Herbicide Potential of Selected Essential Oils From Plants of Lamiaceae and Asteraceae Families

Essential oils from Monarda fistulosa L., Satureja pilosa Vel., Origanum vulgare subsp. hirtum Ietswaart. (Greek oregano), Micromeria dalmatica Benth., Thymus longedentatus (Degen & Urum.) Ronniger, and Artemisa campestris L. were evaluated as inhibitors of seed germination in target plants Lolium perenne L. and Trifolium pratense L. using in vitro assays. The essential oils were applied on the seeds as aqueous solutions at concentrations ranging from 0.5–3.0 µL/mL. Complete inhibition was established at a concentration of 1.5 µL/mL with the most effective essential oils. Oregano oil was evaluated for its inhibitory activity on seed germination under field conditions; the essential oil was applied as an aqueous solution at concentrations of 3, 5, and 10 µL/mL on superabsorbent Terawet. The mass obtained was mixed with the seeds of the target plants and planted in a field. After 1 month, the results were evaluated based on the weight of the aerial parts of the plants from control and experimental areas. At the highest concentration studied, the weight of the plants was 77% lower in the experimental areas than in the controls. The chemical composition of the essential oils was analyzed using gas chromatography–mass spectrometry. The results showed that carvacrol-rich essential oils had a strong inhibitory effect on seed germination. The inclusion of the essential oil on a superabsorbent was a good way to preserve its herbicidal activity under field conditions as this prevented its rapid evaporation.

Fruit juice mediated multicomponent reaction for the synthesis of substituted isoxazoles and their in vitro bio-evaluation

A simple, efficient and eco-friendly procedure for the synthesis of isoxazole derivatives (4a–4h) using one-pot three-component reaction between substituted aldehydes (1a), methyl acetoacetate (2a) and hydroxylamine hydrochloride (3a) has been achieved in presence of Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice respectively. The homogeneity of synthesized compounds was confirmed by melting point and thin layer chromatography. The synthesized compounds were characterized by using 1H NMR, FTIR and CHN analyses and evaluated for in vitro herbicidal activity against Raphanus sativus L. (Radish seeds). The compounds (4a–4h) were also screened for their fungicidal activity against Rhizoctonia solani and Colletotrichum gloeosporioides. Antibacterial activity was also tested against Erwinia carotovora and Xanthomonas citri. From bio-evaluation data, it was found that compound 4b was most active against Raphanus sativus L. (root) and Raphanus sativus L. (shoot) respectively. Compound 4b was also found most active against both the fungus viz. R. solani and C. gloeosporioides showing maximum percentage growth inhibition i.e. 90.00 against R. solani and 82.45 against C. gloeosporioides at 2000 µg/mL concentration. Compound 4 h has shown maximum inhibition zone i.e. 3.00–9.60 mm against Erwinia carotovora at 2000 µg/mL concentration. Maximum Xanthomonas citri growth was also inhibited by compound 4 h showing inhibition zone 1.00–5.00 mm at highest concentration.

In Silico Structure-Guided Optimization and Molecular Simulation Studies of 3-Phenoxy-4-(3-trifluoromethylphenyl)pyridazines as Potent Phytoene Desaturase Inhibitors

A series of novel 3-phenoxy-4-(3-trifluoromethylphenyl)pyridazines 2–5 were designed, based on the structure of our previous lead compound 1 through the in silico structure-guided optimization approach. The results showed that some of these new compounds showed a good herbicidal activity at the rate of 750 g ai/ha by both pre- and post-emergence applications, especially compound 2a, which displayed a comparable pre-emergence herbicidal activity to diflufenican at 300–750 g ai/ha, and a higher post-emergence herbicidal activity than diflufenican at the rates of 300–750 g ai/ha. Additionally, 2a was safe to wheat by both pre- and post-emergence applications at 300 g ai/ha, showing the compound’s potential for weed control in wheat fields. Our molecular simulation studies revealed the important factors involved in the interaction between 2a and Synechococcus PDS. This work provided a lead compound for weed control in wheat fields.

Herbicidal Effects of Ethyl Acetate Extracts of Billygoat Weed (Ageratum conyzoides L.) on Spiny Amaranth (Amaranthus spinosus L.) Growth

This study aimed to evaluate the herbicidal activity of ethyl acetate leaf extract of Ageratum conyzoides L. at different subfractions on Amaranthus spinosus L. The leaves of A. conyzoides were sequentially extracted with n-hexane and ethyl acetate respectively and fractionated by chromatography column. The extracts were applied to A. spinosus in pot assays at a concentration of 5%, 10% and 15%. We applied A synthetic herbicide (2,4-D at 0.686 kg a.i. ha−1) for positive control and distilled water for negative control. The A. conyzoides extracts strongly differed in their effect on weed control, shoot and root dry weight and root length of A. spinosus. The most inhibition on A. spinosus growth caused by application of ethyl acetate of A. conyzoides extracts subfraction A by 10% concentration can cause 100% destruction and subfraction B were 95% which both of them cause strongest death on A. spinosus compared with synthetic herbicide (2, 4-D) (23.33%) at 1 Day After Application, while subfraction C and D were not effective. Main constituents identified by GC-MS in subfraction A extract were tetradecanoic acid, ethyl ester (10.26%), precocene II (9.39%), octadecanal (8.23%), 9,12,15-octatadecatrienoic, methyl ester (7.32%), 10-heneicosene (c,t) (5.19%) and neophytadiene (5.09%); in subfraction B were 1-octadecyne (38.57%), phytol (11.24%), di-tert-utylphosphine-d (5.17%) and 1-hexadecine (4.08%); in subfraction C were allobarbital (8.53%), octadecanal (12.69%), and bannamurpanin (26.01%) and octadecanal (30.52%), bannamurpanin (24.06%), 1,8-cineole (15.75%), trans-dodec-5enal (12.28%) and phytol (8.26%) in subfraction D. The ethyl acetate extract subfraction A and B concentration 10% proved the promising control agent against A. spinosus.

Inhibition of chloroplast translation as a new target for herbicides

The rise in herbicide resistance over recent decades threatens global agriculture and food security and so discovery of new modes of action is increasingly important. Here we reveal linezolid, an oxazolidinone antibiotic that inhibits microbial translation, is also herbicidal. To validate the herbicidal mode of action of linezolid we confirmed its micromolar inhibition is specific to chloroplast translation and did not affect photosynthesis directly. To assess the herbicide potential of linezolid, testing against a range of weed and crop species found it effective pre- and post-emergence. Using structure-activity analysis we identified the critical elements for herbicidal activity, but importantly also show, using antimicrobial susceptibility assays, that separation of antibacterial and herbicidal activities was possible. Overall these results validate chloroplast translation as a viable herbicidal target.