ABSTRACT Early‐stage herbicide discovery often relies on glasshouse assays that can take extended time periods before effects are detected, a limitation that is especially problematic for woody weeds. These pipelines also demand large quantities of candidate compounds at field‐equivalent rates, which are rarely available during early discovery. In contrast, standard multiwell plate assays offer rapid, low‐volume alternatives but are restricted to small‐seedling model species, limiting their relevance for large‐seedling weeds. Here, an in vitro whole‐plant assay for post‐emergence herbicide screening was developed to detect intrinsic herbicidal activity in the large‐seedling weed Cryptostegia grandiflora (rubber vine), a major invasive woody vine in tropical and subtropical regions, and benchmarked against a controlled glasshouse assay. Herbicides were applied at a single conservative dose (0.1 mM; 100 μL per seedling), and six commercial herbicides with known activity against rubber vine were assessed across three modes of action: acetolactate synthase (ALS) inhibitors (metsulfuron‐methyl, imazapyr), auxin mimics (2,4‐D, triclopyr) and photosystem II (PSII) inhibitors (hexazinone, tebuthiuron—primarily soil‐applied, included for comparison). Both systems detected strong herbicidal activity, but response timing and endpoints differed. ALS inhibitors consistently suppressed height, with delayed mortality in the glasshouse and no mortality in vitro, confirming height reduction as an early indicator of ALS activity. Auxin mimics induced rapid, near‐complete mortality in both systems, with earlier responses in vitro. Hexazinone was effective across assays, whereas tebuthiuron showed weak activity in the glasshouse but strong activity in vitro. The in vitro assay substantially reduced screening timelines compared with conventional approaches, producing treatable seedlings within 16 days and detecting activity within 1–3 weeks depending on mode of action. This approach complements glasshouse trials as an early‐stage prioritisation tool for weed‐specific screening of scarce compounds, and may support rapid resistance monitoring and herbicide discovery in other large‐seedling invasive weeds following further validation.
Batista et al. (Sun,) studied this question.