Characterizing 2,4‐D Rapid Response Resistance in Conyza sumatrensis

ABSTRACT

Resistance to 2,4‐D has evolved in Conyza sumatrensis , with some resistant accessions expressing rapid response (RR) resistance, characterised by rapid necrosis followed by regrowth. This study evaluated biochemical and physiological changes in two RR‐resistant accessions after treatment with 2,4‐D and other auxinic herbicides. RR symptoms occurred only with 2,4‐D, while clopyralid, triclopyr, florpyrauxifen‐benzyl and dicamba caused complete mortality. In RR‐resistant accessions, exposure to 2,4‐D resulted in a threefold increase in superoxide dismutase activity, a 45% decline in PSII efficiency, reductions of up to 95% in photosynthesis and 40%–60% reductions in transpiration compared to susceptible plants. Necrosis was enhanced by light and the availability of cytokinin and sucrose, resulting in a reduction in green leaf area. Foliar uptake of 2,4‐D was approximately 11% greater in RR‐resistant accessions compared to the susceptible one, but translocation was approximately half of that in the susceptible accessions. These results indicate that RR resistance in C. sumatrensis involves reduced translocation, enhanced antioxidant capacity and an energy‐linked process triggered specifically by 2,4‐D. From a practical perspective, our findings confirm that RR‐resistant accessions do not have cross‐resistance to other auxinic herbicides, supporting chemical rotation options and reinforcing the need for integrated management strategies to limit the spread of this resistance phenotype.