Quinclorac controls crabgrass (Digitaria spp.) in cool- and warm-season turfgrass species. Herbicide-resistant smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] biotypes have evolved due to recurrent usage of quinclorac. Two Mississippi populations (MSU1 and MSU2) of D. ischaemum were characterized using standard greenhouse dose–response screens to assess their resistance relative to known susceptible populations. Subsequent investigations explored mechanisms of resistance, including examining cyanide accumulation, glutathione S-transferase (GST) activity, and the potential involvement of cytochrome P450s in MSU1, MSU2, and a susceptible (SMT2). Resistant populations MSU1 and MSU2 required 80 and 5 times more quinclorac, respectively, to reach 50% biomass reduction than susceptible populations. The SMT2 biotype accumulated three times more cyanide than the resistant MSU1 and MSU2 populations. GST activity was elevated in resistant MSU1 and MSU2 populations. Furthermore, quinclorac concentrations in treated resistant populations were elevated when plants were pretreated with the P450 inhibitor malathion. These findings suggest a non–target site based mechanism of resistance involving the accumulation of cyanide. This may provide a scientific basis for understanding the occurrence of quinclorac-resistant D. ischaemum, although further research is needed to investigate potential target-site mechanisms of resistance.

Palmer amaranth (Amaranthus palmeri S. Watson), a dioecious summer annual species, is one of the most troublesome weeds in U.S. cropping systems. The evolution of resistance to protoporphyrinogen oxidase inhibitors in A. palmeri biotypes is a major cause of concern to soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) growers in the midsouthern United States. The objective of this study was to confirm and characterize the non–target site mechanism in a fomesafen-resistant accession from Randolph County, AR (RCA). A dose–response assay was conducted to assess the level of fomesafen resistance, and based on the GR50 values, the RCA accession was 18-fold more resistant to fomesafen than a susceptible (S) biotype. A TaqMan allelic discrimination assay and sequencing of the target-site genes PPX2 and PPX1 revealed no known or novel target-site mutations. An SYBR Green assay indicated no difference in PPX2 gene expression between the RCA and S biotypes. To test whether fomesafen resistance is metabolic in nature, the RCA and the S biotypes were treated with different cytochrome P450 (amitrole, piperonyl butoxide [PBO], malathion) and glutathione S-transferase (GST) (4-chloro-7-nitrobenzofurazan [NBD-Cl]) inhibitors, either alone or in combination with fomesafen. Malathion followed by (fb) fomesafen in RCA showed the greatest reduction in survival (67%) and biomass (86%) compared with fomesafen alone (45% and 66%, respectively) at 2 wk after treatment. Interestingly, NBD-Cl fb fomesafen also resulted in low survival (35%) compared with the fomesafen-only treatment (55%). Applications of malathion or NBD-Cl preceding fomesafen treatment resulted in reversal of fomesafen resistance, indicating the existence of cytochrome P450– and GST-based non–target site mechanisms in the RCA accession. This study confirms the first case of non–target site resistance to fomesafen in A. palmeri.

Herbicide resistance is the heritable ability of a weed biotype or population to survive a herbicide application that would effectively kill a susceptible population of the weed. In the U.K. the most widespread and financially important herbicide-resistant weed is blackgrass. Investigations to elucidate the molecular mechanisms conferring herbicide resistance to blackgrass populations have been ongoing for two decades. Although the identification of target site–resistant populations has proved to be relatively straightforward (using, for example, target site assays in vitro), the study and understanding of resistance mechanisms involved in enhanced metabolism has proven to be more problematic. Research has focused on the cytochrome P450 monooxygenase and glutathione S-transferase (GST) enzyme families, both of which have been shown to be important in herbicide metabolism in many weed and crop species. GST activity and abundance are greater in a selection of herbicide-resistant blackgrass biotypes, and herbicide treatment of field populations of blackgrass results in the survival of the proportion of population possessing the greatest GST activity and abundance. In addition, GST activity in the field increases between winter and spring, and this coincides with reduced efficacy of important blackgrass herbicides. GST activities within field populations of blackgrass are highly varied, and this plasticity is discussed in relation to the development of resistant populations in field situations. This article describes research results in blackgrass and compares them with GST studies in other weed species as well as with other mechanisms for enhanced metabolism-based resistance.

Luffa cylindrica (L.) M. Roem. is an underutilized vegetable and a potential biodiesel crop for future. Its fruits are edible and used as vegetable. To aid in the selection of lines for breeding, genetic variation and structure of ten populations of L. cylindrica were determined with three morphological characters and 23 sequence-related amplified polymorphism (SRAP) markers. All the three morphological characters were found diverse among 45 accessions. The SRAP primers produced a total of 177 bands, out of which 129 were polymorphic. Informative markers assessed by different measures (polymorphism information content = 0.18, marker index = 1.26, resolving power = 2.87) will direct the selection of primers for cultivar identification in L. cylindrica. Low level of genetic differentiation among populations and higher level within populations (Gst= 0.4073, Nm= 0.7277, He= 0.124, I= 0.20) was detected that might be due to cross-pollinated nature of L. cylindrica. The clustering pattern obtained through dendrogram and principal coordinate analysis was loosely concordant with the geographical distribution. The Bayesian structure analysis indicated an admixture type of population distribution. The results designate that SRAP and morphological markers are informative for characterization of L. cylindrica and identification of distinctive cultivars.

The gilthead seabream is the most important Mediterranean aquacultured fish species. The main objective of this study was to investigate whether copper sulphate bath treatments used routinely in aquaculture have effects on important physiological functions of early life stages of the gilthead seabream (Sparus aurata). Fingerlings (80–90 days, 0.27 ± 0.06 g) were exposed to copper sulphate baths at 0, 0.25, 0.5 and 1.5 mg L−1 during 24 h. Effects on the central nervous function were evaluated analysing brain acetylcholinesterase activity (AChE). Oxidative stress was assessed by the quantification of lipid peroxidation (LP). Heat shock proteins (HSP70) were used as a general response to chemical stress, RNA/DNA ratio as an indicator of growth, and effects on detoxification function were estimated using glutathione–S-transferases activity (GST). Exposure of S. aurata fingerlings to copper sulphate induced increased lipid peroxidation. In contrast, there were no significant changes in AChE activity, HSP70 levels, RNA/DNA ratio or GST activity. Particularly, the absence of response in GST activity points towards a limited extent of the putative damage caused by the treatments at the highest doses (evidenced through the levels of peroxidation), since this enzyme is directly implicated in detoxification processes involving redox cyclic products. The results suggest that copper sulphate baths at the conditions tested are safe treatments for S. aurata fingerlings.