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Papers by Eshagh Keshtkar
Iranian Journal of Field Crop Science, 2010
Review of Scientific Instruments, 1987
... of Form-var foils. The work at Argonne was supported by the US Department of Energy, Office o... more ... of Form-var foils. The work at Argonne was supported by the US Department of Energy, Office of Basic Energy Sciences, un-der Contract W-31-109-ENG-38. *> Present address: Technion, Haifa, Israel 32000. 'DS Gemmell, Chem. Rev. 80, 301 (1980). 2E. P. Kanter, in ...
Journal of Plant Protection Research, Dec 1, 2021
Crop Protection, 2020
Abstract Increasing the diversity in the sites of action of herbicides is an important method for... more Abstract Increasing the diversity in the sites of action of herbicides is an important method for delaying and preventing herbicide resistance in weed populations. Benzoylprop-ethyl, a lipid biosynthesis inhibitor, is used to increase the diversity of herbicide sites of action and control ACCase- and ALS-resistant Avena sterilis subsp. ludoviciana (Durieu.) Gillet & Magne) populations in Iran. Drought stress, especially in arid and semiarid areas, affects weed physiology and performance of herbicides. Accordingly, a series of dose-response assays was conducted to evaluate the efficacy of benzoylprop-ethyl under drought- (60% Field Capacity) and non-drought-stress (90% Field Capacity) conditions on A. sterilis subsp. ludoviciana. Also, some biochemical and physiological traits of A. sterilis subsp. ludoviciana including leaf chlorophyll content, leaf greenness index, photosynthesis rate and stomatal conductance were investigated under the drought and non-drought regimes. The efficacy of benzoylprop-ethyl decreased significantly under drought condition. The effective dose reducing dry weight by 90% in relation to the untreated control (i.e., ED90) for the drought-stressed plants was significantly (P
The experiment was conducted under a controlled environment to study the effects of different tem... more The experiment was conducted under a controlled environment to study the effects of different temperature regimes (15/10°C, 20/15°C, and 25/20°C day/night) and sowing depths (0, 2, 4, and 6 cm) on the seedling emergence and early growth (height gain) of wheat (cv. Marvdasht) and wild barley (Hordeum spontaneum).The cumulative emergence and plant height gain over time were modeled with the use of a logistic function. For a particular temperature regime, the maximum percentage emergence (Emax) of wheat was higher than that of wild barley across all sowing depths. The maximum and minimum Emax values for both species occurred at 20/15°C and 25/20°C, respectively.The time taken to reach 50% of the Emax (i.e. E50) increased with the sowing depth in both species under all temperature regimes. The E50 of wild barley was greater than that of wheat for all temperature regimes, with maximum differences observed at 20/15°C. The greatest maximum plant height (Hmax) was observed at the surface pl...
The spread of weed resistance to herbicides is expanding in Iran; therefore, monitoring of resist... more The spread of weed resistance to herbicides is expanding in Iran; therefore, monitoring of resistance to the most commonly used herbicides and evaluation of cross-resistance to the herbicides were carried out on 38 canarygrass accessions collected from wheat fields in five provinces (Golestan, Fars, Khuzestan, Ardabil and Tehran provinces) of Iran. The whole plant screening test was conducted with four replications in the greenhouse of Iranian Research Institute of Plant Protection in 2019. Plants at the two- to -three leaves stage were exposed to the recommended field dose of herbicides. Four weeks after spraying, the percentage of fresh and dry weights and plants survival were measured. Of the 38 accessions, 13 (34%), eight (21%), two (5%) and one (about 2.5%) accessions were classified to being high resistant and suspected resistant to mesosulfuron+iodosulfuron+mefenpyr-diethyl (Atlantis), clodinafop-propargyl (Topik), pinoxaden (Axial), and mesosulfuron+iodosulfuron+difloficane+...
