An evaluation of tenuazonic acid, a potential biobased herbicide in cotton.

Tenuazonic acid (TeA), a putative nonhost-selective mycotoxin isolated from Alternaria alternata, is the main causative agent of brown leaf spot disease of crofton weed (Ageratina adenophora) and some other crops. Previous studies revealed that it is a natural photosystem II inhibitor that binds the D1 protein to block electron transfer. Though the crude metabolite extract of A. alternata containing TeA has been bioassayed, the herbicidal activity of synthesized TeA has not been systematically evaluated yet.

TeA caused leaves of crofton weed to have brown spots that were more pronounced in older leaves than younger ones. It completely killed 92% of the four-leaf seedlings at 600 g ai/ha but only 81% or less of six-leaf seedlings or bigger. The bioassay of phytotoxicity of TeA to 67 plant species including 54 weeds and 13 crops, showed that TeA had a broad weed spectrum but low toxicity to Solanaceae and Malvaceae species. Further potted- plant experiments demonstrated that TeA had EC₉₀ values that ranged from 119 to 795 μg/mL for 14 important weeds but was 2539 μg/mL for Acalypha australis. Nicotiana tabacum and Gossypium hirsutum had no injury symptoms at 1000 μg/mL. A field trial showed that TeA effectively controlled two important weeds, Digitaria sanguinalis and Amaranthus retroflexus without affecting cotton in the field.

TeA has potential as a biobased herbicide for controlling important dicotyledon and monocotyledon weeds in cotton and tobacco fields. © 2019 Society of Chemical Industry.