanical control is one of the effective methods to reduce weeds. Hand weeding and cultivation between rows are the most effective mechanical methods of weed control. High nitrogen enhances weed dry weight. Safflower and barley residues reduce weed populations and biomass. Barley-chickpea and wheat-chickpea intercropping systems increase chickpea yield together with proper weed control. In future research, more attention should be paid to surfactants to reduce the use of herbicides, rotation crops and integrated weed management in chickpea. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to control field dodder (Cuscuta campestris Y.) in sugar beet, experiments were done in greenhouse and field of Sugar Beet Research Institute, Karaj, Iran. In greenhouse test, the impact of direct seed sowing, transplanting of seedlings at two and eight-leaf stages (factor A) and dodder seed sowing with no distance and at 7 cm distance from the host (factor B) on control of the weed was studied in a factorial experiment based on completely randomized design with three replications. In the field test, the effects of direct seed sowing and transplanting of sugar beet seedlings (factor A) and application of four post-emergence herbicides (factor B) on control of the weed were evaluated in a factorial experiment based on randomized complete block design with four replications. In the greenhouse experiment, percentage of infection was decreased by increasing the distance between the parasite and the host. In the field experiment, the degree of host infection by dodder was recorded before and after application of the herbicides. Fresh and dry weight of dodder and root yield of sugar beet was measured. The method of cultivation was significantly effective on the ability to deploy of dodder on the host so that in direct sowing of sugar beet seed, the ability of dodder to colonize the host was found to be 3.5 times higher than that of transplanting method. Root yield was significantly influenced by the sowing method and showed 2.5 times increase in transplanting method. The biomass of the parasite established on the host demonstrated 7.5 times decrease compared to the direct seed sowing method. [ABSTRACT FROM AUTHOR]