Seed Science Research
Germination experiments are becoming increasingly complex and they are now routinely involving se... more Germination experiments are becoming increasingly complex and they are now routinely involving several experimental factors. Recently, a two-step approach utilizing meta-analysis methodology has been proposed for the estimation of hierarchical models suitable for describing data from such complex experiments. Step 1 involves fitting models to data from each sub-experiment, whereas Step 2 involves combination estimates from all model fits obtained in Step 1. However, one shortcoming of this approach was that visualization of resulting fitted germination curves was difficult. Here, we describe in detail an improved two-step analysis that allows visualization of cumulated data together with fitted curves and confidence bands. Also, we demonstrate in detail, through two examples, how to carry out the statistical analysis in practice.
Weed Science
Quantifying the level of eco-physiological, biochemical, and agronomical fitness of herbicide-res... more Quantifying the level of eco-physiological, biochemical, and agronomical fitness of herbicide-resistant (R) and -susceptible (S) weeds is useful for understanding the evolutionary development of herbicide resistance, but also for implementing herbicide-resistance management strategies. Although germination is a key fitness component in the life cycle of weeds, germinability of S and R weeds has rarely been evaluated under stressful conditions. Germinability traits of S and non-target-site resistant sub-populations of blackgrass (Alopecurus myosuroides Huds.) sharing closely related genetic background were tested under salinity, drought stress, and accelerated seed aging (i.e., exposed to 100% relative humidity at 45 ºC from 0 to 134 hours) conditions. In addition, the activity of three antioxidant enzymes and protein concentration of accelerated aged seeds of the sub-populations were studied. There were no differences in maximum seed germination (G max ) and time to 50% germination ...
Weed Science
In recent years, herbicide resistance has attracted much attention as an increasingly urgent prob... more In recent years, herbicide resistance has attracted much attention as an increasingly urgent problem worldwide. Unfortunately, most of that effort was focused on confirmation of resistance and characterization of the mechanisms of resistance. For management purposes, knowledge about biology and ecology of the resistant weed phenotypes is critical. This includes fitness of the resistant biotypes compared with the corresponding wild biotypes. Accordingly, fitness has been the subject of many studies; however, lack of consensus on the concept of fitness resulted in poor experimental designs and misinterpretation of the ensuing data. In recent years, methodological protocols for conducting proper fitness studies have been proposed; however, we think these methods should be reconsidered from a herbicide-resistance management viewpoint. In addition, a discussion of the inherent challenges associated with fitness cost studies is pertinent. We believe that the methodological requirements fo...
Seed Science Research
In recent years germination experiments have become more and more complex. Typically, they are re... more In recent years germination experiments have become more and more complex. Typically, they are replicated in time as independent runs and at each time point they involve hierarchical, often factorial experimental designs, which are now commonly analysed by means of linear mixed models. However, in order to characterize germination in response to time elapsed, specific event-time models are needed and mixed model extensions of these models are not readily available, neither in theory nor in practice. As a practical workaround we propose a two-step approach that combines and weighs together results from event-time models fitted separately to data from each germination test by means of meta-analytic random effects models. We show that this approach provides a more appropriate appreciation of the sources of variation in hierarchically structured germination experiments as both between- and within-experiment variation may be recovered from the data.
Weed Science
Seedling emergence traits of susceptible (S) and resistant (R) blackgrass subpopulations isolated... more Seedling emergence traits of susceptible (S) and resistant (R) blackgrass subpopulations isolated from a single non–target-site resistant (NTSR) population were studied in controlled conditions. The seedling emergence of the R subpopulation was lower and slower than that of the S subpopulation, especially at low temperature and deep burial. The burial depth inhibiting final emergence by 50% for the R subpopulation was significantly lower than that of the S subpopulation at low temperature. The present study revealed that under suboptimal conditions the NTSR loci conferring herbicide resistance were correlated with a fitness cost in relation to seedling emergence traits. The results suggest that deep soil cultivation and delayed sowing of autumn-sown crops can hamper germination of the R more than of the S subpopulation and thus potentially reduce the prevalence of the R subpopulation in the blackgrass population.
