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Background/Objectives: Johnsongrass (Sorghum halepense) is an erect tetraploid, perennial, C4 grass weed species categorized among the world's most noxious weeds due to its high competitive ability against crops and the increased number of field-evolved herbicide-resistant populations. The aim of the present study was to assess the growth rate and performance of resistant (R) johnsongrass genotypes hosting Trp574Leu target-site cross-resistance at ALS gene, inhibiting various herbicides, compared to susceptible (S) conspecific weeds, in the absence and presence of corn or sunflower antagonism. Methods: The aboveground biomass, tiller, and rhizome production ability of one S and one R johnsongrass population with a Trp574-Leu substitution conferring cross-resistance to ALS-inhibiting herbicides were compared under non-competitive conditions. Furthermore, the competitive ability of these two johnsongrass populations against corn or sunflower was determined in a target-neighborhood design. Results: The S and R johnsongrass populations displayed similar growth rates concerning aboveground biomass and tiller number, whereas the R population displayed a slightly greater growth rate for rhizome production compared to the S population. Both populations grown with corn produced more aboveground biomass than the ones grown with sunflowers. The aboveground biomass of corn was reduced to a greater extent than sunflower by the presence of both johnsongrass populations, while both crops were affected more by the S than by the R population. Conclusions: Although the inheritance and the genetic background of plant materls were not addressed, the findings of this study indicate clearly that the growth rate and competitive ability of the ALS-resistant johnsongrass population are not associated with the resistance mechanism involved. [ABSTRACT FROM AUTHOR]

Block Kriging (a spatial interpolation method) and log10 transformation were compared for their effectiveness in reducing relative variance (coefficient of variance: CV) and estimate mean values in all harvested maize plants grown in three randomly taken field plots and for harvested plants after removing the "edge or margin" ones. The results showed that log10 transformation reduced CVs of all harvested original fresh weight (FW) plant data in the three plots from 35.6–41.6% (original data) to 6.0–7.5%, while the respective CVs due to Block Kriging were reduced to 14.5–19.9%. The back-log10-transformed means of all harvested FW plant data were reduced by 6.8–9.4%, while the respective reduction for plants excluding the margin ones was 1.3–8.3%. The Block Kriging means for all harvested FW plant data were reduced only by 0.3–0.4%, while the respective means of the harvested plants excluding margin ones were increased by 0.4–4.3%. These findings strongly suggest that Block Kriging should be preferred over the log10 transformation method (used so far by agroscientists) as it managed to effectively reduce variability in crop data and estimate missing values that provide more precise and reliable estimates of corn yield for farmers. [ABSTRACT FROM AUTHOR]

Three perennial ryegrass (Lolium perenne) populations (R1, R2, and R3) with suspected resistance (R) to acetolactate synthase (ALS) or acetyl-CoA carboxylase (ACCase) herbicides were collected from wheat (Triticum aestivum) fields in northwestern Greece to study the underlying mechanisms of resistance and their impact on growth rate and competitive ability against wheat. Preemergence and postemergence plant dose–response assays showed that the R1 population was cross-resistant to the ALS inhibitors chlorsulfuron, mesosulfuron + iodosulfuron, and pyroxsulam, but susceptible (S) to imazamox. However, all populations were susceptible to the ACCase inhibitors clodinafop-propargyl, clethodim, diclofop-methyl, and pinoxaden. The analysis of the ALS gene sequence revealed a substitution of Pro197 by His or Leu in the ALS enzyme in L. perenne, which is reported for the first time in this weed and indicates a potential mechanism of target site-mediated resistance. The R1 population grown in the absence or presence of wheat competition displayed similar aboveground biomass and tiller number trends, and therefore similar estimated growth rates. In addition, the aboveground biomass of wheat was similarly reduced by both the R1 and S populations, supporting the evidence of their similar competitive ability against wheat. In general, these findings indicate that there is no clear evidence for the fitness advantage of R1 over the S population. [ABSTRACT FROM AUTHOR]

Whole-plant response experiments in pots and field experiments over two years were conducted to study the resistance levels and chemical control options of sterile oat (Avena sterilis L.) in typical wheat production areas of northern Greece. Data revealed high levels of resistance to the ACCase-inhibiting herbicides clodinafop-propargyl and fenoxaprop-p-ethyl in all sterile oat populations, noticeable levels of resistance of some populations to tralkoxydim and pinoxaden, and high susceptibility of four out of the five populations to the prepackage mixture [mesosulfuron + iodosulfuron]. The addition of chlorpyrifos did not improve the efficacy of all herbicides against the resistant populations, implying target-site resistance in the populations tested rather than resistance due to P450-mediated enhanced herbicide metabolism. These results indicated that all populations were at least four times more resistant to clodinafop-propargyl, fenoxaprop-p-ethyl and diclofop-methyl than the susceptible populations, but noticeable levels of resistance of some sterile oat populations to tralkoxydim, pinoxaden and the prepackage mixture [mesosulfuron + iodosulfuron] were also recorded. However, viable options for chemical control of this weed still exist. [ABSTRACT FROM AUTHOR]

Plant responses to glyphosate applied at different doses were examined for one glyphosate resistant (R) and one glyphosate susceptible (S) population of Conyza albida and C. bonarienis. Growth rates and development stages of five R C. albida and three R C. bonarienis populations were also compared with those of their respective S counterparts to investigate the possible impact of the glyphosate resistance trait on their fitness. The GR50 values for C. albida R (3.94-5.22 kg a.i. · ha-1) and S (0.24-0.31 kg a.i. · ha-1) populations were higher than those of C. bonariensis R (0.60-1.51 kg a.i. · ha-1) and S (0.10-0.13 kg a.i. · ha-1). The growth rate (slope b) of one R C. albida population was lower than the respective S and other R populations, while growth rates of most R and S C. bonariensis populations were similar. Some R populations showed inconsistent differences in some development stages when compared to those of the S ones, which cannot be attributed to the glyphosate resistance trait. [ABSTRACT FROM AUTHOR]

BACKGROUND Studies were carried out to elucidate the mechanism of resistance to ALS-inhibiting herbicides in 29 Echinochloa accessions from water-seeded rice fields of northern Greece and to discriminate the Echinochloa species. RESULTS Two E. oryzicola accessions were found to be cross-resistant to penoxsulam, bispyribac-sodium, imazamox, foramsulfuron, nicosulfuron and rimsulfuron, whereas all accessions were susceptible (S) to profoxydim. Sequencing of the ALS gene revealed that resistant (R) accessions had a Trp574Leu mutation, which was also confirmed by TspRI endonuclease digestion. Use of cpDNA sequence comparison analysis of Echinochloa species discriminated successfully E. crus-galli and E. oryzicola accessions. CONCLUSION This is the first report of Echinochloa oryzicola cross-resistance to ALS-inhibiting herbicides as a result of Trp574Leu mutation. The cpDNA sequence comparison analysis is a reliable tool for discrimination of conventionally classified E. crus-galli and E. oryzicola accessions. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]