The mechanism of diflufenican resistance and its inheritance in oriental mustard (Sisymbrium orientale L.) from Australia

Discovery of N-benzyl-6-methylpicolinamide as a potential scaffold for bleaching herbicides

BACKGROUND

In pesticide research, bleaching herbicides have always been a hot topic. Our previous research showed that N-(4-fluorobenzyl)-2-methoxybenzamide is an innovative lead compound for bleaching herbicides.

RESULTS

A total of 40 derivatives of picolinamides were prepared and evaluated for their herbicidal activity by Petri dish tests and postemergence trials. The structure-activity relationship (SAR) revealed that introducing electron-withdrawing groups at the 3- or 4-positions of the benzyl significantly enhances herbicidal activity. Furthermore, ZI-04 induced similar symptoms such as bleaching effect in treated weeds and accumulation of biosynthetic precursors for carotenoids as observed with diflufenican. ZI-04 also exhibited significant cross-resistance to diflufenican and had a lower resistance risk than diflufenican.

CONCLUSION

N-benzyl-6-methylpicolinamides were discovered as a novel scaffold for bleaching herbicides. The accumulation of phytoene, phytofluene and ζ-Carotene in radish cotyledons, and cross-resistance observed with diflufenican, showed that title compounds can interfere with carotenoid biosynthesis. © 2024 Society of Chemical Industry.

The Genetic Components of a Natural Color Palette: A Comprehensive List of Carotenoid Pathway Mutations in Plants

Carotenoids comprise the most widely distributed natural pigments. In plants, they play indispensable roles in photosynthesis, furnish colors to flowers and fruit and serve as precursor molecules for the synthesis of apocarotenoids, including aroma and scent, phytohormones and other signaling molecules. Dietary carotenoids are vital to human health as a source of provitamin A and antioxidants. Hence, the enormous interest in carotenoids of crop plants. Over the past three decades, the carotenoid biosynthesis pathway has been mainly deciphered due to the characterization of natural and induced mutations that impair this process. Over the year, numerous mutations have been studied in dozens of plant species. Their phenotypes have significantly expanded our understanding of the biochemical and molecular processes underlying carotenoid accumulation in crops. Several of them were employed in the breeding of crops with higher nutritional value. This compendium of all known random and targeted mutants available in the carotenoid metabolic pathway in plants provides a valuable resource for future research on carotenoid biosynthesis in plant species.

Non-target-site resistance to PDS-inhibiting herbicides in a wild radish (Raphanus raphanistrum) population

BACKGROUND

Diflufenican resistance has been reported in wild radish populations since 1998, but the resistance mechanisms have not been investigated. Recently, we identified a wild radish population (H2/10) from the Western Australian grain belt that is resistant (R) to the phytoene desaturase (PDS)-inhibiting herbicide diflufenican.

RESULTS

Dose-response results showed this R population is 4.9-fold more resistant than the susceptible (S) population based on the LD₅₀ R/S ratio. In addition, the R population also exhibits cross-resistance to the PDS-inhibiting herbicide fluridone. The cytochrome P450 inhibitor malathion reversed diflufenican resistance and partially reversed fluridone resistance in the R population. The full coding sequences of the PDS gene were cloned from the S and R plants and there are natural variations in the PDS gene transcripts/alleles with no correlation to resistance. In addition, the R plants had a level of PDS gene expression that is not significantly different from the S plants.

CONCLUSION

These results demonstrated that diflufenican resistance in this R wild radish population is likely due to non-target-site based enhanced herbicide metabolism involving cytochrome P450s. © 2019 Society of Chemical Industry.

Target-Site Mutations Conferring Herbicide Resistance

Mutations conferring evolved herbicide resistance in weeds are known in nine different herbicide sites of action. This review summarizes recently reported resistance-conferring mutations for each of these nine target sites. One emerging trend is an increase in reports of multiple mutations, including multiple amino acid changes at the glyphosate target site, as well as mutations involving two nucleotide changes at a single amino acid codon. Standard reference sequences are suggested for target sites for which standards do not already exist. We also discuss experimental approaches for investigating cross-resistance patterns and for investigating fitness costs of specific target-site mutations.

No apparent fitness costs associated with phytoene desaturase mutations conferred resistance to diflufenican and picolinafen in oriental mustard (Sisymbrium orientale L.)

Two mutations Leu498 and Glu425 in the PDS gene were identified as the main cause conferring resistance to diflufenican and picolinafen in two oriental mustard populations P3 and P40. As mutations are suspected to affect fitness, this study was designed to test this hypothesis using the F₂ of two crosses P3.2 (P3♂ × S♀) and P40.5 (P40♂ × S♀) of oriental mustard. The F₂ plants, which segregated for target-site point mutations of PDS gene (Leu498 and Glu425) grown in monoculture and under competition with wheat in pot-trials and evaluated for growth and fecundity. All F₂ individuals were genotyped by using Cleaved Amplified Polymorphic Sequence (CAPS) technique. Regression analysis showed no fitness cost in the resistant plants because no significant difference was identified in seed and biomass production within RR, RS and SS individuals. The absence of measurable negative effects on fitness associated mutations suggests that the frequency of the PDS resistance alleles will not decline in the absence of selection pressure of PDS-inhibitors.

Cross-resistance to diflufenican and picolinafen and its inheritance in oriental mustard (Sisymbrium orientale L.)

BACKGROUND

An oriental mustard population (P40) was identified as resistant to diflufenican by screening at the field rate. As diflufenican and picolinafen both target phytoene desaturase (PDS), cross-resistance to picolinafen was suspected. The mechanism of resistance and its inheritance to diflufenican and picolinafen were investigated.

RESULTS

At the lethal dose (LD₅₀ ) level, population P40 was 237-fold more resistant to diflufenican and seven-fold more resistant to picolinafen compared to two susceptible populations. Population P40 also had a significantly higher resistance to diflufenican (237-fold) than a previously described P3 population (143-fold). In addition to the Leu-498-Val mutation in PDS identified in all individuals of the P3 and P40 populations, a Glu-425-Asp mutation was also found in P40. Neither mutation was detected in any individuals of the susceptible population. As the segregation of phenotype and genotype of the F₂ individuals fitted the model for a single dominant allele, resistance to both diflufenican and picolinafen is likely encoded on the nuclear genome and is dominant.

CONCLUSION

Resistance to diflufenican and picolinafen in the P40 population is likely conferred by Leu-498-Val and Glu-425-Asp mutations in the PDS gene. Inheritance of resistance to these herbicides is managed by a single dominant gene. © 2018 Society of Chemical Industry.