Herbicide resistance is increasing in incidence among weed populations and poses a threat to food security. In Sunflower County, MS, a population of junglerice was identified with resistance to four herbicides, fenoxaprop-P-ethyl, imazamox, quinclorac, and propanil, each representing a different mechanism of action. The target site of fenoxaprop-P-ethyl, acetyl coenzyme A carboxylase (ACCase), was investigated. The ACCase contained none of the known resistance-conferring point mutations and an enzyme assay revealed no difference in response to increasing levels of fenoxaprop-P-ethyl between the resistant biotype and a sensitive biotype, indicating that the ACCase enzyme in the resistant biotype was sensitive to the herbicide. Whole-plant dose response assays in the presence and absence of cytochrome P450 and glutathione-S-transferase (GST) inhibitors did not increase efficacy of fenoxaprop-P-ethyl in the resistant biotype. However, when malathion, a cytochrome P450 inhibitor, was applied with imazamox or quinclorac, a reduction in resistance was observed in the resistant biotype, suggesting that a cytochrome P450 was important to the resistance mechanism for these two herbicides. RNA was isolated from the resistant and sensitive biotypes before and one hour after imazamox treatment for RNA-seq analysis. The reads from all samples were pooled to assemble the first E. colona leaf transcriptome. Differential gene expression analysis comparing untreated and treated samples for both biotypes revealed that several stress response genes were upregulated following herbicide exposure. A time course examining six of these genes showed that expression peaked between 4 and 12 hours and then dropped to untreated levels by 48 hours. Comparison of untreated resistant and sensitive plants revealed that a kinase and GST were significantly upregulated in the resistant biotype and an F-box protein was significantly downregulated. SNP analysis of cytochrome P450 sequences identified several nonsynonymous point mutations of interest including two transcripts that had premature stop codons in the sensitive but not the resistant biotype. These transcripts and their products should be the subject of future studies to determine if and how they are involved in resistance.

Salmonella spp. is a human pathogen that has been reported in catfish, but with conflicting results. Salmonella spp. was isolated from live catfish, catfish products and the processing environment during catfish production, followed by evaluation of their antibiotic resistance and clonal similarities. Distinction of Salmonella spp. was increased by lowering background microflora with the addition of the antimicrobial novobiocin to the agar media. More than ten Salmonella serotypes were isolated from catfish and catfish products, such as live, chilled fillets, frozen fillets, and conveyor belts in catfish processing facilities. The isolates that were recovered include Salmonella ser. Typhimurium, Barranquilla, Mbadaka, Putten, Infantis and Thompson among others. The number of isolated Salmonella spp. and serotypes varied between sampling in catfish facilities. Clonal similarities of Salmonella spp. were found within sampling but did not show persistency among sampling periods, suggesting the opportunistic nature of the pathogen. Salmonella ser. Typhimurium was the most predominant isolate in live catfish and similarities were found within sampling but were not persistent among sampling periods. Antimicrobial resistant Salmonella was identified from the recuperated isolates. All Salmonella spp. isolates, showed resistance to erythromycin, vancomycin and rifampin regardless of the serotype, but resistant genes were absent suggesting that resistance was due to the pathogen’s biological nature. These results suggest that it is possible to recover Salmonella spp. in catfish products, but its opportunistic nature makes it difficult to predict the source or incidence of this pathogen.

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