Iranian Journal of Field Crop Science, 2010
Review of Scientific Instruments, 1987
... of Form-var foils. The work at Argonne was supported by the US Department of Energy, Office o... more ... of Form-var foils. The work at Argonne was supported by the US Department of Energy, Office of Basic Energy Sciences, un-der Contract W-31-109-ENG-38. *> Present address: Technion, Haifa, Israel 32000. 'DS Gemmell, Chem. Rev. 80, 301 (1980). 2E. P. Kanter, in ...
Journal of Plant Protection Research, Dec 1, 2021
Crop Protection, 2020
Abstract Increasing the diversity in the sites of action of herbicides is an important method for... more Abstract Increasing the diversity in the sites of action of herbicides is an important method for delaying and preventing herbicide resistance in weed populations. Benzoylprop-ethyl, a lipid biosynthesis inhibitor, is used to increase the diversity of herbicide sites of action and control ACCase- and ALS-resistant Avena sterilis subsp. ludoviciana (Durieu.) Gillet & Magne) populations in Iran. Drought stress, especially in arid and semiarid areas, affects weed physiology and performance of herbicides. Accordingly, a series of dose-response assays was conducted to evaluate the efficacy of benzoylprop-ethyl under drought- (60% Field Capacity) and non-drought-stress (90% Field Capacity) conditions on A. sterilis subsp. ludoviciana. Also, some biochemical and physiological traits of A. sterilis subsp. ludoviciana including leaf chlorophyll content, leaf greenness index, photosynthesis rate and stomatal conductance were investigated under the drought and non-drought regimes. The efficacy of benzoylprop-ethyl decreased significantly under drought condition. The effective dose reducing dry weight by 90% in relation to the untreated control (i.e., ED90) for the drought-stressed plants was significantly (P
The experiment was conducted under a controlled environment to study the effects of different tem... more The experiment was conducted under a controlled environment to study the effects of different temperature regimes (15/10°C, 20/15°C, and 25/20°C day/night) and sowing depths (0, 2, 4, and 6 cm) on the seedling emergence and early growth (height gain) of wheat (cv. Marvdasht) and wild barley (Hordeum spontaneum).The cumulative emergence and plant height gain over time were modeled with the use of a logistic function. For a particular temperature regime, the maximum percentage emergence (Emax) of wheat was higher than that of wild barley across all sowing depths. The maximum and minimum Emax values for both species occurred at 20/15°C and 25/20°C, respectively.The time taken to reach 50% of the Emax (i.e. E50) increased with the sowing depth in both species under all temperature regimes. The E50 of wild barley was greater than that of wheat for all temperature regimes, with maximum differences observed at 20/15°C. The greatest maximum plant height (Hmax) was observed at the surface pl...
The spread of weed resistance to herbicides is expanding in Iran; therefore, monitoring of resist... more The spread of weed resistance to herbicides is expanding in Iran; therefore, monitoring of resistance to the most commonly used herbicides and evaluation of cross-resistance to the herbicides were carried out on 38 canarygrass accessions collected from wheat fields in five provinces (Golestan, Fars, Khuzestan, Ardabil and Tehran provinces) of Iran. The whole plant screening test was conducted with four replications in the greenhouse of Iranian Research Institute of Plant Protection in 2019. Plants at the two- to -three leaves stage were exposed to the recommended field dose of herbicides. Four weeks after spraying, the percentage of fresh and dry weights and plants survival were measured. Of the 38 accessions, 13 (34%), eight (21%), two (5%) and one (about 2.5%) accessions were classified to being high resistant and suspected resistant to mesosulfuron+iodosulfuron+mefenpyr-diethyl (Atlantis), clodinafop-propargyl (Topik), pinoxaden (Axial), and mesosulfuron+iodosulfuron+difloficane+...
Seed Science Research
Germination experiments are becoming increasingly complex and they are now routinely involving se... more Germination experiments are becoming increasingly complex and they are now routinely involving several experimental factors. Recently, a two-step approach utilizing meta-analysis methodology has been proposed for the estimation of hierarchical models suitable for describing data from such complex experiments. Step 1 involves fitting models to data from each sub-experiment, whereas Step 2 involves combination estimates from all model fits obtained in Step 1. However, one shortcoming of this approach was that visualization of resulting fitted germination curves was difficult. Here, we describe in detail an improved two-step analysis that allows visualization of cumulated data together with fitted curves and confidence bands. Also, we demonstrate in detail, through two examples, how to carry out the statistical analysis in practice.
Weed Science
Quantifying the level of eco-physiological, biochemical, and agronomical fitness of herbicide-res... more Quantifying the level of eco-physiological, biochemical, and agronomical fitness of herbicide-resistant (R) and -susceptible (S) weeds is useful for understanding the evolutionary development of herbicide resistance, but also for implementing herbicide-resistance management strategies. Although germination is a key fitness component in the life cycle of weeds, germinability of S and R weeds has rarely been evaluated under stressful conditions. Germinability traits of S and non-target-site resistant sub-populations of blackgrass (Alopecurus myosuroides Huds.) sharing closely related genetic background were tested under salinity, drought stress, and accelerated seed aging (i.e., exposed to 100% relative humidity at 45 ºC from 0 to 134 hours) conditions. In addition, the activity of three antioxidant enzymes and protein concentration of accelerated aged seeds of the sub-populations were studied. There were no differences in maximum seed germination (G max ) and time to 50% germination ...
Weed Science
In recent years, herbicide resistance has attracted much attention as an increasingly urgent prob... more In recent years, herbicide resistance has attracted much attention as an increasingly urgent problem worldwide. Unfortunately, most of that effort was focused on confirmation of resistance and characterization of the mechanisms of resistance. For management purposes, knowledge about biology and ecology of the resistant weed phenotypes is critical. This includes fitness of the resistant biotypes compared with the corresponding wild biotypes. Accordingly, fitness has been the subject of many studies; however, lack of consensus on the concept of fitness resulted in poor experimental designs and misinterpretation of the ensuing data. In recent years, methodological protocols for conducting proper fitness studies have been proposed; however, we think these methods should be reconsidered from a herbicide-resistance management viewpoint. In addition, a discussion of the inherent challenges associated with fitness cost studies is pertinent. We believe that the methodological requirements fo...
Seed Science Research
In recent years germination experiments have become more and more complex. Typically, they are re... more In recent years germination experiments have become more and more complex. Typically, they are replicated in time as independent runs and at each time point they involve hierarchical, often factorial experimental designs, which are now commonly analysed by means of linear mixed models. However, in order to characterize germination in response to time elapsed, specific event-time models are needed and mixed model extensions of these models are not readily available, neither in theory nor in practice. As a practical workaround we propose a two-step approach that combines and weighs together results from event-time models fitted separately to data from each germination test by means of meta-analytic random effects models. We show that this approach provides a more appropriate appreciation of the sources of variation in hierarchically structured germination experiments as both between- and within-experiment variation may be recovered from the data.
Weed Science
Seedling emergence traits of susceptible (S) and resistant (R) blackgrass subpopulations isolated... more Seedling emergence traits of susceptible (S) and resistant (R) blackgrass subpopulations isolated from a single non–target-site resistant (NTSR) population were studied in controlled conditions. The seedling emergence of the R subpopulation was lower and slower than that of the S subpopulation, especially at low temperature and deep burial. The burial depth inhibiting final emergence by 50% for the R subpopulation was significantly lower than that of the S subpopulation at low temperature. The present study revealed that under suboptimal conditions the NTSR loci conferring herbicide resistance were correlated with a fitness cost in relation to seedling emergence traits. The results suggest that deep soil cultivation and delayed sowing of autumn-sown crops can hamper germination of the R more than of the S subpopulation and thus potentially reduce the prevalence of the R subpopulation in the blackgrass population.